Maryam Bachelor thesis

Synthesis and characterization
of BaMxTi(1-x)O(3-δ)
(M=In, Fe, Sc)
Maryam Ayeb
Degree project for Bachelor of Science in
Chemistry
30 hec
Department of Chemistry
and Molecular Biology
Universityof Gothenburg

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Supervisor: Seikh M.H Rahman Department of Chemistry and Chemical Engineering.
Co-supervisor: Zareen Abbas, Department of chemistry and molecular-biology.
Examiner: Jan Pettersson, Department of chemistry and molecular-biology.
Bachelor Thesis 2017:24
Department of Chemistry and Chemical Engineering
Material Chemistry
Oxide group
Chalmers University of Technology
SE-412 96 Gothenburg
Telephone +46 31 772 1000
Department of Chemistry and Molecular Biology
University of Gothenburg
SE-412 96 Gothenburg
Telephone +46 31 786 0000
Bachelor project for studying the behaviour of doped BaTiO3 with different doping elements like
scandium, iron and indium.
© AYEB, 2017.
Keywords: BaTiO3, hexagonal and cubic perovskite, proton conductivity, SEM, TGA, IR, XRD, Rietveld
refinement, solid-state reaction, wet chemical route, sol-gel method.

Abstract:
Doping is a chemicalmodificationtoimprove theconductivity aswell creating oxygen vacanciesin asolid
structure. The aim of this thesis is to investigate structural characteristics, oxygen vacancies and
electrical conductivity of BaTiO3 doped with indium, iron and scandium.
BaMxTi(1-x)O(3-δ) (x=0,17 and 0,33) were prepared via solid state reaction as well through wet chemical
route. Thematerials have been characterizedwith X-ray diffraction(XRD),scanningelectron microscopy
(SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and
impedance spectroscopy to determine the crystallinity of pure phases, microstructure, oxygen vacancies
and conductivity. From the Rietveld refinement of diffraction pattern, it was found that the iron doped
samples have a hexagonal perovskite structure while indium doped materials have a cubic perovskite
structure.
The indium doped materials required higher temperature and longer sintering time compared to the
iron doped materials to obtained pure phases. The thermogravimetric analysis revealed that all as-
prepared samples had significant hydration levelbetween68-93% of the maximum theoretical hydration
level. Increasing the ratio of doping in iron doped material resulted in denser microstructure, while for
indium doped material the density decreased. However, the highest density was achieved through wet-
chemical route compared to solid state route. The wet chemical route also slightly increased the density
of iron doped material (86,5%) compared to the solid-state route.
Thermogravimetric analysis for both as-prepared and hydrated samples has shown mass loss, which is
the main indication of up taking of water in humid environment. The FT-IR confirmed the presence of
broad 𝑂 − 𝐻 stretching band in all hydrated samples compared to the vacuum dried ones. The
measurements with AC impedance spectroscopy have shown a slightly higher total conductivity under
humid atmosphere compared to the dry atmosphere and materials show p-type electronic conduction.

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Table of Contents:
TABLE OF CONTENTS: 1
LIST OF ABBREVIATIONS 4
1 INTRODUCTION 5
1.1 BACKGROUND 6
1.1.1 Aim of the project: 6
2 THEORY 7
2.1 PROTONCONDUCTIONSOLID OXIDE FUEL CELLS (PC-SOFC) 7
2.2 THE PEROVSKITE STRUCTURES 7
2.3 THE STRUCTURE OF BARIUM TITANIUM OXIDE 8
2.4 SOLID STATE REACTION (CERAMIC METHOD) 9
2.5 WET-CHEMICAL ROUTE (SOL-GEL METHOD) 10
2.5.1 Hydrolysis of inorganic precursors 10
2.5.2 Condensation mechanism in inorganic precursors 11
2.6 DEFECT AND PROTONTRANSFERS 12
2.6.1 Proton transport and the mechanism in ceramic materials 12
2.7 ANALYTICAL TECHNIQUES 14
2.7.1 X-ray powder diffraction technique (PXRD) 14
2.7.2 Rietveld refinement 15
2.7.3 Fourier transform infrared spectroscopy (FT-IR) 16
2.7.4 Electrochemical Impedance spectrosopy (EIS) 18
2.7.5 Scanning electron microscopy (SEM) 19
2.7.6 Thermogravimetric Analysis (TGA) 20
3 METHODS 21
3.1 SAMPLE PREPARATION 21
3.1.1 Solid state reaction 21
3.1.2 Wet chemical route (sol-gel method) 22
3.1.3 Vacuum drying and protonation of the samples 23
3.1.3.1 Vacuum drying the sample 23
3.1.3.2 Protonation of the sample, Hydration method 23
3.2 CHARACTERIZATIONMETHODS 24
3.2.1 X-Ray powder diffraction (PXRD) 24
3.2.3 Electrochemical impedance spectroscopy (EIS) 24
3.2.4 Thermogravimetric analysis (TGA) 25
3.2.5 Fourier transform infrared spectroscopy (FT-IR): 25
4 RESULTS 26
4.1 IRONDOPED BATIO3 26
4.1.1 X-ray powder diffraction (XRPD) 26
4.1.5 Scanning electron miscroscopy (SEM) 31
4.2 INDIUM DOPED BATIO3 33
4.2.1 X-ray powder diffraction (PXPD) 33
5 DISCUSSION 39

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5.1 STRUCTURE 39
5.1.1 Hexagonal 39
5.1.2 Cubic 40
5.2 TGA & FT-IR 40
5.3 CONDUCTIVITY 41
6 CONCLUSIONS 42
7 FUTURE WORK: 43
8 APPENDIX A: FIGURES 44
8.1 X-RAY DIFFRACTION 44
9 APPENDIX B: CALCULATIONS: 47
9.1 RELATIVE DENSITY 47
9.2 THE HYDRATIONPERCENTAGE 48
9.3 THE TOTAL CONDUCTIVITY AND ACTIVATIONENERGY CALCULATION (IMPEDANCE DATA) 49
10 ACKNOWLEDGMENT: 49
11 BIBLIOGRAPHY 50

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“Blessed are those who are not afraid to admit that they don’t know something.”
𝑇ℎ𝑒 𝑍𝑎ℎ𝑖𝑟 (2005), 𝐴𝑢𝑡ℎ𝑜𝑟 𝑃𝑎𝑢𝑙𝑜 𝐶𝑜𝑒𝑙ℎ𝑜 𝐴𝑢𝑡ℎ𝑜𝑟 (𝐴𝑢𝑔𝑢𝑠𝑡 24,1947)

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List of Abbreviations
AC Alternating Current
BTF Barium Titanium Iron oxide
BTI Barium Titanium Indium oxide
BTS Barium Titanium Scandium oxide
C Capacitor
χ chi
i current
σ Conductivity (Scm-1/(Ωcm)-1
DC Direct current
DCS Differential Scanning Calorimetry
Ea Activation energy
eV Electron volt
FT-IR Fourier Transform Infrared spectroscopy
IS Impedance spectroscopy
θ Incidence angle of X-ray beam
dhkl Lattice d-spacing
PXRD Powder X-Ray Diffraction
R Resistance
Rwp Weight profile index
Rexp Expected index
SEM Scanning Electron Microscopy
SOFC Solid Oxide Fuel Cell
SSR Solid State Reaction
S.R Sintering reaction
TGA ThermoGravimetric Analysis
v Voltage
WCR Wet-Chemical Route
λ X-ray beam wave-length

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1 Introduction
Nowadays, human’s activities are the leading cause of the global warming resulting from high
pollution level. The most consumed energy resource is fossil fuels, which emit greenhouse gases
that contribute to the global warming. However, newest technologies are more and more based
on renewable energy, which in turn will minimize the pollution.
Fuel oxide cell is the new generation’s power
source that could evolve and work in different
applications as well can minimize the pollution
level. The central role of the fuel cell is to convert
the chemicalenergy from the hydrogen-based fuel
to an electrochemicalenergy. Instead of producing
carbon dioxide, the fuel cell produces water and
limits the atmospheric pollution.
There are different types of fuel cells as alkaline
membranes (AFC), proton exchange membrane
(PEMFC), direct methanol (DMFC), phosphoric
acid (PAFC), molten carbonate (MCFC) and solid
oxide (SOFC). The most suitable one for ceramic
materials is SOFC(solid oxide fuelcell).The mobile
ions in SOFC are O2- and H+ and have an operating
temperature around 600°C-900°C. The high
operating temperature is themain factorleadingto
a slow start-up depending on the slow oxygen ion
transport through the electrolyte at low
temperature.[14, 15]
One of the benefits of using SOFC compare to other cells is that it is suitable for all sizes of
combined heat and power systems. Proton conducting fuel cell (PCFC) is a sub-class of the SOFC
and has the intermediate operating temperature between 200-600°C, lower than the classical
SOFC. The advantages of proton conducting electrolyte over the standard oxygen ion conducting
electrolyte is the stability as well the high ion conductivity at low temperatures. This type of fuel
cell could be used in different applications like; steam electrolysers, humidity and hydrogen
sensors. [9, 16-18] The SOFC system is the most powerfulsystem that is capable of generating power
around 10kW to 10MW. [14, 19]
As shown in Fig.1 oxygen ions move from the cathode through the electrolyte to the anode and
combine with hydrogen at the other part. The products of this reaction are water and two free
electrons from the anode. These reactions produce power when the electron discharges at the
electrolytesite. Theideal electrolyteshould full-fillcertainproperties: high ionic conductivity,high
strength, durability: long-lived, low temperature performance and stability.
Perovskites have recently been in focus due to their structure and useful properties which can be
achieved by cations variation and substitutions (doping effect). The doping effect creates oxygen
vacancies and the primary source for it is the charge replacement of the acceptor-typecations and
an effect of structural defect. The oxygen vacancies created in structure could be hydrated using
heat treatment and humid atmosphere (hydration experiment). Under humid atmosphere the OH-
group is filling the oxygen vacancies while the H+ is binding to the lattice oxygen. The proton
Figure 1:PCFC and SOFC that are combined to create the ideal
cell.

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conductivity is a result of a chemical mechanism; the hydrogen jumping by Grotthus mechanism
(as described in section defect and proton transfers theory) around different oxygen molecules.[20]
1.1 Background
Developing fuel cell technology based on solid oxides have many advantages over other energy sources
such as a high energy efficiency,low pollution level and flexibility in possibility of improving the design
of energy cell. Proton conducting oxide fuel cell is a subclass of SOFC, where the operating temperature
is between 200-600°C. Different perovskite structures with dopants such as iron, indium and scandium
have been studied forseveral years. However,many different structures have been reported depending
on different doping ratios as well as differences in the analysis methods. The proton conducting
electrolytes are lower-valence substituted perovskites and these materials have been extensively
studied.[16-18, 21-24]
Y-doped BaZrO3 or BaCeO3 are known as good proton conducting ceramic materials with an optimal
operating temperature 300-600°C. Cerates (for example BaCeO3) are unstable in the atmosphere and
could decompose into BaCO3 in the presences of CO2. Yttrium doped BaZrO3 perovskite has shown both
stability and high bulk proton conductivity. The higher substitution that refills with a doped material
(Sc, In, Yb or Y) leads to a higher proton conductivity compared to the lower doping ratio. Zirconates
are more stable and also showing lower grain-boundary conductivity than cerates. Some previous
studies about BaZrO3 system doped with In, Yb, and Sc have shown an increasing amount of oxygen
vacancies due to the increase of the doping level, whichleads to a higher proton conductivity.[16, 21, 22, 24-
26]
Few studies have focused on proton conductivity for doped BaTiO3. Iron
doped BaTiO3 classified as a multiferric material due tothe high dielectric
constant but also for a large ferroelectric transition temperature. The
substitution of titanium ion by iron ion introduces the ferromagnetic
ordering in BaTiO3, and the replacement leads to transformation of the
material into a semiconductor (from n-type to p-type). The iron doped
materials adapt a hexagonal structure and the structure changes from
tetragonal structure to hexagonal, when the doping ratio increases. The
ferromagnetic properties depend on the substitution level of the
material.[27-29]
As shown in Torino's article[24], the scandium doped BaTiO3 has higher
protonconductivity athigher substitution ratio. Researchers have studied
different conducting materials at different temperature as illustrated in
Fig.2. There is a “gap” produced at 200-600°C, which is called proton
conducting gap. Many applications require quite low operating
temperature.
1.1.1 Aim of the project:
The main motivation of this project is to produce materials with similar properties as and study both
structural as wellelectricalproperties forall samples. This projectis designed to study the lower-valence
substituted BaTiO3 perovskites (BaMxTi(1-x)O(3- δ)) where the substituents are Sc, In and Fe and x=0,33
and x=0,17. A comparison between synthesis routes is important to understand if it is the main reason
promoting the conductivity as well the structure. The project will also include a description of detailed
Figure 2:Different conducting materials
where proton conducting gap is
between 200-600C°[9]

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structural analysis and how the structure is related toconductivity[16, 24, 26].Thesynthesised materials will
be oxides that have the same properties as electrolyte and cathode material. These materials are
important component for renewable energy source in SOFC system. [9, 30]
2 Theory
2.1 Proton Conduction solid oxide fuel cells (PC-
SOFC)
Protonconducting oxide fuel cells consist of two different parts, an anode and a cathode connected by an
electron conductingwire, as well solid oxide electrolyte in-between the anode and cathode, to enable the
proton transport through the electrolyte as shown in Fig.1. The anode should not be oxidized under the
operating temperature. The anode must facilitate the reaction between the hydrogen based fuel and the
electrolyte in order to produce sufficient number of protons. It is also important for the anode to be
porous to establish wide contactwiththe fuel,same properties are important forthe cathode part as well
in order to facilitatethe reaction between H+ and O2-[14, 19]. The reactions occurringon anode and cathode
for solid oxide fuel cell are given below:
2.2 The perovskite structures
The general formula forperovskite is ABX3 where bothA and B are
cations while X is the anion. The A cation and the X anion have the
same size whilethe B cationis smaller in size. TheA-site isdivalent
cation and the B-site is tetra cation where the B cation is in the
centre of the octahedron surrounded by 6 X atom, usually oxygen.
Meanwhile, the A cation is located at the centre of twelveX anions.
The classical chemical way to describe the position in perovskite
structure where the A site is located at the centre of the cell and X
anion set at the middle of the edge, this is called B cell setting.
The perovskite structure depends on the size of both A and B ions.
If the ionic radii difference is large this will result in increased
distortion in the structure. The Goldschmidt Tolerance factor (𝑡)
as shown in eq.2 is a factor which is calculated to determine the
perovskite structure.
𝐴𝑛𝑜𝑑𝑒 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛: 2𝐻2 4𝐻+ + 4𝑒− (1)
𝐶𝑎𝑡ℎ𝑜𝑑𝑒 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛: 𝑂2 + 4𝑒−  2𝑂2−
4𝐻+ + 2𝑂2−  2𝐻2 𝑂
Figure 3:General structure of
perovsite, where Ba ion (green), Ti ion
(black) which is surrounded by
octahedral oxygen (purpule).[13]

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𝑡 =
𝑟 𝐴+𝑟 𝑂
√2( 𝑟 𝐵+𝑟 𝑂) (2)
For the cubic structure the tolerance factor will be between 0,8 - 1,10, while for hexagonal or
tetragonal structure the t-factor is >1. Other aspects could also affect the structure like metal-
metal interaction and the degree of the covalence.
The A-cell setting, placing the B-site at the centre of the cell and the X are face centred (at the
centre of the cube faces). By doping the perovskite, the B-cations are substituted by a different
and lowervalent cation to create oxygen vacancies. The oxygen vacanciescould contribute along
with other proprieties such as proton conductivity. [27, 28, 31]
According to “hydrogenin oxide” that is written by Truls Norby[32], the electronegativity fromthe
B site which is titanium in BaTiO3 could affectthe hydration and the ability of trapping protons.
Norby have additionally realized the connection between electron-negativity and enthalpy. For
example, if the differencebetween A and B site electron-negativity is smaller, then it contributes
to a larger negative hydration enthalpy (i.e. the more readily the material hydrates).
2.3 The structure of barium titanium oxide
The well-knownBaTiO3 dielectric capacitorsare heavily studied as wellused, whereferroelectric
and dielectric properties are the most common properties of BaTiO3. This material had been
discovered during the World War II (1941). Another specific known property for BaTiO3 is the
para-electric material at high temperatures[33].
The first studies were done on doping TiO2 with BaO, which produced BaTiO3 ceramic material.
The oxide had been synthesized by Thurnaurer & Deaderick in early 1941 at the American Lava
Corporation. In 1945-1946 Von Hippel, Wul and Goldman validated the ferroelectric in simple
ceramic materials and have shown that they fitted in the perovskite group[33]. As illustrated in
Fig. 3, BaTiO3 has a cubic structure where the barium atom is in the centre of the cell and the
titanium atoms are surrounded by octahedral oxygen (coordinated to 6 oxygen ions) and the
barium ion is coordinated with 12 oxygen ions.[27, 28, 34]
By doping the material, the cations are substituted with a lower valence cation, which induces a
charge imbalance in the structure. The balance is restored by elimination of oxygen anions and
creating oxygen vacancies. The substituted perovskites are used in solid state proton conductors
typically to exhibit the highest proton conductivity in the cubic form. Their general formula can
be written as AB(1-x)MxO(3-δ), where δ =x/2. Divalent alkaline earth metals are occupying the A-
site and trivalent metals are occupyingthe B-site along withthe rare-earth dopant metals (M) of
lower valence. The δ is the total oxygen deficiencies as in the example of the perovskite
BaZr(1-x)YxO(3-δ).
If barium titanate is partly substituted with a comparable electronegative atom to barium or
lower than titanium, the substitution will result in higher hydration level, and greater
temperature stabilized protonic defects. It should be noted, that concerns have been raised
regarding the validity of this correlationforhigh substitution levels, something whichwill also be
considered in the discussion section. 12,15,[35]

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2.4 Solid state reaction (ceramic method)
The most used technique to produce a high-temperature oxide is solid-state reaction, also called
the ceramic method. This method consists of simple steps as stoichiometric weighing the starting
materials (metal oxides, metal carbonates or salts) and grinding the mixture in agate mortar and
pestle orball-milling toreduce the particle size and even increase the homogeneity of the sample.
In order to accomplish the reaction and the inter-diffusion of the cations, the sample is pressed
into pellet(s) and heated with increased temperature programme. Different factors could affect
the solid-state reaction as the particle size of the mixture, the mixing process, and the slow
reaction (the pure phase could be achieved in days and weeks).
The sample is layered structure where different types of oxide layers make a connection with
each other. For example, AO and BO2 and the product ABO3 phase will be produced continuously
through inter-diffusion route.
The inter-diffusion mechanism is a process of diffusing ions to achieve a homogeneous mixture.
Solid state reaction is a slow process as the ions are diffusing a long distance through the desired
product. Unwanted phases are always easy to be produced and they may be formed in the
reaction. It is important for the sample to be grinded after each treatment and heating is needed
for the diffusion mechanism to accomplish the reaction. The final product ABO3 has a large
concentration of defects, which facilitates the diffusion mechanism.
To simplify the diffusion of the ions, the powder is pressed into pellet(s) after the grinding
process. The high temperature is promoting the reaction and the inter-diffusion of ions.
Increasing the surface area for reactants help the reaction to be completed. Under the diffusion
condition, the phase boundary is grouped at the interface of the bulk for each particle between A
and AB as well as between B and AB.
Solid state reaction depends on the diffusion-rateof the species, wherethe rate could be the same
or different from each other. The reason why the reaction cannot be accomplished at AB phase
depends upon the different structure of the AB phase compared to the structure of A and B.
Except for the long period of grinding and high temperature heating the sample, there are other
disadvantages in solid state reaction as; stoichiometry loss for reactant due to the high
temperature during the reaction,different particle sizes and shape makes it difficulttoreproduce
the same material with the same temperature program. Kinetic and thermodynamic factors are
Figure 4: The traditional solid state reaction or as known ceramic
method.[5]

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also important in the ceramic method, the reaction between twosolids (heterogeneous) and the
formation of the product, which occurs at the interface. [27, 28, 31]
2.5 Wet-chemical route (sol-gel method)
The wet chemical route or sol-gel method is a technique whichis based on dissolving and mixing
the precursors into a solution or a sol-gel suspension at certain pH to prevent precipitation. After
the solution has transformed into a gel, the gel is dried and preheated up to 300°C to evaporate
all organic compounds. The advantage of this technique is that with single calcinationstep a pure
product can be synthesized, if all precursors have reacted in solution. Different additives such as
chelating agents (EDTA,glycogen, citric acid or additional oxidizers like ammonium nitrate) are
usually used tomodulate the grain size and the formatof the gel. Under gelation, the particles are
linked together to form3D-network, where the physiochemical characteristic of the gel depends
on the size of the particles. Whatmakes the sol-gel method or wet-chemicalroute more useful for
the sample preparation, is the starting materials, which can be aqueous solutions or gels which
are more homogeneous and of single phase. These properties will promote the formation of a
crystalline product because the product could be formed at a low temperature and long ion
diffusion range is not required, unlike in solid state reaction. The wet-chemical route or sol-gel
method is an appropriate method for mixed salts, carbonates, sulphates and hydrated phases.
This method is perfect for a structure that does not withstand and is not stable at high
temperatures.[36, 37]
2.5.1 Hydrolysis of inorganic precursors
Usually, in the sol, the metal cation Mz+ is often introduced to water as salt, which dissolves in
water making coordination covalent bonds. In such a bonding, the positive charge of the metal
ion is diffused on the metal-oxygen bond, which results that hydrogen easily leaves the complex.
Itis generally seen that salt solutions of highly charged small cations such as FeCl3 are very acidic.
During the hydrolysis, the following equilibrium is initiated:
[ 𝑀𝑂𝐻2] 𝑧+ ↔ [ 𝑀 − 𝑂𝐻]( 𝑧−1)+ + 𝐻+ ↔ [ 𝑀 = 𝑂]( 𝑧−2)+ + 2𝐻+
Equation 4: Hydrolysis mechanism (3)
There are three different ligands presented in hydrolysis equation as following:
-Aquo: 𝑀 − (𝑂𝐻2)
-Hydroxo: 𝑀 − 𝑂𝐻
-Oxo 𝑀 = 𝑂
The key to improve the hydrolysis is by increasing the charge density of anion. However, if the
number of the hydroxo coordinated M is increased, it leads to the inhibition of hydrolysis. The
environment of the complex depends on the z charge, coordinationnumber, the electronegativity
of the metal even and the pH level of the solution.
The partial-charge model has been developed to explain the relationship between the pH and the
charge z. This model is based on, when complex is formed between two atoms charge will also
transfer resulting in each atom obtaining either positive or negative partial charge. In a binary
compound, the more electronegative element will gain more negative charge when bonded with
a less electronegative element[36, 38].

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2.5.2 Condensation mechanism in inorganic precursors
The condensation step is a nucleophilic mechanism, which depends on the coordinated metals
condition. After the substitution occurs and linkage between M1 and M2 resulting in an increase
in the coordination number of metal M2.
Olation:
Comparing different ligands is needed to understand which type of ligand exist in which type of
condition.The oxo-ligands are a great nucleophile butare a weakleaving group and are dominant
in high pH and high charge zcondition. The aquo-ligands are dominant species in low pH and low
charge z which are a great leaving group however they are a weak nucleophile. Therefore,
condensation is impossible to occur at this condition. The perfect condition for condensation
reaction is the hydroxo-ligand which is presence at intermediate pH and charge range, this
condition is creating great leaving group (O or OH) and excellent nucleophile (H2O or OH-).
Theperfectcondition forcondensationoccurswhen oneOHis coordinated toM. Differentbridges
are formed depending on the condition of the condensation. In olation condensation, a hydroxy
bridge is formed between the metals. By nucleophilic substitution SN (-ol bridge formed between
twoM atoms) and water H2O is the leaving group. The kinetics for the mechanism depends on the
electronic structure of themetal M, theelectronegativity and also on thecharge of the aqua ligand.
General rule of olation kinetics is the smaller the charge as well larger in the size the greater the
olation rate will be. The Nucleophilic substitution SN mechanism will stop when the 𝛿( 𝑂𝐻) ≥ 0.
The 𝛿( 𝑂𝐻) becomes less negative as aqua ligands (which donate electrons) are removed during
the olation condensation. The Aqua hydroxy precursor contains H2O that makes the olation
condensation more preferred than oxolation.
Oxolation:
Second condensation mechanism is oxolation, the −𝑂 − condensation bridge is formed between
the metals, whichoccurs by nucleophilic addition AN and water is eliminated from the reaction. If
a metal M is coordinated (unsaturated), the oxolation will occur by a nucleophilic addition
mechanism AN. Meanwhile if a metal M is coordinated (saturated), the oxolation mechanism will
occur by two nucleophilic substitution SN reactions between the oxyhydroxy precursors
(involvingnucleophilic addition) and followedby elimination of water from 𝑀 − 𝑂 − 𝑀.The next
step of the reaction is catalysed by creating a better leaving group which is water. The oxolation
can be preformed overa large range of pH compared to the olation, thus the kinetics are slow and
it is impossible to control the diffusion rate.[36, 39]
The gel formation is completed by dehydration of the sol-solution and it is an important step for
the gel to complete the aging (otherwise the gel can easily crack). After aging, the gel is slowly
heated up around 80°-120°Cuntil the polymeric gel is formed. Notonly pH gradient, temperature
or aging period is affecting the gelation, but also the condensation ratio and kinetics. The
distribution of the cations at the beginning minimizes the inter-diffusion of cations between the
grains. The final powder consists of very small grains and the reaction time is shorter than the
usual solid-state reaction. Thewet chemicalroute is a faster method to produces a pure and more
homogeneous sample compared to the traditional synthesis method.17,18,20

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2.6 Defect and proton transfers
Defect could be achieved by applying the imperfection to crystal system through movement of the
atom to create vacancies or impurities such as mixing two different atoms (also called doping). [12]
In oxide material, it is important forthese materials to have defectsto integrate with protons. These
type of protonic defect is a result of materials with oxygen vacancies that get filled by hydrogen H+
when they are exposed to humid environment [7, 32].
The two-main group point defect types are intrinsic and extrinsic defect. The intrinsic defect is mainly
defectsin a pure material (as Schottky-andFrenkeldefect)while theextrinsic defectis caused by impurity.
The Intrinsic defect is formed by misplacement of an atom that completes the crystal, creating a vacancy
when the atom occupies an interstitial site where no atom should be. The intrinsic defect is a high-energy
defectsince the interstitial site in solids is small or unfavourablebonding configuration.It’s important that
the target lattice is free and vacant so the atom moves freely, as known the diffusion ration on the crystal
lattice is controlled by the concentration of the vacancies. Local charge balance is destroyed during
intrinsic defect which must be restored. [40]
2.6.1 Proton transport and the mechanism in ceramic materials
The most important reaction for the formation of protonic defects is the water absorption at 600-185 °C
temperature, this mechanism requires oxygenion vacancies 𝑉𝑂
¨
. Thiscould be formed"intrinsically" which
means varying the ratio of the starting-materials (e.g. BaTi0,7Fe0,3O(3- δ)) or by extrinsically to replace an
acceptor dopant A- or B-site. Protonic defects are presented as a hydroxide ion and a proton from the
dissociation of water molecule (also called amphoteric reaction). The hydroxide ion fills an oxide ion
vacancy (actsas an acid) and the protonbinds to a lattice oxygen through a covalentbond (acts as a base).
The parameter which defines the defects environment in the perovskite could be extracted from the
equilibrium constant that is related to the created defect reaction, these defects could be expressed in
Kröger-Vink reaction as shown below:
1
2
𝑂2 + 𝑉𝑂
¨
𝐾1
↔ 𝑂 𝑂
𝑥
+ 2ℎ∙ (4)
𝐻2 𝑂 + 𝑉𝑂
¨
+ 𝑂 𝑂
𝑥
↔ 2𝑂𝐻 𝑂
.
(5)
Kröger-vink equation.
Figure 5:Different point defect a) schottkydefect and b frekel defect.[2]

13
Where two hydroxide ions OH- are substituting oxide ions (two positive charged as protonic defect 𝑂𝐻 𝑂
.
willbe formed). The hydration reaction is exothermic reaction due to the decrease in the electronegativity
of the cation (bronsted basicity of the oxide) which interact with the lattice oxygen. This means that at
higher temperature the reaction is disliked and causes dehydration. The materials with most negative
hydration enthalpies have also shown similar electronegativity for both A and B cations.
The charge defect could diffuse into the bulk of the oxide only if the oxide ion vacancies 𝑉𝑂
¨
are counter
diffused. The oxides have shown some of the oxide ions that are conducting in dry condition and have
similarity with chemical diffusion of the water. This implication is useful for oxides in fuel cells. It should
be known that not only occurrence of oxide ion vacancies during low-water partial pressure are shown
but also holes ℎ∗ appears at high-oxygen conditions.
When water vapour or the quantity of oxygen vacancy is increased according to Kröger-vink equation
(eq.4-5), this will benefit the formation of hydroxide ions and the mobile rate of the protons in the
materials. The quantity of transported protons is proportional to the conductivity i.e. as it decreases the
conductivity alsodecreases. Whenthe temperature is raised, the proton conductivity achievesa maximum
due to the mobility of the protons.
The mobility of ions is influenced by different factors like the electrostatic interaction (between the local
environment and the ion), the strain energy and the polarization of the ions in lattice. The strain energy is
the energy when ion could push through the tightly channels of the lattice, which depends on the
polarization of the ions and the free volume for the movement. [7, 12, 41]
The mechanism behind the movement of proton through an oxide is called Grotthus mechanism. The first
step is a proton rotation with a rotation mechanism or reorientation of the proton around the covalent
bonded oxygen. The second step is a jump motion to the neighbouring oxygen through oscillation
mechanism between O1 and O2 by creating hydrogen bonds. It should be known that a recent 𝑂 − 𝐻 bond
will remain until the other 𝑂 − 𝐻 bond is formed with the other oxygen ion (Fig. 8). The standard
mechanism of the proton transfer is based on the formation of new bond and followedby breaking the old
𝑂 − 𝐻 bond, this will avoid the extra needed energy for breaking up the 𝑂 − 𝐻 bond.[7]
Figure 6: Schematic illustration of proton transfer with
two steps1) proton rotation and 2) proton jump around
oxygen.[7]

14
In a recent study BaTiO3, BaCeO3, BaZrO3 were investigated and the reported results have shown that the
energetic barrier of the step for proton transfer is smallest for BaTiO3 compared to barium cerates and
barium zirconates. It is assumed that this material has higher mobility due to the rate-limitation step of
the proton transfer. The stability of the protonic defect increases in this order Titanate  zirconate 
cerate. As mentioned by Kreuer K.D[7] the choiceof theacceptordopant may have localstructure reduction
effect, which may be affecting the stability of the perovskite structure and the proton defects as well.[32]
2.7 Analytical Techniques
2.7.1 X-ray powder diffraction technique (PXRD)
To determine the crystalline structure and impurities in solid materials the most used technique is X-ray
diffraction. The diffraction pattern consists of different peaks with different intensities and positions,
usually d-spacing or2𝜃. The intensities of the peaks depend onthe sample and the method of preparation.
If peaks are not sharp and narrow that could be an indication of an amorphous sample. Crystallinity of
material can be increased by heat treatments.
The x-ray beam is targeting the sample and the reflected x-ray will be collected with a detector. As the
reflected beam completes the Bragg reflection law by constructive interference, resulting to a diffraction
pattern as the intensities are corresponding to the reflected angles, where the wavelength of the incoming
beam is equal to the reflected wavelength 𝜆. The peak intensities are proportional to the number of
electrons, which are surrounded around the atom in the plane. The constructive interaction is resulting,
when the beam is in phase with each other’s (same direction for wavelength). Cell parameters can be
determined from the position of the d-spacing, which is controlled by the unit cell values
(𝑎, 𝑏, 𝑐 𝑎𝑛𝑑 𝛼, 𝛽, 𝛾) and the peak indexing by Miller indices h, k and l. [27, 31]
Figure 7: Schematic illustration of Grotthus mechanism and different stages of building and
breaking the O-H bound .[12]

15
The constructive interference (in phase) is created at 𝑛𝜆 where 𝑛𝜆 is the same as summing the directions
(AB) and (BC) while the destructivity (out phase) is not reflected:
𝐴𝐵 = 𝐵𝐶 (6)
which could be written as following
𝑛𝜆 = 2𝐴𝐵 and 𝑠𝑖𝑛𝜃 =
𝐴𝐵
𝑑ℎ𝑘𝑙
where 𝐴𝐵 = 𝑑 × sin𝜃. (7)
The aboveshown equations willlead to Bragg’s equations or Bragg law,where the reflectedbeam must be
in phase, constructive interference:
𝑛𝜆 = 2𝑑 × 𝑠𝑖𝑛𝜃 with 𝜆 = 2 × 𝑑ℎ𝑘𝑙 × 𝑠𝑖𝑛𝜃ℎ𝑘𝑙 ( 𝐴𝐵 + 𝐵𝐶) (8)
2.7.2 Rietveld refinement
The Rietveld refinement is a technique, where the differences are measured and minimized between the
experimental pattern (observed pattern), the matched structure model pattern (the calculated pattern)
and the instrumental parameter. Using asuitable diffractometeristhe majorkey of extracting thestructure
by Rietveld refinement. To minimize the difference between the calculated and the observed intensities
for each peak equation 9 can be used. In equation 9, M is the function for the minimizing the difference,
𝑦𝑖 (𝑜𝑏𝑠) and 𝑦𝑖 (𝑐𝑎𝑙𝑐) are the observed and calculated intensities at point (𝑖) and 𝑤𝑖 is the weighting
factor:
𝑀 = ∑ 𝑖 𝑤𝑖 [𝑦𝑖(𝑜𝑏𝑠) − 𝑦𝑖(𝑐𝑎𝑙𝑐)]2 (9)
The Rietveld refinement is based on different parameters of the diffraction profile. The values for
parameters are varyinguntil the ideal set, between the observed and the calculatedintensities, is achieved.
The set consist of different parameters as unit cell parameters, site occupancies, profile parameter,
background function, atomic position etc. These parameters could be refined to obtain the ideal fit and
extracting the structure for the sample.
Figure 8: Schematic illustration of constructive reflection and how
bragg equation is related. The points represent different atoms
meanwhile the lines represent for Miller indices hkl. The spacing
between two different plane is the d-spacing, as called dhkl,[11]

16
Nowadays this technique could be used for both X-ray diffractometer as well for neutron diffractometer.
The disadvantages of using X-ray data than neutron data is the Gaussian peak shape and the modell since
the Gaussian peak shape is uncompleted and not completely pure. To fix this problem, pseudo-Voight
function will help the XRD refinement, which is a mixture between Lorentzian and Gaussian parameter.
Before starting the refinement, it is important to find a model structure as a pdf card or a cif file. The
parameters as unit cell, crystal space group, site occupancies and atomic positions (coordination system
for each atom) are completely described in these types of files. The fitting between the calculated and the
observed pattern is often calculated by two important values 𝑅 𝑤𝑝 and 𝑅 𝑒𝑥𝑝.
𝑅 𝑤𝑝 = {
Σ 𝑖 𝑤 𝑖 { 𝑦𝑖( 𝑜𝑏𝑠)−𝑦𝑖( 𝑐𝑎𝑙𝑐)}2
Σ 𝑖 𝑤 𝑖 𝑦𝑖( 𝑜𝑏𝑠)2
}
1
2
× 100% = {
𝑀
Σ 𝑖 𝑤 𝑖 𝑦𝑖 ( 𝑜𝑏𝑠)2
}
1
2
× 100 % (10)
𝑅 𝑒𝑥𝑝 = {
( 𝑁−𝑃+𝐶)
Σ 𝑖 𝑤 𝑖 𝑦𝑖( 𝑜𝑏𝑠)2
}
1/2
(11)
Where N stands for totalnumber of observations, P is forthe number of parameters that are refined and C
stands forthe number of constrains that are used in the refinement. Calculation of 𝜒2 is based on the ratio
of 𝑅wp and 𝑅 𝑒𝑥𝑝 and is an assessment of the fitting according to the following equation:
𝜒2 = (
𝑅 𝑤𝑝
𝑅 𝑒𝑥𝑝
)
2
(12)
The chi-square depends on twoparameters the collecteddata and the model forthe fitting, giving high or
low chi-square. Theobtained valuesshould be used withcautionsince they couldgive a falsefitting profile.
The background is affecting the R-values, depending on if the background is calculated approximately
through interpolation and subtracted or if the background is included in the refinement by refining
different variable for the background. What leads to a false result for the Rietveld refinement is the low
𝑅 𝑤𝑝 value, which is not correct. Large background produces a low 𝑅 𝑤𝑝, in this case large, 𝑦𝑖(𝑜𝑏𝑠) will
influence the 𝑦𝑖(𝑐𝑎𝑙𝑐) by refining the background and also leading to similar value as 𝑦𝑖(𝑜𝑏𝑠) . [42-45]
2.7.3 Fourier transform infrared spectroscopy (FT-IR)
Fourier transform infrared spectroscopy is a widely used technique where the spectra consist of
absorption or emission for all sort of samples (solid, liquid or gas). This technique is mainly used for the
identification of different functional groups in the sample. The advantage of FT-IR over the dispersive
spectrometer is the high-resolution data collection over a wide spectral range. For dispersive
Figure 9: Infrared spectrum with different absorbed region [8].

17
spectroscopy, a monochromatic light beam is shining towards the sample while in FT-IR, the sample is
shined by a light beam containing different frequencies and measure the absorption or emission of the
beam by the sample to obtain data points. The IR spectra is a spectra where the intensity of the absorbed
radiation (IR) plotted against wave-number(𝑐𝑚−1 = 𝐻𝑧/𝑐). [46],[47, 48]
With modern FT-IR spectrometers the resolution is measured at the same time, and more energy sources
can be detected faster and accurate than the old technique [8]. Non-linear molecule with N atoms have
3N-6 vibrational motion or as known normal modes as called infrared active mode. Infrared active mode
absorbs the infrared light, when there is a charged dipole moment in the molecule during the vibration.
Which means that only asymmetric vibrations are detected in this technique, not symmetric vibrations.
Functional group withpermanent dipole moment willshow strongly absorbed frequencies in IRspectrum.
[47]
The inspected region in this work is from500-4000cm-1 which is known as the mid-infrared in whichtwo
types of vibration are observed:
1) Stretching vibrations (v): which cover the changes from bond length. (see Fig. 15)
2) Bending vibration ( 𝛿): which cover the changes from bond angles. (see Fig. 15)
If twoatoms withdifferent masses m1 and m2 are bounded with an elastic spring, the bond strength which
is the springs constant 𝑘 will be described as stretching vibration and can be modelled by harmonic
oscillation. The vibration frequency relies on the bond strength 𝑘 and on the atomic masses m1 and m2.
Depending on the kind of bond requires different frequencies. The vibration frequency (𝜈) is given by the
following equation:
𝜈 =
1
2
𝜋𝑐 √
𝑚2+𝑚2
𝑚1×𝑚2
(13)
Electronegativity of the neighbouring atom, the hydrogen interaction and the environment of the atom or
group are different factors that influence the absorbed frequency. For 𝑂 − 𝐻 stretching band and atoms
with hydrogen bond, the absorbed frequency will shiftto a higher optic range (downwards) and make the
k factor weaker. What also is affecting the absorbed peak toward down shift is the mass of the atoms, the
heavy the atoms are the more the absorbed peak will shift downward.
Figure 10: Stretching and bending vibrational mode for atoms.[6]

18
2.7.4 Electrochemical Impedance spectrosopy (EIS)
The Electrochemicalimpedance spectroscopy or
AC impedance is a recent non-destructive
technique used for conductivity measurements.
The advantage of this technique is to distinguish
between dielectrochemical and electrochemical
properties of the sample. The model is presented
as an electrochemical circuit.The impedance is a
total effect of the resistance of circuit where the
unit is ohm (𝛺).
The theory behind the EIS is the type of chemical
ohm’s law for AC circuit and another law that is
essential to determine the total resistance is
Kirchhoff.
The ohm’s law is a rule for when circuitcan resist the flow of the current E.The resistance is expressed as
a ratio relating to the voltage E (in V) over current I (in ampere).
𝑅 =
𝐸
𝐼
(14)
The impedance Z consists of both imaginary and real terms, whichwillbe labelled as Z*, which is called as
complex impedance:
𝑍∗ = 𝑍′ − 𝑗𝑍′′ 𝑤ℎ𝑒𝑟𝑒 𝑍′ = 𝑅 𝑎𝑛𝑑 𝑍′′ =
1
𝜔𝐶
(15)
Therefore, both Z' and Z'' are calculated through equation given below:
𝑍′ =
𝑅
1+(𝜔𝑅𝐶)2
(16)
𝑍′′ = 𝑅
𝜔𝑅𝐶
1+(𝜔𝑅𝐶)2
(17)
ba
Figure 11: Schematic figure of impedance spectroscopy sample
holder.[4]
Figure 12: Analyzed data complex plane for parallell and series model where
a)Semi-circle is parallel-combination of R and C, b) Spike is series-combination
of R and C.

19
The A.C impedance data is analysed as a graph where the imaginary part Z* or Z'' is plotted against the real
part Z', the plotted graph is also called a complex plane. The model is the factorthat affectshow the data is
plotted in complex plane. For example, if the resistance R and the capacitance C is in series to each other,
the Z'' plotted against Z' gives a vertical linear line in the Z* complex plane, also called "spikes". This is due
to fixed value of resistance R and the reduction of Z'' with increasing of Ω (see Fig.17(b)). For parallel RC
circuit systems, the plotted graph is a semi-circle in the Z* as shown in fig 17a. The intercept of the semi-
circle is on the Z' plane from zero to R and the maximal of semi-circle occurs at:
𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 = ω𝑅𝐶 = 1 where the maximum of semicircle = 𝑅/2 (18)
It is also possible to obtain two or three semi-circles at Z* complex plane. This observation will be due to
the bulkresistance Rb, bulkcapacitanceCb, grain-boundary resistance Rgb, grain-boundary capacitanceand
Cbg where the total resistance is a sum of bulk and grain-boundary contribution. It's important to
understand that each point on spike or semi-circle corresponds to a specific frequency value, the reason
why it is also important to scan a range of frequencies to produce the complex graph. It is impossible to
distinguish if the plotted data is a spike or a semi-circle complex plane plot with only one frequency value.
The graph is then plotted (Z’’ against Z') by simple method where the variable is adjusted for both
resistance R and capacitor C at each null (ν) point (frequency point). The complex plane diagram makes
it easy to plot variables against each other. [27]
2.7.5 Scanning electron microscopy (SEM)
Scanning electronmicroscopy (SEM) is a microscope that uses electrons
instead of light for the formation of an image. SEM is a technique with
different advantages for studying the surfaces of powders, solids and
their topography. High resolution, micrometre zooming,can be achieved
by the depth focuswhich results in 3D images. SEMis a technique where
the thickness is no problem since the beam pierces through the surface.
Additionally, the background scattering can be minimized to obtain a
higher resolution images.
Forthe reflection mode of operation, the sample preparation is often not
needed. Low electrochemical conductivity can be solved by sputtering
the sample with a thin layer of conducting material. The thin metal layer
over the surface prevents the build-up of charge on the sample surface
and increases the conductivity of the surface.
In whichevermode of operation, transmission orreflection, the material
composition is shown by contrast. The BSE (back scattering electron
mode) images are showing material composition by contrast. The mode
is based on backscattering coefficient,whichincreases when the atomic
number increases, heavier materials will be white and lighter materials
willbe blackin the images. Theexposed sample surface is gold sputtered
with an acceleration voltage of up to 15-20 kV.The differedelectron beam fromthe sample generates two
different types of collisions from the backscattered electrons: in-elastic scattering from electron-electron
collisions and elastic scattering from electron-nucleus collisions. The secondary electron is used to detect
and study micro-structural information such as grain growth and grain size
SEM has been used in conjugation with Energy dispersive spectroscopy (EDS) whichis a technique
used to identify whatkind of elements are and their relative proportions (i.e. Atomic %) in the
sample.[27] [3]
Figure 13: Schematic illustration for SEM
instrument.[3]

20
2.7.6Thermogravimetric Analysis (TGA)
Thermogravimetric analysis is a technique used to
study the mass changes during temperature
changes (heating or cooling) as well the physical
and chemical properties of the sample. The
observed graph is a function of temperature
plotted against mass-loss for the specimen:
function ∆𝑚 = 𝑓(𝑇, 𝑡),where T is the temperature
and t is the time. The sample could gain or lose
mass depending on thecontrolled atmosphere and
used gas.
Analysing the data and how themass of the sample
is affected by the heat provides different types of
information like; the decomposition of the
product, the thermal stability, the kinetics and the
activationenergy of the decomposition.A general decomposition mechanism can bedescribed as the initial
sample A breaks down at certain temperature T and yields at least two products B and C. At least one of
the products B or C is a volatile substance, which will completely vaporize and result in a mass loss.
Depending on the elements, the reaction could be endothermic, where heat is absorbed or exothermic
where heat is released.
𝑎  𝑏𝐵 + 𝑐𝐶 (19 )
Evaporating the product occursin several steps and the first substance to leave is oftenwater particularly
for n-hydrous samples (around 100°C). The gas atmosphere have a major influence on the sample e.g. if
the gas is inert with constant flow of nitrogen N2 gas or argon gas leading to a protection of the sample
from any oxidation or reduction as it will resulted as mass gain or loss in the plotted graph. [49, 50]
Figure 14:Schematic illustration of TGA instrument(NETZSCH
TG 209F1 Libra).[10]

21
3 Methods
3.1 Sample preparation
All samples have been synthesized through twodifferent methods: solid state reaction and wet-chemical
route (sol-gel method). Different synthesizing methods were used to figure out the suitable method for
the synthesis of pure materials. Different sets of experiments were based on different acceptor-iondoped
BaTiO3 (indium, iron & scandium) specifically focusing on the two-different doping ratio x1=0,17 and
x2=0,33. The final sample composition will be 𝐵𝑎𝑀0,17 𝑇𝑖0,83 𝑂(3−𝛿) and Ba𝑀0,33 𝑇𝑖0,67 𝑂(3−𝛿), and all
samples were given shorter names like: BTI17, BTI33, BTF17, and BTF33 (see abbreviation list).
3.1.1Solid state reaction
The samples were synthesized by traditional solid-state reaction where stoichiometric amounts of the
starting materials barium carbonate BaCO3 (Alfa Aesar, 99.8%), titanium oxide TiO2 (Aldrich, 99.8%), iron
oxide Fe2O3, scandium oxide Sc2O3 (Alfa Aesar, 99.9%) or indium oxide In2O3 (Alfa Aesar, 99.9%) were
weighed and grinded for 20-30 min together with ethanol in an agate mortar. Ball-milling was excluded,
which is the main problem causing impurities and the contamination ratio increased as the ball-milling
was used. The powder was calcinated at 1000°C for24h in alumina crucible, after the calcination step, the
powders were grinded again and pressed into a pellet using a manual pressure (16 mm, first press to 3-
ton and second press to 7-ton). The samples were re-fired, re-grinded after each heat-treatment until the
pure sample was obtained. The table below is showing all samples different temperatures (heat
treatments). All samples were analysed with PXRD analysis to check the purity level.
Sample Calcination temp. SR. final temp.
BTF 17 1000°C/24h 1250°C/24h+stepcooling 750°C/6h
BTF 33 1000°C/24h 1253°C/10h+stepcooling 750°C/6h
BTI 17 1000°C/12h 1350°C/25h
BTI 33 1000°C/12h 1350°C/42h
BTS 17 1000°C/12h 1455°C/24h
BTS 33 1000°C/12h 1405°C/14h
Tabell 1: Sintering temperature for all sample in the ceramic method.

22
3.1.2Wet chemical route (sol-gel method)
The samples BaMxTi(1-x)O(3-δ) were also synthesized through wet-chemical route (sol-gel method). Since
the starting materials were acetate precursors, that is the main key to form a gel without additives like
ethylene glycol and citric acid[51].
Depending on which acceptor-doped BaTiO3 was synthesized, both barium acetate and the dopant
precursors were dissolved in acetic acid and diluted water followedby heating the mixture to dissolve all
particles. It is important to separate the barium-metal ion solution and titanium ion solution. As shown in
Fig.20, the first solution A was prepared by dissolving barium acetate and metal (indium or iron) acetate
in acetic acid and diluted water in a pyrex beaker. The mixture was also heated up to 80°C to improve the
dissolving ratio of the starting materials. The next solution (titanium solution) was prepared by using the
following procedure (solution B), first 40 ml of ethanol was added to a pyrex beaker. A stoichiometric
amount of titanium isopropoxide was added to the ethanol and stirred for 30 min. In solution A, barium
and metal ion solution were added to titanium isopropoxide drop wise. To control the drop speed, a
peristaltic pump has been used overnight and the speed that was used was 1,0 – 1,15 rmp.
The gel formation was completed by aging, followedby a dehydration of the sol-solution allowing enough
aging time is an important step for the gel to be completed otherwise the gel can easily crack. After the
aging, the gel did becomethickerthen more vividandslowly heated up at80°C to150°C until thepolymeric
gel is formed.Depending on whichsample wasprepared differentaging periods wereneeded. For example,
the indium doped BaTiO3 was aged overnight and the iron especially the higher ratio needed more aging
period (almost 3 days). The xerogel was pre-heated from 300°C-800°C (see table 2) in order to evaporate
and decompose all organic compounds, however,it is also important to achievea crystalline nanopowder.
In the final step of sintering, the nanopowder was pressed into a 16-mm pellet under pressure 3 MPa – 7
MPa viaa uniaxial pressing and heated in an alumina boat up to the final heat-treatment. The distribution
of cation at the beginning is the key to minimize the inter-diffusion rate of the cation between the grains.
The final powder consisted of very small grains and the reaction time was shorter than the traditionally
solid-state reaction.
Figure 15: Schematic figure for wet chemical route (sol-gel) experiment.

23
Table 2: Heat-treatment for wet-chemical route during synthesis.
Sample 1° S.R 2° S.R 3° S.R 4° S.R
BTF 17 300°C /24h 400°C/8h 800°C /10h 1250°C/18h +step- cooling 750°C/ 6h
BTF 33 300°C /24h 400°C/8h 800°C /10h 1250°C/18h +step- cooling 750°C/ 6h
BTI 17 300°C /24h 400°C/8h 800°C /10h 1350°C/27h
BTI 33 300°C /24h 400°C/8h 800°C /10h 1350°C/24h
3.1.3 Vacuum drying and protonation of the samples
3.1.3.1 Vacuum drying the sample
During the cooling from high sintering temperature for as-prepared sample, it is known that uptake of
water is possible under these conditions (partial humid atmosphere). The vacuum drying method is used
to get rid of the water molecules in the samples. The samples are dried at 950°C for 35 h in vacuum of
10-5 to 10-6 mbar.
3.1.3.2 Protonation of the sample, Hydration method
As-prepared samples were exposed to humid atmosphere in order to hydrate the sample and fill the
oxygen vacancies.The protonationlevel reaches to the maximum under 300°C-185°C and the experiments
were done as shown in fig(Fig.21). The powderswere placed in the furnace with a decreased temperature
from 600°C to 150°C. For each temperature step the duration was minimum 2h, except for 300°C where
the powder was exposed for 24h and at 185°C for 3 days. Argon gas have been pre-saturated with water
at 70°C during the experiment.
Figure 16: Schematic figure of setup for hydration experiment.[1]

24
3.2 Characterization methods
3.2.1 X-Ray powder diffraction (PXRD)
X-ray diffraction measurements were performed for all samples in order to check the purity after each
heat-treatment step and also to extract a longer data scan for structure studies (Rietveld refinement). D8
Vario Advance Diffractometer (Bruker AXS) was used to extract the measurements where the D8 uses a
copper as X-ray source and germanium monochromator to extract Cu-Kalfa1 with λ= 1,5406Å.
For regular impurity checkof the sample, the scan run was a 32-min scan in the 2θ angle between 20°-65°
and 0,025° as step-size. While for the Rietveld refinement was a longer scan (8h) has been performed to
obtain a high-quality data, in 2 θ between 15°-110° and 0.019 as step-size.
The Rietveld refinement was performed on four samples BTF 17 (SSR), BTF 33 (WCR), BTI 17 (SSR) and
BTI 33 (WCR), where Topas has been used as a refinement software. Programme Diamond was used to
visualize the structures that have been extracted from the refinement of each sample.
3.2.2Scanning electron microscopy (SEM)
SEM was performed on the surface and the cross-section of BTF 17 & 33 and BTI 17 & 33 pellet, using Leo
Ultra 55 FEGSEM withenergy dispersive X-ray spectroscopy EDS OxfordINCA. For BTF33 and BTI33 the
acceleration voltage was 15-20kV. The BTF17 (SSR) and BTI 17 (WCR) imaging was performed with
Phenom World (PRO X) with accelerating voltage 15kV and element dispersive x-ray dispersive (EDS).
3.2.3Electrochemical impedance spectroscopy (EIS)
The impedance spectroscopy was measured by ProboStat measurement cell from NorECs, which was
connectedto Solartron 1260 impedance spectrometer. By using the Smart softwarefordata collectionand
later on refining the data by Z-view software and useful results were obtained. The measurements were
performed on 7 mm pressed pellet forBTF 17 (SSR), BTF33 (WCR), BTI 17 (WCR) and BTI 33 (SSR). The
inner diameters (around 5mm) wereplatinum covered firstly by sputtering and secondly by platinum ink
(Metallor, UK) to create the electrodes. Beforestarting the measurements, the platinum-coating was dried
at 850-950°C for 3 h. The platinum electrodes were approximately 0,136-0,212 cm2 as area and was used
to extract a good resistance. The data was measured under a temperature range of 850°C-150°C with a
frequency range of 100 MHz-6MHz under different atmospheres Dry/Wet N2 and synthetic air.

25
The Z-view software was used to refine and fit the measured data with a model (Fig. 22). The refining
model was used to represent the electrical response from the sample where each data point (at each
temperature) was refined by a parallel combination of the resistance (R) and the constant-phase element
(CPE). Depending on the analysed sample, the resistance at the low temperature range (under 400°C)
could not be reliable due to the high impedance. It was possible in some cases to see three semi-circles
which correspond to the bulk (10-10-10-12 F/cm), the grain (10-8-10-10 F/cm) and the electrode (10-5-10-7
F/cm) responses. However, the most common semi-circles are only for the bulk or bulk with grain which
is represented as total resistance or as called total conductivity.
3.2.4 Thermogravimetric analysis (TGA)
The thermogravimetric analysis was performed on as-prepared and hydrated samples BTF 17 (SSR) & 33
(WCR) and BTI 17 (WCR) & 33 (SSR) by NETZSCH TG 209F1 Libra instrument. Around 20-30 mg of the
sample wasplaced in alumina crucibles foreach TGArun. The experiment was running under nitrogen gas
with a flow of 20 ml/min as in and 25 ml/min as the exit gas. The samples were heated up from room-
temperature to 950° for all samples. Before starting the measurements, an empty crucible run was
preformed (referencefile) touse as correctionfileand calculating the differencebetweenthe cruciblewith
sample and the empty crucible.
3.2.5 Fourier transform infrared spectroscopy (FT-IR):
The Fourier transform infrared spectroscopy (FT-IR) was performed on Nicolet 6700 FT-IR instrument
for hydrated and vacuum dried samples. The experiments were performed at room-temperature and in
the air. The samples were placed in a micro-sample holder for the measurements where the background
spectra were collected with optical chemical transparent 𝐾 − 𝐵𝑟 (Potassium bromide) as a reference
sample and subtracted from the real data measurements. The experimental configuration was performed
in the optical chemical range of 4000cm-1 to 400cm-1 with 2cm-1 as a resolution for the peak. This analysis
technique has been used to find broad 𝑂 − 𝐻 stretching in the vibrational band in the infrared spectrum.
The 𝑂 − 𝐻 stretching band range is between 2500-3500 cm-1.
Figure 17: Impedance spectroscopy semi-circle refined data.

26
4 Results
This section includes all results and the data extracted fromall characterization techniques that have been
mentioned in the method second. Inthis section only results willbe presented but willbe discussed in the
receding section.
4.1 Iron doped BaTiO3
4.1.1 X-ray powder diffraction (PXRD)
The samples were analysed by XRD after each heat-treatment, starting after the second heat-treatment to
check the impurity level and progress for each sample. The BTF 17 (SSR) synthesised through the solid-
state reaction (sintered at 1250°C for 24h with step-cooling at 750°C for 6h) adapted a hexagonal
structure. The perovskite phase and purity was developed at 1200°C (blue) by increasing the temperature
whichis visible in Fig. 23. The (red) pattern belong to the case whentemperature was 1250°C for24h with
step-cooling at 750°C for 6h, the (blue) pattern temperature was 1250°C for 18h with step-cooling at
Figure 18:XRD diffractogram with different temperature sintering for BTF 17 SSR, where the
(black) pattern is for the pure sample and the (purple) pattern is after the first calcilation
reaction.

27
750°C for6h and the (purple) pattern temperature was 1250°C for18h with step-cooling at 750°C for6h
After the step-cooling, which is just a cooling step at 750°C for 6h, the reaction is followed by a cooling
down step from 750°C to room-temperature.
The BTF 33 (WCR) was synthesized through the wet chemical route and subsequently the sample was
sintered at 1250°C. The xrd for BTF 33 was collected after the last sintering temperature, which has
similar xrd evolutionas BTF17. The first sintering temperature was 400°C for2h, 800°C for10h and was
followed by final sintering temperature1250°C for 18h with step-cooling 750°C for 6h (and to room
temperature). As seen in Fig. 24, the perovskitephase wasobtained after one sintering temperature and
the sample was completely pure.
The Rietveld refinement has been performed forboth BTF 17 (SSR) and BTF 33 (WCR) with TOPASand
the structures have been visualized by Diamond software. Both samples have adopted a hexagonal
structure withspace group P63/mmc.The unit cellvolume forBTF 17 (SSR) was refined as V=397,602Å3
(7), where the cell parameter was a=5,73 (4) Å and c=14,023 (16) Å. The ratio between Rexp and Rwp,
whichis determined as chi-square χ2 is equal to 2,57%. The crystal density was also calculated by Topas
as 𝜌 𝐶𝑟𝑦𝑠𝑡𝑎𝑙= 6,059 g/cm3. The cell parameters for BTF 33 (WCR) were a=5,72 Å (14), b=14,03 Å (4),
where the volume is 397,195 Å3 (18) and the crystal density is 5,917 g/cm3. The chi-square χ2 was
calculated and is equal to 3, 47%. For more information regarding the bond-length, Rwp, Rexp and the
occupancies, a full description table is included in the discussion section (table 5).
Figure 19:XRD diffractogram with final sintering temperature for BTF 33 wet.

28
Figure 20:Rietveld Refienemnt and structure for BTF 33(WCR), where the observed data
in(blue), the calculated data in (red) and the difference line in (grey). Ba atoms (blue), Fe
atoms (green) and O atoms (red).

29
Figure 21:Reitveld refinement and structure for BTF 17, where the observed data in(blue),
the calculated data in (red) and the difference line in (grey). Ba atoms (blue), Fe atoms
(green) and O atoms (red)

30
The BTF 17 (SSR) as-prepared sample has shown -0,12% as a mass loss and the hydrated sample has a
higher mass loss -0,58% (see Fig.28). At temperature 400°C, the hydrated sample showed more mass
loss compared to as-prepared sample. The percentage of mass loss calculation was from room-
temperature up to 750°C. For BTF 33 (WCR) sample, the hydrated sample showed a higher mass loss
(-1,70%) compared toas prepared (-1,21%) sample. The different stages of mass loss wereobserved for
BTF 33 (WCR) Fig.27 that is common for samples prepared via wet chemical route. The measurements
for as-prepared and hydrated samples have been collected in different occasions with two different
background correction files.
The infrared spectroscopy was used in order to study the 𝑂 − 𝐻 stretching band vibration in vacuum-
dried and hydrated samples. All peaks in the range of 500-1500 cm-1 will not be explained since it’s the
finger print region and it’s a unique region for each sample as finger print or DNA. The vibration mode
that is detected around 3000 cm-1 indicates the presence of for 𝑂 − 𝐻.For BTF17 (SSR) the vacuumdried
sample did not show any signal forOH group whilehydrated sample did showed signal at 3000 cm-1. For
BTF33 (WCR), similar behaviour wasobserved exceptthat the vacuumdried sample also showeda small
contribution from O-H stretching band as shown in Fig.30 as well Fig. 29.
Figure 23: TGA data for BTF 17 (SSR) for as-prepared
(brown) and hydrated sample (blue).
Figure 22:TGA data for BTF 33 (WCR) for as-prepared (purple)
and hydrated sample (light blue).

31
4.1.5 Scanning electron miscroscopy (SEM)
The scanning electron microscopy was applied to the BTF 17 (SSR) and BTF 33 (WCR) to study the
microstructure and the grain-boundary size. As seen in pictures below (Fig.32), BTF 33 (WCR) shows a
denser micro structure with a grain size approaching around 2-4µm compared to BTF 17 (SSR) with
average grain size of 2-8,3µm Fig.31, while at 8µm both samples have shown denser and lower poor
structures. The grain-boundary size varied between small and large ones for both samples. BTF 33
(WCR) images were collected by Leo Ultra 55 FEG SEM and BTF 17 (SSR) images was collected by
Phenom World (PRO X).
Figure 24:Infrared spectra for BTF 17 (room-temperature).
Figure 26: SEM images for BTF 17 (SSR).
Figure 25:Infrared spectra for BTF 33 (room-temperature).

32
The element identification was performed for both samples to check the atomic ratio and compare them
with the calculated values. The BTF 33 (WCR) has shown a lower atomic ratio of iron in the sample and
was synthesised through wet-chemical route. Since, iron is a “hard-ion” there is limitation of iron ion
transport within the synthesized materials (check discussion). The lower substituted iron sample (BTF
17), which was synthesized through solid state reaction, showed a slightly higher atomic weight
percentage compared to the calculated one (17%). The denser sample in iron doping samples was BTF33
(WCR) compared to BTF 17 (SSR), from the calculations of relative density (Appendix B) and also
confirmed by SEM images.
4.1.6 Electrochemical impedance spectroscopy (EIS)
Firstly, the raw data were refined for each temperature using z-view to extract the resistance. The total
resistance was calculated by adding the grain and bulk resistances (R1+R2) and followedby calculating
the conductivity (𝜎).As shownin figure 33, the conductivity isshowing a p-type electronic behaviour for
BTF 17 (SSR) sample, since the total conductivity is increased from dry N2 < wet N2 < dry air < wet air.
All data were collected during cooling down conditions. The wet condition gave a high conductivity in
both high and low temperature range. The highest conductivity was obtained in wet air at 450°C with
conductivity (𝜎) = 1,53 × 10−3 Scm−1. The material did not conduct well with both dry/wet nitrogen
and the conductivity did increase at wet synthetic air condition. As seen in Fig. 33 the wet nitrogen has
the highest activation energy and the lowest activation energy is at the highest conducting condition
which is wet air Ea=0,39 eV.
Element Atomic
Weight%
Ba 40,62
Ti 41,1
Fe 18,3
Table 1:EDS analysis BTF 33.. Table 2:EDS analysis BTF 17.
Figure 27:SEM images for BTF 33 (WCR)

33
The BTF 33 (WCR) (Fig.34) also show a high conductivity at wet synthetic air condition due to the
protons in the sample. For 150-300°C at the dry air condition a lower conductivity while in the wet air
condition conductivity did increased by half magnitude. At a higher temperature range the wet and dry
air conductivity was almost the same. Both BTF 17 (SSR) and BTF 33 (WCR) did show a lower total
conductivity atwet and dry nitrogen compared tothe air condition. BTF33 (WCR) showed the following
trend; dry N2 < wet N2 < dry air < wet air which indicates for a p-type behaviour. The highest total
conductivity was observed at 350°C for wet air condition where the conductivity was 𝜎 = 1,56 ×
10−3 𝑆𝑐𝑚−1 (550°C 𝜎 = 5,62 × 10−3 𝑆𝑐𝑚−1). All activation energy values are shown in the Arrhenius
plot, wherethe highest activationenergy is fordry nitrogen Ea=0,556eV and the lowest activationenergy
for dry and wet air Ea=0,314-0,32 eV.
4.2 Indium doped BaTiO3
4.2.1 X-ray powder diffraction (PXPD)
The XRDwasperformed after eachheat-treatment starting after 300°C(second heat-treatment) to check
the evolutionand the progress of eachsample. ForBTI17 (WCR) as shownin diffractionpattern (Fig.35),
at 800°C for 10h (red) the sample changed the phase from amorphous to more crystalline phase. By
increasing the temperature slightly fromcalcinationstep (blue), the perovskite structure was sintered at
1350°C (green+magenta). The sample did show some impurity peaks at low 2𝜃 whichwere successfully
removed by vacuum drying followed by another heat-treatment at same temperature as previous
(magenta).
Figure 28:Plotts of total conductivity against 1/T for as-prepared BTF
17(SSR), measued in dry/wet nitrogen and synthetic air.
Figure 29:Plotts of total conductivity against 1/T for as-prepared BTF 33(WCR),
measued in dry/wet nitrogen and synthetic air.

34
BTI33 (SSR), whichwassintered through solid state reactionat 1350°C where the finalperovskite phase
is shown as pure phase (blackpattern). Theperovskite structure and the crystallinity improved afterthe
first heat-treatment step (calcination step blue pattern) at 1200°C for 24h (red). By increasing the
temperature slightly to1350°C, the lowestintensity peaks at 2𝜃 of 22, and 50° improvedin the sharpness
and the pure phase was achieved at 1350°C for 27h (black) (see Fig.36).
Figure 30:XRD diffractofram with different temperature sintering for BTI 33 SSR,
where the pure perovskite phase (black) and calcination pattern after first reaction
(blue).
Figure 35::XRD diffractofram with different temperature sintering for BTI 17 WCR, where the
pure perovskite phase (purple) and calcination pattern after first reaction (blue).

35
The Reitveld refinement was performed for both BTI 17 (WCR) and BTI 33 (SSR) using TOPAS and the
structure was visualized by Diamond. For BTI 17 (WCR) 1,32% of In2O3 impurities have been detected in
the sample. Both sample have adopted a cubic structure (see Fig. 37) and the space group was Pm3m.
The cell parameter a = 4,106 (3) Å for BTI17 (WCR) and a=4,104 (3) Å forBTI 33 (SSR). The calculated
volume using cell parameters, for BTI 17 (WCR) V=69,224Å3 and BTI 33 (SSR) V=69,123 Å3. Using
TOPAS,the crystaldensity has been calculatedas; forBTI 17 (WCR) the density is 𝜎 = 6.08600 g/cm3 (8)
and for BTI 33 (SSR) it’s 𝜎 = 6,07337g/cm3 (8). The ratio between Rexp and Rwp, whichis determined as
the chi-square χ2 is equal to 2,67% for BTI (WCR) and 2,54% for BTI 33(SSR). For more information
regarding the bond-length, Rwp, Rexp and the occupancies a full description table is included in the
discussion section (table 5).

36
Both as-prepared and hydrated samples were investigated, the hydrated sample showed a higher mass
loss percentage than the as-prepared sample. For the BTI 17 (WCR) as-prepared sample showed -0,16%
mass loss and the hydrated sample -0,56% (see Fig. 39). For the solid state sintered sample BTI 33 (SSR),
the mass loss for both as-prepared (-0,72%) and hydrated sample (-0,85%) is shown in Fig.38. The
hydrated samples had more mass loss than as prepared one (150-300°C) and the as-prepared samples the
mass loss is proportional to the temperature.
Figure 33:TGA data for BTI 17 (WCR) for as-prepared (black)
and hydrated sample (red).
Figure 32:TGA data for BTI 33 (SSR) for as-prepared (green)
and hydrated sample (purple).
Figure 31:Reitveld refinement and structure for BTI 17 (WCR) & 33 (SSR), where the observed
data in(blue), the calculated data in (red) and the difference line (grey). Ba atoms (white), In
atom (purple) and O atoms (red).

37
Starting with BTI 17 (WCR) which did not show broad peak at 3000 cm-1 for hydrated sample (a small
contribution of OHbond), however for the vacuum-dried sample a broad bump is showed in same region
(Fig.41). When the dopant ratio is increased BTI 33 (SSR) a clear broad peak did appear at 3000cm-1 for
the hydrated sample and the vacuum-dried sample is almost straight.
4.2.5 Scanning electron microscopy (SEM)
The scanning electron microscopy was applied on both BTI 17 (WCR) and BTI 33 (SSR) to study the
microstructure and the grain-boundary size. Thegrain size forBTI 33 (SSR) is around 2-10µm compared
to BTI 17 (WCR) around 1-3 µm, as seen in images bellow the grain-boundary size is varying between
small and large ones.
Figure 35:Infrared spectra for BTI 17 (room-temperature).
Figure 36:SEM cross-section images for BTI 33 (SSR).
Figure 34:Infrared spectra for BTI 33 (room-temperature)

38
The element identification has been performed for both samples to check the atomic ratio and compared
them with the calculated ratio. The BTI 17 (WCR) has shown slightly higher atomic ratio 18% which was
calculated to be 17%. The higher substituted indium sample, which was synthesized through solid state
route, has shown low atomic ratio ~16% which supposed to be 33 %. This is common in solid-state route
due to the high temperature as well long sintering period. From the calculations of relative density
(Appendix B), the denser sample is BTI 17 (WCR) > BTI 33 (SSR), 98.55% which is confirmed by SEM
images.
4.2.6 Electrochemical impedance spectroscopy (EIS)
As shown in Fig 44 and 45, the Arrhenius plots are for both samples BTI 17(WCR) and BTI 33 (SSR) are
adapting the plateau effect. As shown in Fig.44 the conductivity is similar for all conditions of BTI 33
(SSR) from450°C until 850°C. At 200°C the wetair conditionshows the highest conductivity 𝜎 = 9,98 ×
10−3 𝑆𝑐𝑚−1 whichis twoorders larger than thedry air atmosphere. Dueto time scale BTI17 (WCR) was
not possible to run wet/dry synthetic air. The highest activation energy has shown for dry nitrogen and
air; however, the lowest activation energy has shown for wet condition specially wet air (150-300°C)
condition.
Element Atomic
Weight %
Ba 40,62
Ti 41,1
In 18,3
Table 4:EDS analysis for BTI 17 (WCR).Table 3: EDS analysis for BTI 33 (SSR).
Figure 37:SEM images for BTI 17 (WCR).

39
5 Discussion
5.1 Structure
5.1.1 Hexagonal
The BTF 17 (SSR) and the BTF 33 (WCR), both ratios are adapting hexagonal structure. The space group
is P63/mmc and is described as the 6H-BaTiO3[52]. the 𝑇𝑖/𝐹𝑒(2) − 𝑇𝑖/𝐹𝑒(2) occupy the face sharing
octahedron and 𝑇𝑖/𝐹𝑒(1) − 𝑇𝑖/𝐹𝑒(1) occupy the corner sharing octahedron. The bond length for BTF
33 (WCR) 𝑇𝑖/𝐹𝑒(2) − 𝑇𝑖/𝐹𝑒(2) is 5,718 (8) Å and 𝑇𝑖/𝐹𝑒(1) − 𝑇𝑖/𝐹𝑒(1) is 2,726 Å (see Fig.46).
The 17% substituted titanium, distance of 𝑇𝑖/𝐹𝑒(1) − 𝑇𝑖/𝐹𝑒(1) is 2,698 (14) Å and of 𝑇𝑖/𝐹𝑒(2) −
𝑇𝑖/𝐹𝑒(2) is 5,722 (8) Å. In a comparison of the distance between the two ratios, increasing the ratio of
the substitution will lead to a longer bond-length for both 𝑇𝑖/𝐹𝑒(1) − 𝑇𝑖/𝐹𝑒(1) and𝑇𝑖/𝐹𝑒(2) −
𝑇𝑖/𝐹𝑒(2), and this result was as expected. The metal facesharing octahedron bondstabilize the structure
and will be stronger than the metal repulsion energy. This is the main reason for the creation of oxygen
vacancies. Rietveld refinement showed that, the oxygen vacancies are created at O2 layer which is the
corner shared octahedron oxygens. The cellvolume of the hexagonal decreases slightly when the ratio of
Fe3+ was increased. The expansion in the unit cell as well the bond length in facesharing octahedron was
excepted since the ionic radius of Fe3+ is 0,690Å compared to 0,605 Å for Ti4+.
Figure 39: Plotts of total conductivity against 1/T for as-prepared BTF
17(WCR), measued in dry/wet nitrogen and synthetic air.
Figure 39: Plotts of total conductivity against 1/T for as-prepared BTI
33(SSR), measued in dry/wet nitrogen and synthetic air.
.

40
5.1.2 Cubic
The Indium doped BaTiO3 samples are adapting a cubic structure with the space group Pm3m, and there
was no evidence for expanding the unit cell when the doping ratio was increased. The unit cell volume
did reduce by 0.101 Å3 when the ratio was increased. From the structure, it is shown that the cubic
structure is Ti and In at A-site, disordered perovskite. From VESTA, the calculated bond-length for BTI
17 (WCR) was 2,053 Å (Ti1/In1-O1) and for BTI 33 (SSR) was 2,052Å (Ti1/In1-O1).
5.2 TGA & FT-IR
From the stoichiometric chemical formula BaMxTi(1-x)O(3-δ), the oxygen occupancies were calculated as
maximum 2,92 for 17 % and 2,83 for 33 % in the vacuum dried samples. Based on the kröger-vink
equation, the vacancies are filled with the hydroxyl groups (OH-). The TGA results provide information
Table 5:Summery from reitveld refinement for BTF 17&33 and BTI 17&33.
Figure 40:Ordering of atoms in hexagonal structure for both
BTF17 & 33.

41
about hydrogen concentration in all samples. All samples were heated up from room temperature to
950°C and the mass loss starts around 200°C, the TGA results confirmed that a significant number of
protons are present in all as-prepared samples. The hydrated samples which were hydrated at 185°C
revealed 76,29% (BTF33), 92,83% (BTF17), 91,71% (BTI17) and 68,45% (BTI33) (Appendix B).These
results indicate that BTF 17 (SSR) has the highest energy level compared to other samples. The order of
oxygen vacancies is as following: BTF 17 (SSR) > BTI 17 (WCR) >BTF 33 (WCR) > BTI 33 (SSR). After
700°C the signal is showing more mass loss for almost all hydrated samples. After the TGA experiments,
all samples change colourfromdark to light. The iron doped samples change the oxidation state from 2+
(dark colour) magnetite (Fe3O4) to 3+ (light colour) and hematite (Fe2O3) the most stable structure is
hematite[53]. The BTF 33 (WCR) was synthesized through wetchemical route; this material tends to lose
mass as seen in the Fig.27). It’s also showed that the mass-loss for BTI 33 (SSR) and BTF 33 (WCR)
samples starts below 100°C whichcouldindicate waterloss fromthe structure. Another property forsol-
gel synthesised materials is that they tend to be more hydrophilic and they gain water easily from the
atmosphere which is resulting in the strange TGA curve. Since the starting materials for wet chemical
route are carbonates, sometimes they are hard to be removed from the sample and are easy to re-
carbonate until 1400°C. It should also be mentioned that some impurities have been detected for BTI17
(WCR) and BTF 33 (WCR) which could be affecting the results.
The IR results are also confirmingthe presence of O-Hband in all samples in the infrared spectrum range
(3000cm-1), for both hydrated and vacuum-dried samples. As known the vacuum dried samples should
not show a broad O-H peak, but BTI 17 (WCR) did show OH vibrational stretch mode. For BTI 33 (SSR)
and BTF33 (WCR), they showed a small peak in the infrared region. The BTF 33 (WCR) shows a narrow
peak at around 3650 cm-1 for the non-hydrogen bonded watermolecule[54]. From all samples, the BTF33
(WCR) shows the broadest peak (hydration percentage 92,83%) compared to other samples.
5.3 Conductivity
At around 400°C, conductivity of BTF 17 (SSR) is one magnitude higher than BTF 33 (WCR) in wet air
condition. Unfortunately, the same comparison is impossible to be done for BTI 17 and 33 samples, due
tothe lackof data forBTI17 (WCR). The highest conductivity showsforBTI33 as 𝜎 = 9,98 × 10−3 𝑆𝑐𝑚−1
Figure 42:Infrared spectra for all vacuum-dried samples (room-
temperature).
Figure 42:Infrared spectra for all hydrated samples (room-temperature).

42
at low temperature comparing this value at the same temperature, the hexagonal structure BTF 33
(WCR) shows a lowerconductivity 𝜎 = 3,85 × 10−4 𝑆𝑐𝑚−1whichisindicating the mobility of the protons
in the hexagonal structure is not favourable. The activation energy is an energy level that needs to be
achieved for conductivity to take place and the lowest activation energy is preferred.
The total conductivity for BTF samples increased as follows; Dry N2<Wet N2<Dry air<Wet air. This
order is known for p-type semiconductors. At 350°C in wet air condition, the total conductivity for BTF
17 is two orders of magnitudes higher compared to the total conductivity in dry air condition indicating
that the dominant charge carriers are protons (Proton conducting material). At 300°C for BTF 33, the
total conductivity in wet air is one magnitude higher than the total conductivity in dry air. The indium
33% doped sample did show a plateau-effectwheretheconductivity isthesame inthe temperature range
450-850°C[7]. This effect is showed in other samples like (BaZr(1-x)MxO3-δ (M=In and Yb)[21, 25, 55] and
BaTi0,5In0,5O3- δ [16]). This is due to the decrease of the concentration for the charge carries (protons) also
due to an increase in the mobility of the remained protons.
The difference in the conductivity also depends on the structure (6H hexagonal and cubic). This has a
main input from the number of hydrogen present in the structure. The protons are located near the O1
plane of the face sharing octahedron in the hexagonal structure. For the cubic structure, the protons are
disordered overeach edge and the mobility increases[17]. The low conductivity inthe hexagonal structure
is due to the low symmetry compared to the cubic structure. In the hexagonal structure, there are two
different oxygen vacancies where the protons could be trapped and difficult to be removed from the
structure. A general rule forthe conductivity is the highest symmetry willleads to a larger cell volumeas
well improving the conductivity.[23, 24]
Inwet-chemicalrouteacetate has been used tosynthesis all materials. Acetates are large molecules which
could prevent the displacement of iron ion (Fe3+) withTi4+. This is also resulting in low values of EDSfor
BTF 33% (WCR). Another factor is that iron is a 3+ charged ion (in the starting material) which is a
“hard-ion” this will lead to a lower polarization. The high polarization of an ion will lead to an easier
transport of the ion into the structure. The indium ion In3+ is a “soft-ion” with a high polarization factor,
that’s why it’s easy for indium ions to travel through the structure and exchanges with Ti4+ ions. The
main factorwhich is blocking the iron ions to integrate into BaTiO3 is because it’s a hard metal, meaning
that electrons are close to the nucleus. These factors are leading to a repulsion effect within BaTiO3
structure. The key to improve the interaction of iron ions with BaTiO3 is to use small molecules to avoid
the blockage of substitution. Differentstarting materials like chlorides or nitrites can be used to improve
the transport of the hard-ions into the structure.
6 Conclusions
BaMxTi(1-x)O(3-δ) (M=In and Fe; x=0,17 and 0,33) were prepared viasolid state reactionand wetchemical
route and the materials have been characterized with different techniques. The thermogravimetric
analysis results have shown that all as-prepared and hydrated samples did show significant hydration
level between 68-93% of the maximum theoretical hydration level. By increasing the ratio of doping in
iron doped material, the microstructure was resulting in a denser structure. While for indium doped
materials, the density was decreased. The highest density was successfully achieved by wet-chemical
route, which yielded a relative density of 98,6% for BaIn0,17Ti0,83O(3- δ). This method did also increase
slightly the density for iron doped material (86,5%) compared to the solid-state route. It was foundthat
the iron doped samples are adapting a hexagonal perovskite structure and indium doped samples are
adapting a cubic perovskite structure. The FT-IR confirms the presence of 𝑂 − 𝐻 band in all hydrated
samples compared to the vacuum dried ones. Slightly higher conductivity has been measured under

43
humid condition proportional withtemperature compared tothe dry condition.The cubic structure (BTI
33 SSR) is promoting the conductivity slightly (comparedtoBTF33 (WCR), whichindicatesthat the main
charge carriers are protons. The hexagonal phase has shown lower proton conductivity by order of half
magnitude compared to BTF 17 (SSR). The conductivity has also increased in humid synthetic air than
nitrogen for the whole temperature range (150-850°C) for all samples, which is significant for p-type
semiconductor materials under oxidizing atmosphere. The highest conductivity at 400°C was shown in
BTI 33 (SSR) 𝜎 = 1,79 × 10−3 𝑆𝑐𝑚−1 and for BTF 17 (SSR) 𝜎 = 2,00 × 10−3 𝑆𝑐𝑚−1, indicating that the
hexagonal structure is not promoting the conductivity.The results indicate that the proton conductivity
of BaFexTi(1-x)O(3-δ), BaInxTi(1-x)O(3- δ) for the wet condition has higher magnitude versus the dry
atmosphere. The total conductivity whichisthe sum of bulk and grain conductivity,is showing a mixture
of ionic and electronic conductivity and this is known as cathode properties (both BTF 17% and 33%).
Indium 33% doped BaTiO3 is showing a typicalproton conductivity whichis resulted as “plateau effect”
in the complex graph.
7 Future work
The promising results that have been shown for wet chemical route i.e. high density should be
investigated and optimized further. Since the obtained results were not extracted form same synthesis
route a general as well adetailed description is not possible between the twosynthesis routes. Therefore,
future workwill be focusing on resynthesizing all impure samples with both routes in order to study the
conductivity as well microstructure (grain size and boundary). Scandium doped BaTiO3 synthesised
through solid state route needs more heat treatment and previous XRD diffractogramis showing almost
pure perovskite phase and also starting same material synthesising through wet chemicalroute. There is
a large interest in the structure, oxygen vacancies and the atom ordering therefore neutron diffraction
data need to be collected and studied for all samples. After comparing the solid-state route and wet
chemical route, another sintering technique will be used, which is hydrothermal method. The Rietveld
refinement for indium 33% doped BaTiO3 has shown lower cell parameter compared to 17% which is
needed to be investigated and understand the cause behind this reduction.

44
8 Appendix A: XRD Figures
This appendix is for results that have not been characterized with other techniques (SEM, TGA, rietveld
refinement and impedance spectroscopy) and for samples that have shown some impurity level (not
100% pure).
8.1 X-ray diffraction
Figur 1: XRD diffractofram with different temperature sintering for BTF 17 wet.
400°C/2h
800°C/10h
1350°C/30h

45
Figur 2: XRD diffractofram with different temperature sintering for BTF 33 SSR.
Figur 3:XRD diffractofram with different temperature sintering for BTI 17 SSR.
1250°C/18h_750°C/6h
1250°C/18h_750°C/6h
1250°C/24h_750°C/6h
1250°C/24h_750°C/6h
1350°C/27h
1350°C/24h
1350°C/24h
1200°C/24h
1000°C/24h
1350°C/24h

46
Figur 4: XRD diffractofram with different temperature sintering for BTI 33 (WCR).
Figur 5:XRD diffractofram with different temperature sintering for BTS 17 SSR. Sintering temperature 1000°C 12h –
1405°C 14h
1350°C/30h
800°C/10h
400°C/2h
VC950°C/35h+1350°C/30h

47
9 Appendix B: Calculations
9.1 Relative density
The relative density is calculated though a ratio between the measured density and the theoretical
density as following:
𝜌 𝑝𝑒𝑙𝑙𝑒𝑡 =
𝑚 𝑝𝑒𝑙𝑙𝑒𝑡
𝑉 𝑝𝑒𝑙𝑙𝑒𝑡
𝑉 𝑝𝑒𝑙𝑙𝑒𝑡 = 𝜋𝑟2ℎ
Where r forBTI17(WCR) is the radius and h is the thickness of the pellet, here is example forcalculation:
𝑉 𝑝𝑒𝑙𝑙𝑒𝑡 = 𝜋𝑟2ℎ = 𝜋 × (2,7375)2 × 2,22 = 52,2650 𝑚𝑚3 = 0,052265 c𝑚3
𝜌 𝑝𝑒𝑙𝑙𝑒𝑡 =
𝑚 𝑝𝑒𝑙𝑙𝑒𝑡
𝑉 𝑝𝑒𝑙𝑙𝑒𝑡
=
0,3136𝑔
0,052265cm3 = 6,0
𝑔
𝑐𝑚3
𝜌 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 =
𝜌 𝑝𝑒𝑙𝑙𝑒𝑡
𝜌 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙
=
𝑝𝑒𝑙𝑙𝑒𝑡 𝑑𝑒𝑛𝑖𝑠𝑡𝑦
𝐶𝑟𝑦𝑠𝑡𝑎𝑙 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
Figur 6:XRD diffractofram with different temperature sintering for BTS 33 SSR. Sintering temperature 1000°C 12h -
1455°C 15h.

48
Sample 𝜌 𝑝𝑒𝑙𝑙𝑒𝑡 𝜌 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝜌 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒
BTF 17 4,581 6.05888 75,61%
BTF 33 5,12 5.91691 86,53%
BTI 17 6,00 6.08600 98,59%
BTI 33 4,92 6.07337 81,01%
9.2 The hydration percentage
The degree of the hydration forthe hydrated sample is a ration between the recorded mass-loss and the
maximum theoretical mass-loss that would be observed for fully hydrated sample. During the heat-
treatment it’s assumed that only water is leaving fromthe structure. So the calculationof the percentage
of the hydration starts by calculating the ration (Rmin) of molar mass between vacuum dried sample and
fully hydrated sample, shows the minimal residual mass.
𝑅 𝑚𝑖 𝑛 =
𝑀 (𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒)
𝑀 (ℎ𝑦𝑑𝑟. 𝑠𝑎𝑚𝑝𝑙𝑒)
=
233,2849 𝑔/𝑚𝑜𝑙
234,7262 𝑔/𝑚𝑜𝑙
= 0,99386 = 99,386%
During the TG-analysis, if the sample display (99,386%) it will go fromfully hydrated to partial hydrated
(as-prepared sample), sinceits quite easy forsample toabsorb waterforatmosphere. If theresidual mass
ratio displays a higher value than 99,386%, it’s an indication of a sample with less hydration level.
Secondly, the possible maximum mass loss for fully hydrated could be calculated as following equation:
∆𝑚 𝑚𝑎𝑥 = 1 − 𝑅 𝑚𝑖𝑛 = 1 − 0,99386 = 0,00614 = 0,614%
The final calculationof the hydration degree (H) real mass loss of the sample whichis compared withthe
theoretical mass loss by following equation:
𝐻 =
∆𝑚 𝑠𝑎𝑚𝑝𝑙𝑒
∆𝑚 𝑚𝑎𝑥
=
∆𝑚 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙
∆𝑚 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙
=
0,57
0,614
= 0,92834 = 92,834%
Sample M (dry sample) M (hyd. sample) Rmin ∆𝑚 𝑚𝑎𝑥=1- Rmin H
BTF 17 233,2849g/mol 234,7262g/mol 99,386 % 0,614% 92,834%
BTF 33 233,1201g/mol 236,1828 g/mol 98,762 % 1,297% 76,29%
BTI 17 243,31 g/mol 244,751 g/mol 99,411 % 0,589% 91,718%
BTI 33 252,580 g/mol 255,643 g/mol 98,802 % 1,198% 68,445%

49
9.3 The total conductivity and activation energy
calculation (impedance data)
After refining all impedance data for each point, the data was saved in excel to simplify the calculationof
the total resistance (usually two different resistance is obtained as R1 and R2). The total conductivity 𝜎
was calculated through following equation:
𝜎𝑡𝑜𝑡𝑎𝑙 =
𝑇
𝐴 × 𝑅 𝑡𝑜𝑡𝑎𝑙
Where T is the thickness of the pellet, A is the average area of the electrodes of both side A and B of the
pellet and Rtotal is the totalresistance foreach temperature. After calculatingall𝜎𝑡𝑜𝑡𝑎𝑙, thedata was plotted
as log (𝜎𝑡𝑜𝑡𝑎𝑙)for each temperature against invers temperature (Arrhenius plot).
The activation energy was calculated by following equation:
𝜎 =
𝜎0
𝑇
exp (
−𝐸 𝑎
𝑘 𝐵 𝑇
)
Where 𝜎0is thepre-exponential factor,Tis the temperature, kB is Boltzmann constant and Ea is activation
energy. By plotting 𝑙𝑜𝑔(𝜎𝑇)against 1/T, straight line will be achieved if not the data need to be refined
again. The y-intercept of ln(𝜎0) and the slope correspond to(
−𝐸 𝑎
𝑘 𝐵 𝑇
). Therefore, activationenergy could be
calculated by fitting the observed data and extracting the slope of straight linear functions and
multiplying it with 𝑘 𝐵 constant.
The SI unit for conductivity is Siemens per meter (S/m) or per cm (S/cm), which is unit change as
following:
𝑆 = 𝛺−1
𝜎 =
1
𝑅
× 𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
𝐴𝑟𝑒𝑎
=
1
𝛺
× 𝑐𝑚
𝑐𝑚2 =
1
𝛺
𝑐𝑚
=
1
𝛺
×
1
𝑐𝑚
=
1
𝛺𝑐𝑚
=
𝑆
𝑐𝑚
= 𝑆𝑐𝑚−1
10 Acknowledgment
I would like to express my gratitude to my supervisor Dr Seikh M.H. Rahman & Dr Zareen Abbas forthe
useful comments, remarks and engagement through the learning process of this bachelor thesis and
another special thanks to Prof.Elisabet Ahlberg. Furthermore, I wouldlike to thank Prof.Sten Ericsson
for introducing me to the Solid state 21 conferenceas well forthe support as well the funds to present a
nice poster. Also, I like to thank Dr. Dariusz WojciechWardecki,Nico Torino, Xuncheng Shi and Laura
Mazzei, whohave willingly shared their precious time during the process. I wouldlike to thank my
loved ones, family as wellfriends whohave supported me throughout entire process, both by keeping
me harmonious and helping me putting pieces together.

50
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