chapter - ii experimental techniques 2.1....
TRANSCRIPT
CHAPTER - II
EXPERIMENTAL TECHNIQUES
2.1. Introduction
2.2. Preparation methods
2.2.1. Sol-gel process
2.2.1.1. Colloidal process
2.2.1.2. Chemical polymerization process
2.2.1.3. Advantages of the Sol gel process
2.2.2. Hydrothermal process
2.2.2.1. Advantages of Hydrothermal process
2.2.2.2. Disadvantages of Hydrothermal process
2.2.3. Co-precipitation process
2.2.3.1. Advantages of Co-precipitation process
2.2.3.2. Disadvantages of Co-precipitation process
2.2.4. Polyol process
2.2.4.1. Advantages of Polyol process
2.2.4.2. Disadvantages of Polyol process
2.2.5. Combustion Process
2.2.5.1. Combustion of Fuel – Oxidant
2.2.5.2. Polymeric Precursors process
2.2.5.3. Pechini Process
2.2.5.4. Advantages of Combustion process
2.2.5.5. Disadvantages of Combustion process
2.3. Preparation methods of polymer solid electrolytes
2.3.1. Solution-casting process
2.4. Characterization techniques
2.4.1. X-Ray Diffraction (XRD)
2.4.2. Fourier transforms infrared spectroscopy (FTIR).
2.4.3. Scanning Electron Microscopy (SEM)
2.4.4. Thermal Analysis
2.5. Principles of Impedance spectroscopy
2.5.1. Basic theory
2.5.2. Series combination of R and C
2.5.3. Parallel combination of R and C
2.5.4. Preparation of pellets for impedance measurement
References
CHAPTER - II
EXPERIMENTAL TECHNIQUES
2.1. Introduction
In recent times, a number of new lithium ion based polycrystalline,
polymer materials with high ionic conductivity have been synthesized and find
potential applications in various solid state ionic devices [1-10]. Recently,
further, enhancement of the electrical conductivity and mechanical properties
have been achieved by dispersing nanosized metal oxides in the polymer
solid electrolytes for better ionic device applications including lithium batteries.
This chapter briefly describes about the synthesis of rare earth based
lithium silicates by sol-gel process, nanocrystalline metal oxides by
combustion process and lithium ion conducting polymer solid electrolytes by
solution casting method and their characterization by different experimental
techniques like XRD, FTIR, TG/DTA, SEM-EDX and impedance.
2.2. Preparation methods
2.2.1. Sol-gel process
In recent years, the sol-gel method has become one of the most
popular and important techniques to synthesize various types of tailor made
new materials, including high ionic conductors with high homogeneity and
purity [11]. The versatility of the sol gel method is due to mixing of starting
chemicals (precursors) in the solution form at much lower temperature which
gives good control of various components at atomic level.[12] This technique
21
has been extensively used to prepare different types of new materials in the
bulk, powders, sheets, fibers, thin films, etc., for various advanced
technological applications. Thus, the sol gel route is more suitable for the
synthesis of glassy / amorphous and crystalline materials than conventional
methods. There are two essentially different routes in the sol gel process to
produce the various types
1. Colloidal process
2. Chemical polymerization process
2.2.1.1. Colloidal process
This process involves the dispersion of colloidal particles in a liquid to
form a sol and then destabilization of the sol to form a gel. This process is
represented in fig 2.1.a. In colloidal process, the aqueous solution of silicic
acid is used as the source of SiO2 network and also to form the sol. The
polymerization of monomer silicic acid leads to the formation of branched
chains in three dimensions, which result the gel and can be converted into
amorphous solids by one of the following ways.
Heat-treatment of the gel below the glass transition temperature
(Tg) to obtain glass through the polymerization.
Calcining the gel well above the Tg but within the melting point
range to form the polycrystalline sample.
22
(a) (b)
Fig.2.1. a and b. Flow chart representation for the preparation of SiO2 monolithic gel by sol-gel process a) colloidal route and b) chemical polymerization route.
Colloidal route
Metal salt SiCl4
Ultra pure particles
SiO2 Sol
Sio2 gel
Monolithic
pH adjustment
Chemical polymerization route
Organo metallic Si(OR)4
Acid catalyst
Polysilonane sol
Solid gel
Monolithic
pH adjustment
Hydrolysis and Polymerization
23
2.2.1.2. Chemical polymerization process
Alkoxide (like TEOS for preparing SiO2) is hydrolyzed with water in the
presence of corresponding alcohol to form the sol. Then the sol is casted to
form the gel and it heated to obtain the monolithic SiO2. The synthesis
procedure of SiO2 glass by chemical polymerization is shown in fig 2.1 (b) and
various steps involved in the sol gel process are briefly discussed.
The seven steps involved in the sol gel process are as follows
a. Mixing
The alkoxide precursor [Si(OR)4 (R=CH3, C2H5, C3H7 etc) is hydrolyzed
by mixing with water. The corresponding reaction mechanisms are as
follows.
Si OR
OR
OR
RO Si OH
OH
OH
HO4H2O 4ROH
Si OR
OR
OR
RO Si OH
OR
OR
ROH2O ROH
24
The hydrolyzed silica molecules can link together in the condensation
reaction by the removal of H2O and R-OH. This type of the reaction can
continue to build a larger and larger by the process of polymerization.
b. Casting
The prepared sol can be cast into mould to obtain the required shape.
The mould must be selected to avoid adhesion of the gel.
c. Gelation
As mentioned in the step I, with time, the condensation reaction can
build up larger and larger network by the process of polymerization to form
three-dimensional network, which leads to form the gel. The gelation time will
depend up on the temperature, solvent, pH condition and also removal of the
solvent.
d. Aging
Aging is the step maintaining the casted object for a period of time.
During the aging, the polycondensation continues and resulting the expulsion
of liquid from the pores. These increase the thickness of particle necks and
decrease the porosity. Thus, with aging, the strength of the gel increases.
Si OR
OR
OR
RO Si OR
OR
OR
HO Si O
OR
OR
RO Si
OR
OR
OR
ROH
25
e. Drying
Liquid existing in the interconnected pore network is removed during
the drying process. Thus, there is a decrease in the volume of the gel, which
is equal to the volume of the liquid lost by evaporation. Here after drying, the
pores of the gel substantially emptied.
f. Dehydration or chemical stabilization
The removal of the unwanted elements likes H and R respectively from
Si-OH (silanol) and Si-OR bonds to obtain the chemically stabile required
compound.
g. Densification
Densification is the last treatment process of gel. By heating the
porous gel at high temperatures, the pores can be eliminated and densified
poly crystalline can be obtained equivalent to the fused quartz or fused silica.
The densification temperature depends on the dimension of the pore network,
the conductivity of pores, surface area etc.
2.2.1.3. Advantages of the Sol gel process
1. Better homogeneity and purity
2. Low temperature preparation saving energy.
3. Minimize the evaporation losses.
4. Minimize air pollution.
5. No reaction with container.
26
6. Bypass phase separation.
7. New non-crystalline solids outside the range of normal glass
formation.
8. Better glass products from the special properties of the gel.
9. Special properties (e.g. fibers and films).
Hence, in the present investigation, lithium samarium silicate
(LiSmSiO4), Lithium lanthanum silicate (LiLaSiO4) and lithium dysprosium
silicate (LiDySiO4) are taken to synthesize by tailor made sol-gel process. The
synthesis procedures of the rare earth based lithiumsilicate by sol-gel process
are discussed in more detail in the chapter III.
2.2.2. Hydrothermal process
Water is an excellent solvent for many ionic compounds. It can even
dissolve non-ionic covalent compounds under high pressure and high
temperature. In hydrothermal synthesis, the above property of water has been
effectively exploited for the preparation of fine powders of metal oxides [13-
15]. Under these hydrothermal conditions, water plays two roles: 1) as
pressure transmitting medium and 2) as a solvent for reacting solids. Such
hydrothermal conditions effectively brings down the activation energy for the
formation of final phase, which can also speed up the reaction between the
solids which otherwise would occur only at very high temperatures [16-17]. An
autoclave is invariably employed to achieve hydrothermal conditions. The
pressures attained are in the range of 10 to 150 kilobar which depends on the
chosen temperature of water (>373 K). Powders are either crystalline or
27
amorphous depending on chosen hydrothermal temperature [18-22]. This
hydrothermal has certain advantages as well as some disadvantages, which
are listed below:
2.2.2.1. Advantages of Hydrothermal process
1. Powders are formed directly from the solution.
2. It is possible to control particle size and shapes by using
different starting materials and hydrothermal conditions.
3. Resulting powders are highly reactive which aid in low
temperature sintering.
2.2.2.2. Disadvantages of Hydrothermal process
1. Prior knowledge on solubility of starting materials is required.
2. Hydrothermal slurries are potentially corrosive.
3. Accidental explosion of the high pressure vessel cannot be ruled
out.
2.2.3. Co-precipitation process
In this method, the required metal cations from a common medium are
co-precipitated usually as hydroxides, carbonates, oxalates, formates or
citrates [23-25]. These precipitates are subsequently calcined at appropriate
temperatures to yield the final powder. For achieving high homogeneity, the
solubility products of the precipitate of metal cations must be closer [26]. Co-
precipitation results in atomic scale mixing and hence the calcining
28
temperature required for the formation of final product is low. This leads to
lower particle size in the resulting multi component oxide powders [27].
However, each synthesis requires its own special conditions, precursor
reactions, etc. Also, co precipitation route required to control the
concentration of the solution, pH, temperature, and stirring speed of the
mixture in order to obtain the final product with required properties [28-29].
2.2.3.1. Advantages of Co-precipitation process
1. Homogeneous mixing of the reactant precipitates reduces the
reaction temperature.
2. Simple direct route for the synthesis of fine metal oxide
powders, which are highly reactive in low temperature sintering.
2.2.3.2. Disadvantages of Co-precipitation process
1. This process is not suitable for the preparation of high purity,
accurate stoichiometric phase.
2. This method does not work well, if the reactants have very
different solubility as well as different precipitate rate.
3. It is not having universal experimental condition for the
synthesis of various types of metal oxides.
2.2.4. Polyol process
Ethylene glycol has been widely used in the polyol process for the
synthesis of metal (both pure and alloyed) nanoparticles due to its strong
29
reducing power and relatively high boiling point (~197 oC). Recently, it has
been widely used for the synthesis of nanocrystalline ceramic powders that
involved, complexation with ethylene glycol, followed by polymerization [30-
33]. In addition, ethylene glycol has been used to fabricate meso structures of
titania, tin dioxide, zirconia, and niobium oxide by forming glycolate
precursors because of its coordination ability with transition metal ions. This
route involves hydrolysis and inorganic polymerization carried out on the salts
dissolved in a polyol medium. The polyol acts as a solvent for the precursor
salts because of its high relative permittivity, and allows one to carry out
hydrolysis reactions under atmospheric pressure in a large temperature range
up to the boiling point of the polyol [34-35].
2.2.4.1. Advantages of Polyol process
1. Low temperature process which can able to control the
properties of the particles such as size, shape and uniformity,
etc.
2. It yields high pure organic free powders.
2.2.4.2. Disadvantages of Polyol process
1. Large amount of poly hydroxyl alcohol requirement.
2. Phase separation while synthesizing the multi-component
oxides.
3. Choosing the suitable poly hydroxyl alcohol for individual
processes.
30
4. Collecting and purifying the intermediate particles are
complicated.
2.2.5. Combustion Process
Combustion is a complex sequence of chemical reactions between a
fuel and an oxidant accompanied by the production of heat or both heat and
light in the form of either a glow or flames. The combustion concept that using
the art of rapid thermal degradation of precursor chemicals reaction with
oxygen has been effectively used for the synthesis of variety of metal oxides
in nanoscale. [36-40] Based on the fuels and their combinations with the
metal ions sources (commonly metal nitrates, acetates, hydroxides),
combustion process has classified into the following categories [41-42].
2.2.5.1. Combustion of Fuel – Oxidant
Fuel-oxidant combustion technique involves an exothermic
decomposition of a fuel – oxidant precursors such as urea- nitrate, glycine-
nitrate, DHF- nitrate, etc, relatively at lower temperatures [43-45]. Also, it
explores highly fast and self sustaining exothermic reaction between the
metal salts and organic fuels. The heat required for the phase formation is
supplied by the reaction itself and not by an external source. During this
ignition process, large volume of gases will evolve which prevent the
agglomeration and lead to the formation of fine powders with nano structures.
The release of heat during the combustion reaction depends on the fuel –
oxidant stoichiometry in the precursor composition. The fuel – oxidant
stoichiometry is used to calculate the required fuel, based on the thermo
31
dynamical concepts used in the field of propellants and explosives, for the
required nature of combustion process [46].
2.2.5.2. Polymeric Precursors process
The polymeric precursor route is known to be simple cost effective and
versatile low temperature combustion route for the synthesis of multi
component metal oxides relatively lower temperatures [47]. The general idea
of this process is to distribute the metal ions atomistically through the
polymeric structure and to inhibit their segregation and precipitation from the
solution [48]. Further heating of these polymeric intermediates at appropriate
temperatures, yields ultra fine nanocrystalline metal oxides. Generally
hydroxyl carboxylic acids such as citric acid, tartaric acid, etc., are used as a
polymerizing as well as chelating agents in this process [49]. The
physiochemical properties of the synthesized powders are critically depend on
the properties of polymeric intermediates, which influence on the combustion
parameters such as ignition temperature, heat evolution, combustion duration
etc [50]. Hence, wide ranges of polymeric precursors have been investigated
in order to control the structural properties of final products.
2.2.5.3. Pechini Process
Pechini process also one of the combustion process, is based on the
ability of certain weak acids (citric acid, tartaric acid, polyacrylic acid, etc.) to
chelates the various metal ions. These metal carboxylates can undergo
polyesterification when heated with polyhydroxyl alcohol (ethylene glycol,
glycerol, polyvinyl alcohol, etc.,) and lead to the formation of polymeric resin,
with three dimensional networks [31, 50-51]. The cations are uniformly
32
distributed throughout polymeric resin, which inhibits the precipitation.
Further, the calcinations of dried resin yield ultra fine oxide powders at very
low temperature.
2.2.5.4. Advantages of Combustion process
Gel combustion methods show advantages over the earlier mentioned
processes mainly due to the following important facts,
1. Low cost and low temperature process (compared to alkoxide
based sol gel methods).
2. Better control of stoichiometry.
3. Crystalline size of the final oxide products, produced by these
methods is invariably in the nanometer range.
4. Exothermic reaction makes product almost instantaneously.
5. Possibility of multicomponent oxides with single phase and high
surface area.
2.2.5.5. Disadvantages of Combustion process
1. Contamination due to carbonaceous residue, particle
agglomeration, no control on particle morphology.
2. Understanding of combustion behavior is needed to perform the
controlled combustion in order to get final products with desired
properties.
33
3. Possibility of violent combustion reaction, which needs special
production.
In the present investigation three different types of combustion
processes are employed for the synthesis of nanocrystalline metal oxides
TiO2, Dy2O3 and MgO. The details of the synthesis processes are discussed
in chapter IV.
2.3. Preparation methods of polymer solid electrolytes
The different methods are used to prepare various polymer solid
electrolytes. The various preparation methods are given below.
1. Solution-casting method
2. Thermal evaporation method
3. Flash evaporation method
4. Hot pressing method
5. Pyrolysis
6. Film blowing
7. Polymerization of monomer
8. Gaseous discharge
9. Sputtering
In the present investigation, the solution casting method is used to
prepare three different types of nano composite polymer solid electrolyte,
which is briefly discussed.
34
2.3.1. Solution-casting method
Polymer solid electrolyte films are generally obtained by solution
casting method. The required polymer and the inorganic salts are dissolved
in suitable solvents (e.g. THF, Acetonitrile, methanol, ethanol, acetone,
deionized water, etc.) and stirred & heat treated continuously till to get the
homogeneous viscous solution. The viscous solution casted on the glassy
substrates. It allows the solvent to evaporate and form the polymer solid
electrolyte film. The schematic representation of the preparation procedure of
polymer solid electrolyte film is shown in fig 2.2.
In the present investigation, three nanocrystalline metal oxides (TiO2,
Dy2O3 and MgO) are dispersed in three different polymer solid electrolytes
(PVdF-Li+, PVdF/PMMA - Li+, PVdF-HPF - Li+) and prepared three different
nanocomposite polymer solid electrolytes (PVdF-Li+ - (TiO2, Dy2O3 and MgO),
PVdF/PMMA - Li+ (TiO2, Dy2O3 and MgO), PVdF-HPF - Li+ (TiO2, Dy2O3 and
MgO)) using solution casting method. The detailed preparation procedures
for the three different nanocomposite polymer solid electrolytes using solution
casting method are discussed in Chapter V.
35
Fig 2.2. Flow chart representation for the preparation of nanocomposite polymer solid electrolyte (NCPSE) film using solution casting method.
Polymer dissolved in solvent
LiCl4 dissolved in solvent
Metal Oxide dispersed in solvent
Continuous stirred at 333K
EC:DMC (1:1)
Under the sonication
Casted on the glassy substratee
NCPSE film
36
2.4. Characterization techniques
2.4.1. X-Ray Diffraction (XRD)
X-ray diffraction method is one of the most important
characterization tool used in solid state chemistry and material science for
studying the atomic and molecular structure of crystalline substances.
Physical properties of the solids are in some way dependent on their crystal
structure and phase.
X-Ray Diffraction (XRD) measurements were carried out for all the
prepared samples using X-ray powder diffractometers (PHILIPHS make
X’Pert PRO PANalytical and Rigaku miniflex, Japan) with Cu-Kα radiation of
wavelength (λ) 1.5418 Å, with a scan rate of two degree per minute from 10 –
80o and also with an accelerating voltage of 40 kV and current 30 mA. Ni filter
was used to minimize CuKβ radiation. XRD patterns were recorded for all the
prepared powders and polymer samples. The crystalline phase identification
were compared with the JCPDS data
Crystallite size can be estimated from XRD patterns using the
Scherrer equation as follows. [52-55]
LB
0 9
12
.cos
Where, = Wavelength of the radiation used in
B= Bragg`s angle in degrees
1/2 = Full width at half maxima (FWHM) in radians
37
1/2 is calculated using the following expression:
2/122
2/1 )( SM
Where
M = measured width of the line of sample and
S = measured width of the Si standard.
Peak corresponds to the (111) plane of the Si standard was used to
derive the instrumental broadening. NBS silicon standard of known crystallite
size was used as external standard for estimation of the instrumental
broadening.
2.4.2. Fourier transform infrared (FTIR) spectroscopy
Each prepared sample (solid substance) is ground with potassium
bromide (KBr) (1:20) and made into thin transparent pellets using the micro
pelletizer. Also very thin transparent KBr pellet, as a reference, is made using
micro pelletizer. Fourier Transform Infrared (FTIR) Spectra are recorded for
all prepared thin transparent pellet samples using Schimadzu FTIR –
8300/8700 spectro photometer, 4 cm-1 resolution, auto gain, between the
frequency range of 4000 – 400 cm-1 for 32 scans. Schematic diagram,
showing the optical path in a FTIR spectrometer is shown in fig 2.3.
38
Fig. 2.3. Schematic diagramspectrometer.
2.4.3. Scanning Electron Microscopy
Small amount of each prepared
sonicated in few minutes. The dispersed sol was dropped on the conducting
carbon tape pasted over the aluminium stub. Further, thin layer of gold was
coated on each sample using the sputter coater for better conduction.
Microstructure of the each sample was recorded in the form of SEM images at
different magnification using scanning
3400N, Japan.
Photograph of the SEM
the present investigation is sh
Schematic diagram, showing the optical path in a FTIR
Scanning Electron Microscopy
amount of each prepared sample is dispersed in acetone and
sonicated in few minutes. The dispersed sol was dropped on the conducting
carbon tape pasted over the aluminium stub. Further, thin layer of gold was
coated on each sample using the sputter coater for better conduction.
Microstructure of the each sample was recorded in the form of SEM images at
different magnification using scanning electron microscopy,
Photograph of the SEM – setup (HITACHI S-3400N, Japan) used in
the present investigation is shown in fig 2.4.
showing the optical path in a FTIR
sample is dispersed in acetone and
sonicated in few minutes. The dispersed sol was dropped on the conducting
carbon tape pasted over the aluminium stub. Further, thin layer of gold was
coated on each sample using the sputter coater for better conduction.
Microstructure of the each sample was recorded in the form of SEM images at
opy, HITACHI S-
3400N, Japan) used in
39
Fig 2.4 Photograph of the SEM – setup (HITACHI S-3400N, Japan)
2.4.4. Thermal Analysis
TG/DTA curves are recorded for all the prepared dried gel samples
using TA instruments SDT Q600 V20.5 at the heating rate of 10 oC/min
between 30 - 900 oC under nitrogen atmosphere. Also DSC curves were
recorded for all the prepared polymer samples using TA instruments SDT
Q6000 at the heating rate of 10 oC/min between 30 - 250 oC under nitrogen
atmosphere
2.5. Principles of Impedance spectroscopy
Impedance is the opposition to flow of current, which is given by the
ratio of the applied voltage to the resultant current. Impedance spectroscopy
is a powerful technique used for electrical characterization of an electrolyte
material. It is a perturbation technique, which involves the measurement of
the current through a solid electrolyte when a sinusoidal voltage of low
amplitude is applied. This analysis has been widely used to investigate the
40
elementary process such as bulk conduction, grain boundary conduction, and
electrode-electrolyte interface process in the relevant frequency domain.
Study of conductivity as a function of parameters such as temperature,
chemical potential of the conducting species and sample dimension can yield
the activation energy and relaxation frequency for various conduction modes,
dielectric constant, diffusion coefficient, phase transition and microstructure
correlation [56].
2.5.1. Basic theory
A small amplitude of ac signal is used in impedance measurement to
perturb the system.
The applied potential E() is given by,
ܧ = (ݐ) expܧ
(2πf) is the angular frequency, t is time. The output current of the
system is also a sinusoidal and represented by,
ܫ = ݐ) expܫ + )
According to the Ohm’s law, impedance of the circuit (Z) at any angular
frequency can be represented by,
Z = E/I = ( Eo / Io )exp (-j)
= Zo exp (-j)
41
= Z cos - jZ sin
Z = Zr - jZi
Where j is the imaginary number having the value of -1, Zr and ZI are
respectively real and imaginary parts of the impedance. The phase angle is
represented by
= tan-1(ZI /Zr)
For pure resistor (R), capacitor (C) and inductor (L) impedance is given
by the following representations:
Z = R + 0 j
Z = 0 – j / C
Z = 0 + j L
From the above equations, it is seen that the impedance due to
capacitor and an inductor depend on the frequency of the input signal. The
plot of real and imaginary parts of impedance for a particular range of
frequency is known as impedance spectrum and it appears as semi circles or
straight lines depending on the combinations of resistance and capacitance. If
resistance and capacitance are connected in series or parallel, the impedance
of the circuits is given as follows.
2.5.2. Series combination of R and C
A circuit containing a resistance and a capacitance in series is shown
in fig 2.5.a. The total impedance (Z) of the circuit is given by
42
Z = R + ( 1 / j C) = R- (j / C)
The above equation contains real (Z’) and imaginary (Z”) terms as
indicated below:
Z’ = R and
Z” = 1/C
Fig 2.5. a also shows the complex impedance plot (Z” vs Z’) for the
circuit containing a resistance and a capacitance in series. From the Fig 2.5.
a, the complex impedance plot gives a vertical spike, because Z’ is of fixed
value and Z” decreases with increasing . The point at which the vertical
spike is touch in the real axis gives the resistance value of the circuit as
shown in fig.2.5.a
Fig. 2.5. a & b. Impedance plot for the series and parallel combinations of R and C.
2.5.3. Parallel combination of R and C
A circuit containing a resistance and a capacitance in parallel is shown
in fig 2.5.b. The total impedance (Z) is given by,
43
Z = (1 / R + jC)-1
= R/ (1 + jRC)
= {R / (1 + (RC)2)} – {RjRC / (1+(RC)2)}
Therefore,
Z` = R / (1 + (RC)2) and Z`` = RRC / (1+(RC)2)
Fig 2.5. b also shows the complex impedance plot (Z” vs Z’) for the
circuit containing a resistance and a capacitance in parallel. From Fig 2.5. b,
the complex impedance plot gives a semicircle. The point at which the
semicircle is touch in the real axis gives the resistance value of the circuit as
shown in fig.2.5.b
2.5.4. Preparation of pellets for impedance measurement
All the three prepared LiSmSiO4, LiLaSiO4 and LiDySiO4 samples were
grounded to fine powders with isopropanol as a binding solvent and made into
pellets using the pelletizer under a static pressure of 5 tons to form the pellet
of dimension 10 mm diameter and 2-3 mm thickness. All the three prepared
pellet samples were coated with silver paste as electrodes.
The prepared three nanocrystalline metal oxide samples were
grounded to fine powder and made into pellet using the pelletizer under a
static pressure of 8 tons to form the pellet dimension of 10mm diameter and
2-3mm thickness.All the prepared pellets were coated with silver paste as
electrodes.
44
The final pellet is of the following form for impedance measurements.
Silver electrode/metal oxide sample pellet/silver electrode
The real (Z) and imaginary (Z) parts of the impedance data were
measured on the pellets of metal oxide samples using a Nova control high
performance frequency analyzer in the frequency range 100mHz to 1MHz at
different temperatures. Bulk conductivity of the metal oxide samples were
calculated from the analyzed impedance data obtained at different
temperatures using the nova control winfit software.
45
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