sample preparation and characterization -...

Chapter - 4

Sample preparation

and

Characterization

This chapter essentially discusses synthesis methods; the

Sol-gel auto combustion technique, in situ polymerization

method and the procedures followed to prepare pure and their

composites of every series in the present work. List of analytical

techniques used and the parameter obtained from each

technique are also covered.

Sample preparation and characterization Chapter - 4

- 87 - Ph.D. Dissertation

4.1 Sol-gel auto combustion technique

In present work, all the samples were prepared by using Sol-gel auto

combustion technique. In Sol-gel auto combustion technique, oxidizing metal salts

and combustion agent (fuel) are essential for the combustion process. Metal nitrates

and citric acid were used as oxidizing salts and combustion fuel for all the sample

preparations. All chemicals were of high purity Analytical reagent and used without

further purification. The Sol-gel auto combustion technique has been proved to be

extremely facile, time-saving and energy-efficient route for the synthesis of ultra fine

hexaferrite powders.

Principle:

The Sol-gel method is based on gelling and subsequent combustion of an

aqueous solution containing salts and organic fuel, giving a voluminous and fluffy

product with large surface area. Oxidizing metal salts, such as metal nitrates, and a

combustion agent (fuel), such as citrate acid, polyacrylic acid or urea are used as

starting materials [1]. Due to the good capability of chelating metallic ions and to low

decomposition temperatures, citric acid is suited for obtaining precursors of transition

metal oxides. This method uses a solution during the initial step of the preparation

process, so the reactants are well-dispersed and in a much higher reactive state,

providing a homogeneous reaction mixture. The organic fuel plays an important role,

it is the fuel for the combustion reaction; which forms complexes with metal ions

preventing the precipitation of hydroxilated compounds [2]. The combustion can be

considered as a thermally induced redox reaction. The energy from the exothermic

reaction between oxidant and reductant can be high enough to form fine particles [3].

Typical Sol-gel process:

Metal nitrates, are dissolved in distilled water to prepare precursor solutions

with an ionic ratio in agreement with the target product. The stochiometric amount of

combustion agent (fuel) is added and ammonia is then used to adjust the pH to 7.

Solution is allowed to evaporate on a hot plate maintaining the solution temperature at

80-90 oC. As water evaporates, the solution will turn into a viscous gel. This gel

precursor is preheated for further dehydration which is followed by a sudden self-

combustion, resulting in the evolution of large amounts of gases and the formation of



fluffy foam. The combustion could be of the flame type or the smoldering type

depending on the combustion agent concentration [4]. The flames extinguish within a

few seconds, while the smoldering could last for several minutes. The type of

combustion plays an important role in controlling the particle size in the combustion

result.

Advantages of Sol-gel auto combustion process:

Sol-gel combustion methods show advantages over the other processes mainly

due to the following important facts,

Low cost and low temperature process.

Better control of stoichiometry.

Crystalline size of the final oxide products is invariably in the nanometer

range.

Exothermic reaction makes product almost instantaneously.

Possibility of multicomponent oxides with single phase and high surface area.

Limitations of Sol-gel auto combustion process:

Contamination due to carbonaceous residue, particle agglomeration, poor

control on particle morphology.

Understanding of combustion behavior is needed to perform the controlled

combustion in order to get final products with desired properties.

Possibility of violent combustion reaction, which needs special production.

4.2 Samples preparation

4.2.1 Synthesis of M-type hexaferrite (BaFe12O19) using Sol-gel auto

combustion technique

Barium nitrate Ba(NO3)2 (Merck, GR grade), Iron nitrate, Fe(NO3)3.9H2O

(Sigma Aldrich, > 98 % purity), Citric acid, C6H8O7 (Merck, GR grade) and 25 %

aqueous solution of NH4OH (Merck , GR grade) were used as starting materials.



Stoichiometric amounts of iron nitrates and barium nitrates were dissolved in a

minimum amount of double distilled water. Citric acid in the molar ratio 1:1 to total

moles of metal nitrates was dissolved in equal amount of double distilled water

separately.

Fig. 4.1. Schematic diagram for the preparation of BaFe12O19 hexaferrite powder

using Sol-gel combustion technique

Then the aqueous solution of citric acid was added drop by drop into the metal

nitrate solution. This mixed solution was constantly stirred on a hot plate at 45 oC for



the chelation of Ba2+

and Fe3+

ions in the solution. The clear brownish solution thus

obtained had a pH = 2. Aqueous ammonia (25% w/v) solution was then added drop

by drop under constant stirring in order to adjust the pH value to about 7. The dark

greenish solution was allowed to evaporate on a hot plate maintaining the solution

temperature at 80 oC. As a result of the increasing concentration, the viscosity raised

due to the crosslinking of carboxylato-metal complexes into a three dimensional

structure [5], with ionic metal carboxyl and ammonium-carboxyl bonds [6,7], and, on

further dehydratation, a gel started to form. Continuous heating led the boiling and the

swelling of the gel with evolution of a large amount of gases (CO2, H2O, N2) [8].

Combustion started in the hottest zones of the beaker and propagated from the bottom

to the top like the eruption of a volcano, the gel completely burnt out to form a loose

powder.

The general chemical reaction involves in synthetic process can be written as

Ba(NO3)2 + Fe(NO3)3.9H2O + C6H8O7 + NH3.H2O

BaFe12O19 + CO2 + N2 + H2O (4.1)

When the dried precursors are heated, the following reactions occur:

Dried precursors → γ-Fe2O3 + Ba2+

,

γ-Fe2O3 + Ba2+

→ BaFe2O4,

BaFe2O4+5γ-Fe2O3→BaFe12O19 (4.2)

(i) Effect of calcinations temperature

Heat treatment was carried out to promote crystallization and to investigate the

effect of calcinations on the structural changes of barium hexaferrite. The combusted

BaFe12O19 powder was divided into four parts; they were calcined in air for 4 hours at

different temperatures 250 oC, 500

oC, 950

oC and 500

oC followed by 950

oC

respectively using a muffle furnace.

(ii) Effect of Swift Heavy Ion irradiation on BaFe12O19 hexaferrite powder

It is known that irradiation of solids with energetic particle beams leads to

creation of wide variety of defect states. Swift heavy ions, which are in the range of

MeV under different conditions, can produce additional defects, create phase



transformations and give rise to anisotropic growth to some materials. Swift heavy ion

irradiation of material is a unique tool to modify the properties of the material and it

provides an alternative to photons for introducing electronic excitations into the

material. During the last two decades, the swift heavy ion (SHI) irradiation in

magnetic oxides and ferrites has been studied to understand the damaged structure and

the modifications on their physical, magnetic and dielectric properties [9].

In order to study the effects of Swift Heavy Ion (SHI) irradiation on structural,

surface morphology and magnetic properties of material, the prepared M-type Barium

hexaferrite (BaFe12O19) powder was irradiated with 200 MeV Ag16+

ions at a fluence

of 1 x 1013

ions/cm2 using 15UD Pelletron Accelerator at Inter University Accelerator

Centre, New Delhi. The electronic energy loss, nuclear energy loss and range of the

200 MeV Ag16+

ion beam were calculated using TRIM/SRIM calculations [10].

(iii) Preparation of BaFe12O19 hexaferrite powder in presence of cationic

surfactant cetyltrimethylammonium bromide (CTAB)

Surfactants (cationic, anionic and non-ionic) are amphiphilic materials

containing a polar long-chain hydrocarbon “tail” and a polar, usually ionic “head”

[11]. They can play an important role in synthesizing the material in different

interesting morphologies. In order to study the effect of cationic surfactant - CTAB on

the particle size, microstructure, magnetic and dielectric properties of sample,

BaFe12O19 hexaferrite powder was also prepared in the presence of

cetyltrimethylammonium bromide (CTAB) (Merck, GR grade). Aqueous solution of

0.1 M CTAB was prepared with minimum amount of double distilled water and then

the metal nitrates were dissolved in the same solution. Further procedures followed

were same as the previous one till the combustion process. The combusted powder

was calcined at 500 oC followed by 950

oC for 4 hours each.

4.2.2 Synthesis of doped M-type barium hexaferrite powder using

Sol-gel auto combustion technique

Barium hexaferrite BaFe12O19 (M-type) has a complex hexagonal unit cell and

belongs to the magnetoplumbite structures, space group P63/mmc. The arrangement

of the 12 Fe3+

ions in the unit cell is as follows: two ions in the tetrahedral sites (four

nearest O2-

neighbors), nine ions in the dodechedral sites (six nearest O2-

neighbors)



and one ion in the hexagonal site (five nearest O2-

neighbors). Materials of this type

have a strong uniaxial magnetic direction, making as permanent magnets. A large

amount of researches has been realized to modify the magnetic properties of barium

hexaferrite by substitution of Fe3+

ions with other trivalent cations or divalent and

tetravalent cation combinations and/or Ba2+

ion by other cations [12-15]. The

magnetic properties of substituted ferrites depend directly on both electronic

configuration and preference to occupy the non-equivalent Fe3+

sublattices of the

substituted cations on hexagonal structure.

Replacing Fe3+

ions by other less magnetic moment, paramagnetic or

diamagnetic cations leads to change in the exchange interactions between the

magnetic sublattices and to the appearance of new positions of Fe3+

ions. It causes

reduction of the high uniaxial anisotropy field of the Ba ferrite. In present work two

types of substitution, one with diamagnetic element (Cu) and another one with

paramagnetic element (Al) were carried out. Effects of cationic substitution on

structural, magnetic and dielectric properties were investigated.

Synthesis of BaCuxFe12-xO19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) hexaferrite powder


(Sigma Aldrich, > 98 % purity), Cupric nitrate, Cu(NO3)2 (Merck, GR grade), Citric

acid, C6H8O7 (Merck, GR grade), Aqueous (0.91 g/cm3) solution of NH4OH (Merck ,

GR grade) were used as starting materials. The molar ratio of metal nitrates to citric

acid was taken as 1:1. The metal nitrates were dissolved together in a minimum

amount of double distilled water to get a clear solution. An aqueous solution of citric

acid was mixed with metal nitrates solution, then ammonia solution was slowly added

to adjust the pH at 7. The mixed solution was kept on to a hot plate with continuous

stirring at 80 oC. When finally all water molecules were removed from the mixture,

the viscous gel began frothing. After few minutes, the gel automatically ignited and

burnt to form brown-colored powder. The obtained combusted powders were

precalcined at 500 oC followed by final calcinations at 950

oC for 4 hours each.

Synthesis of BaAlxFe12-xO19 (x = 0.4, 0.8, 1.2, 1.6, 2.0) hexaferrite powder


(Sigma Aldrich, > 98 % purity), Aluminium nitrate, Al(NO3)3 (Merck, GR grade),



Citric acid, C6H8O7 (Merck, GR grade), Aqueous (0.91 g/cm3) solution of NH4OH

(Merck , GR grade) were used as starting materials. The appropriate amount of

nitrates and citric acid as fuel was first dissolved into double distilled water to form a

mixed solution. The molar ratio of nitrates to citric acid is 1:1. The pH value of

solution was adjusted to about 7 using aqueous ammonia solution. Then, the mixed

solution was poured into a dish and heated at 80 oC under constant stirring to

transform into a dried gel. The dried gel simultaneously burnt in a self-propagating

combustion manner until it was completely transformed into loose powder. To get

ordered hexaferrite powder, combusted powders were precalcined at 500 oC followed

by final calcinations at 950 oC for 4 hours each.

4.2.3 Preparation of hexa-spinel (Ba2Ni2Fe12O22 / CuFe2O4) ferrite

composites

The magnetic properties of the magnetic materials are determined by both

intrinsic magnetic and microstructural properties. As a consequence, grain size,

particle shape, grain boundary type, etc. are important parameters. Energy product as

a combination of magnetization and coercivity essentially determines the merit of the

permanent magnets. Soft magnetic materials usually have relatively high

magnetization, while most of hard magnets have high coercivity, but quite low

magnetization. Combining a high saturation magnetization of the soft phase and a

high coercivity of the hard phase will have a large energy product and superior

magnetic properties [16-18]. In present work, hexa-spinel ferrite composites of the

two constituent phases Ba2Ni2Fe12O22 and CuFe2O4 were reported.

Synthesis of Ba2Ni2Fe12O22 hexaferrite powder

Aqueous solutions of barium nitrate Ba(NO3)2 (Merck, GR grade), Iron

nitrate, Fe(NO3)3.9H2O (Sigma Aldrich, > 98 % purity), and Ni(NO3)2 (Merck, GR

grade) were reacted with aqueous Citric acid, C6H8O7 (Merck, GR grade) solution in

1:1 molar ratio. pH value of mixed solution was increased to 7 by addition of NH4OH

(Merck , GR grade). The neutralized solution was evaporated very slowly over a

period of a few hours to dryness using hot plate. As soon as the solvent removal is

completed dried precursor undergoes a self-ignition reaction to form a very fine

powder. The obtained fine powder was preheated in a furnace at 500 °C for 4 hours



and then calcinated at 950 °C for 4 hours in order to achieve Ba2Ni2Fe12O22

hexaferrite particles.

Synthesis of CuFe2O4 spinel ferrite powder

In a typical procedure for the preparation; Fe(NO3)3.9H2O (Sigma Aldrich, >

98 % purity), and Cupric nitrate, Cu(NO3)2 (Merck, GR grade) were taken in

stoichiometric proportions then dissolved in a minimum amount of double distilled

water. Solution of Citric acid, C6H8O7 (Merck, GR grade) was added to the aqueous

salt solution in the ratio of 1:1 to total moles of nitrate ions and pH of the solution was

adjusted to 7.0 with addition of NH3.H2O. The solution was heated at 80 °C with

continuous stirring and maintained at constant temperature using a hot plate. Finally,

as water evaporated the solution became viscous and formed a very viscous brown

gel. Continuous heating led to the ignition of the gel. The dried gel burnt in a self

propagation combustion manner until all gels are completely burnt out to form a loose

powder. The obtained powders were preheated in air at 500 °C for 4 hours and then

calcinated at 950 °C for 4 hours to achieve ferrite particles.

The two kinds of ferrite powders Ba2Ni2Fe12O22 and CuFe2O4 thus prepared

were physically mixed in different mass ratios (1:1, 1:2, 1:5, and 1:8). Then mixed

powders were calcined at 800 oC for 4 hours in a muffle furnace.

4.2.4 Preparation of magnetoelectric (BaFe12O19 / BiFeO3) composites

The combination of both ferromagnetic and ferroelectric materials in a single

phase material is expected to produce new properties such as magnetoelectric [19]. A

material has magnetoelectricity when there is induction of magnetization by an

electric field or of polarization by a magnetic field [20]. This effect takes place in

mixed or compound materials that have ferro-piezoelectric and magnetoestrictive

phases and results from the linking of both phases. The selection of ferrite and

ferroelectric materials depends on the various factors like high magnetostriction

coefficient, piezoelectric coefficient, high dielectric permeability and poling strength

[21]. Bismuth ferrite (BiFeO3) and M-type barium hexaferrite (BaFe12O19) were

chosen for the preparation of magnetoelectric composite. Bismuth ferrite is one of the

very few multiferroic materials with a simultaneous coexistence of ferroelectric with



high Curie temperature (Tc = 810 - 830oC) and antiferromagnetic order (below

TN = 370 oC) parameters in perovskite structure.

In the first step, BiFeO3 was prepared by using Sol-gel auto combustion

technique. Bismuth nitrate, Bi(NO3)3 (Merck, GR grade), Iron nitrate,

Fe(NO3)3.9H2O (Sigma Aldrich, > 98 % purity), Citric acid, C6H8O7 (Merck, GR

grade) and 25 % (0.91 g/cm3) aqueous solution of NH4OH (Merck , GR grade) were

used as starting materials. Since bismuth nitrate is insoluble in water, initially it was

dissolved in diluted nitric acid to get clear solution. Iron nitrate, citric acid and

ammonia were added in the solution as per the procedure, and then the neutralized

solution was kept in hot plate at 80 oC to get combusted powder. The combusted

powder was annealed at 500 oC to get ordered bismuth ferrite.

The BiFeO3 thus obtained was added with already prepared BaFe12O19

hexaferrite powder in different weight percentage (25%, 50% and 75%) of BiFeO3.

Then mixed powders were calcined at 500 oC for 4 hours in a muffle furnace.

4.2.5 Synthesis of polyaniline / Ba2Ni2Fe12O22 composites using in situ

polymerization method

Organic-inorganic composites with an organized structure provide a new

functional hybrid between organic and inorganic materials. Incorporation of inorganic

constituents and organic polymeric materials combine the advantages of the inorganic

materials (mechanical strength, modulus and thermal stability) and the organic

polymers (flexibility, dielectric, ductility and processibility), which are difficult to

obtain from individual components [22,23]. Conducting polymers, a unique class of

materials that exhibit electrical and optical properties of metals or semiconductors,

have presented a great prospects for practical applications due to their unparalleled

architectural diversity and flexibility, inexpensiveness, and easiness of synthesis.

They have attracted significant attention in recent decades because of their potential

applications in various fields such as electromagnetic interference (EMI) shielding,

rechargeable battery, chemical sensor, corrosion devices and microwave absorption

[24,25].

Among conducting polymers, polyaniline (PANI) is probably the most widely

studied because it has a broad range of tunable properties derived from its structural



flexibility and some advantages like good environmental stability, easy preparation in

aqueous solution and organic solvents, performance stability, unique optical,

electrical, electrochemical properties [26]. The combination of the magnetic material

with conducting polymer leads to formation of ferromagnetic conducting polymer

composite possessing unique combination of both electrical and magnetic properties.

This work addresses the synthesis and characterization of polyaniline / Ba2Ni2Fe12O22

nano composite by in situ polymerization method with different aniline/

Ba2Ni2Fe12O22 weight ratios (1:1, 1:2 and 2:1).

Fig. 4.2. Schematic representation for the preparation of Polyaniline / Ba2Ni2Fe12O22 composites.



Aniline, C6H5NH2 (Merck, GR grade), Ammonium persulfate, (NH4)2S2O8

(Merck, GR grade), 0.1M HCl solution and prepared Y-type hexaferrite

(Ba2Ni2Fe12O22) were taken as raw materials. In typical procedure, certain amount of

ferrite powder was suspended in minimum amount of 0.1 M HCl and vigorously

stirred at room temperature for 1 hour to get fine aqueous dispersion. Aniline

monomer was then added to the suspension, the composite ratios of aniline and ferrite

in weight were 1:2, 1:1 and 2:1. The monomer-ferrite dispersion was stirred for

2 hours, and cooled to 0 – 5 oC. Stoichiometric amount of ammonium persulfate

(molar ratio aniline: (NH4)2S2O8 was 1:1) was dissolved in minimum amount of 0.1M

HCL and then slowly drop by drop added in to the suspension mixture with a constant

stirring. The polymerization was allowed to proceed for 10 hours at 0 – 5 oC after

which, the solution was dark green. Finally, the composites were obtained by filtering

and washing repeatedly with 0.1 M HCl and large amount of distilled water. The wet

polyaniline coated particles were then dried at 60 oC for 24 hours.

Synthesis of Polyaniline / Ba2Ni2Fe12O22 composites in presence of cationic,

anionic and non-ionic surfactants

In order to study the effect of surfactants on the particle size, microstructure,

magnetic and dielectric properties, polyaniline / Ba2Ni2Fe12O22 composites were

prepared in the presence of different surfactants using in situ polymerization method.

Three different surfactants CTAB, SDS and Tween-80 (cationic, anionic and non-

ionic, respectively) were used for making preparing three polyaniline / Ba2Ni2Fe12O22

composites. Initially, certain amount of ferrite powder was added in aqueous solution

of surfactant and constantly stirred at room temperature for 2 hours. Aniline monomer

was then added to the suspension, the molar ratio of aniline and surfactant was 1:2.

After adding (NH4)2S2O8, the solution was allowed for polymerization for 10 hours.

Polyaniline-surfactant-Ba2Ni2Fe12O22 composites were obtained by filtering and

washing repeatedly with 0.1 M HCl and large amount of distilled water, and dried at

60 oC for 24 hours.

4.3 Characterization

Following instrumental techniques have been used for the characterization of

synthesized samples.



4.3.1 Structural properties

(i) FTIR analysis

Fig. 4.3. FTIR Brucker tensor spectrometer model no. 27

In present work, Fourier transformed infrared spectra (FTIR) was recorded at

room temperature in the wave number range from 4000 to 400 cm-1

with potassium

bromide (KBr) as solvent using a FTIR Brucker tensor spectrometer model no. 27.

FTIR spectra were taken to identify OH or NO group and residual carbon presence in

the sample during synthesis process. It can be eliminated by sintering the samples at

high temperature. One more importance of taking these spectra was to confirm ferrite

formation by locating two major absorption bands in the range 600 - 550 cm-1

and

450 - 400 cm-1

[27,28,29]. These two bands are found to be in agreement with the

characteristic infrared absorption bands for the metal oxygen stretching vibrations of

hexaferrite.

Initially hexaferrie/composite sample-KBr mixed pellet was made using a

hydraulic press. A small amount of sample is mixed and ground with about hundred

times its mass of potassium bromide. The mixture is transferred to an evacuuable die,

to remove the moisture and then a high pressure is applied to yield a transparent

pellet. It is put in a suitable holder and the whole assembly is placed in the line of the

infrared beam.



(ii) X-ray Diffraction

Fig. 4.4. X-ray Difractometer (SEIFERT XRD 3000PTS)

X-ray diffraction patterns of calcinated hexaferrite/composite samples were

recorded at room temperature on a Model: SEIFERT XRD 3000PTS using CuKα

radiation (λ=1.5405 Ǻ). A full scan of 2θ from 20o to 80

o was carried out at a

scanning speed of 2º /min. XRD patterns were recorded on a plotter to identify the

crystal structure and phase formation. In present work, XRD patterns were indexed

using the software Powder X and Full proof suite. The indexed patterns were

compared with those in the JCPDS (Joint Committee on Powder Diffraction Standard)

data base for phase identification.

Parameters calculated from XRD measurement:

Unit cell volume

Cubic (4.3)

Tetragonal (4.4)

Hexagonal (4.5)



Trigonal (4.6)

Orthorhombic (4.7)

Monoclinic (4.8)

Triclinic V = abc (1-cos2 α - cos

2 β - cos

2 γ) + 2(cos α cos β cos γ)

½ (4.9)

4.3.2 Morphology

Fig. 4.5. Scanning Electron Microscope (LEO 440i)

The microstructures of calcined hexaferrie/composite samples were examined

via Scanning Electron Microscope, SEM. LEO 440i SEM, equipped with NORAN

X-ray microanalysis system and semafore digitizer was used for this purpose. Ferrites

are have high resistive materials, so they do not provide a path to ground for the

specimen current (Is) and may undergo electrostatic charging when exposed to the

electron probe. Therefore, the local charge on the specimen can be positive or

negative. Negative charge presents a more serious problem, as it repels the incident

electrons and deflects the scanning probe, resulting in image distortion or fluctuations

in image intensity [30]. To prevent charging problem, the specimen are coated with

thin layer of gold using Ion-sputter coater. Micrographs of every sample are taken at

different magnification level from micrometer to nanometer.



Characteristic Information obtained from SEM images:

Grain size

Surface roughness

Porosity

Particle size distributions

Material homogeneity

Intermetallic distribution and diffusion

4.3.3 Magnetic properties

Field dependent magnetization measurements of synthesised

hexaferrie/composite materials were carried out at room temperature using EG & G

Princeton Applied Research VSM Model 4500 system. ~10 mg of powder sample was

tightly filled in a small non-magnetic plastic tube and mount on the VSM sample

holder, and then the hysteresis curve had been recorded between the magnetic fields

of 15 K Oe. The magnetic parameters that are most often used to characterize the

magnetic properties of magnetic media obtained from hysteresis loop: Saturation

magnetization (Ms), Remanent magnetization (Mr), Coercivity field (Hc) and

Squareness ratio (Mr / Ms).

Fig. 4.6. Vibrating Sample Magnetometer (EG & G Princeton Applied Research, Model 4500)



4.3.4 Dielectric properties

Dielectric measurement was carried out in the frequency range from 20 Hz to

2 MHz at room temperature by using an Agilent E-4980A precision LCR meter. The

LCR meter uses the “Capacitive Method” for obtaining relative permittivity by

measuring the capacitance of a material that is sandwiched between parallel

electrodes. The simultaneous measurements of capacitance (Cp) and equivalent

parallel resistance (Rp) were taken in 201 linear steps for the frequency range 20Hz to

2 MHz. The samples for dielectric measurement were pressed by applying a pressure

of 5 tonnes to get compact circular pellets with dimensions 13 mm in diameter and

approximately 0.5 mm to 2 mm in thickness. Air gap, which is formed between the

material under test and the electrodes, can be a primary cause of measurement error.

In order to eliminate the air gap, the pellets were coated with silver paste on both

sides.

Fig. 4.7 Agilent E-4980A precision LCR meter

Dielectric parameters calculated from the measurement:

Capacitance without sample

(4.10)

Dielectric constant (real part)

(4.11)

Dielectric constant (imaginary part)

(4.12)



Loss factor

(4.13)

Where,

εo - Permittivity in free space = 8.854 x 10-12

F/m

A - Area cross-section of pellet

t - Thickness of pellet

f - Frequency of the applied field

Cp - Capacitance with sample

Rp - Equivalent parallel resistance



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