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. UNIVERSITI PUTRA MALAYSIA ELECTRICAL CHARACTERIZATION OF Ca1-xAxCu3Ti4O12 (A = Sr OR Ba) WITH x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 CERAMICS. MAZNI BINTI MUSTAFA T FS 2008 49

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Page 1: MAZNI BINTI MUSTAFA - Universiti Putra Malaysiapsasir.upm.edu.my/5175/1/FS_2008_49A.pdf · Sifat ini dimodel menggunakan litar setara RC mengandungi tiga litar selari mangandungi

.

UNIVERSITI PUTRA MALAYSIA

ELECTRICAL CHARACTERIZATION OF Ca1-xAxCu3Ti4O12 (A = Sr OR Ba) WITH x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 CERAMICS.

MAZNI BINTI MUSTAFA

T FS 2008 49

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ELECTRICAL CHARACTERIZATION OF Ca1-xAxCu3Ti4O12 (A = Sr OR Ba) WITH x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 CERAMICS.

By

MAZNI BINTI MUSTAFA

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of

Science

Sept 2008

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DEDICATION

This special dedication goes to my family especially my beloved mother Faridah Amin, in remembrance of Mustafa Lakim, my brother, sister, relatives

and friends who have provided so much love, support, understanding and inspiration through the years.

ii

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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science.

ELECTRICAL CHARACTERIZATION OF Ca1-xAxCu3Ti4O12 (A = Sr OR Ba) WITH x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 CERAMICS.

By

MAZNI BT. MUSTAFA

Sept 2008

Chairman: Associate Professor W. Mohamad Daud W. Yusoff, PhD Faculty : Science CaCu3Ti4O12 (CCTO) has attracted an attention based on its extraordinary

dielectric properties and makes it applicable to a microelectronic device

application for capacitive element. Polycrystalline of CCTO, Ca1-xSrxCu3Ti4O12

(CSCTO) and Ca1-xBaxCu3Ti4O12 (CBCTO) with x = 0.1, 0.2, 0.3, 0.4 and 0.5

ceramics oxide were prepared using solid state reaction technique. The XRD

patterns for all samples show the single phase peak and the calculated lattice

parameter for CCTO is ’a’ = 7.3870 Å. The SEM images show that the grain

size was significantly increases with doping and consist of grain and grain

boundary.

The value of dielectric permittivity of CCTO at 1 kHz increases with

temperatures from 2740 at 70 oC to 3560 at 250 oC. The complex impedance

plot shows three semicircle arcs indicating that the electrical processes in the

iii

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material due to the contribution from the grain at high frequencies, the grain

boundary at intermediate frequencies and the electrode effect at low

frequencies. The behaviour was modeled using equivalent RC circuit consisting

of three parallel resistors, R and the universal capacitors, C*. The grain

resistance, Rg and the grain boundary resistance, Rgb decrease with

temperatures.

The conductivity plots for all the samples show two clear regions due to the

grain boundaries at low frequency and grain at high frequency. The value of n

obtained by fitting the grain region at high frequency dependent decreases with

temperatures with the value higher than 0.6 indicating that the conduction is

due to hopping of electrons among Ti4+ and Ti3+. A close similarity of the

relaxation and conductivity activation energy values indicates that the processes

may be attributed to the same type of charge carriers.

iv

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains.

SIFAT ELEKTRIK BAGI SERAMIK Ca1-xAxCu3Ti4O12 (A = Sr ATAU Ba) DENGAN x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5.

Oleh

MAZNI BT. MUSTAFA

Sept 2008

Pengerusi: Profesor Madya W. Mohamad Daud W. Yusoff, PhD Fakulti : Sains CaCu3Ti4O12 (CCTO) telah menarik perhatian berdasarkan sifat dielektrik yang

luarbiasa dan membuatkan ia boleh digunakan pada aplikasi alat

mikroelektronik bagi element kapasitif. Polikristal CCTO, Ca1-xSrxCu3Ti4O12

(CSCTO) dan Ca1-xBaxCu3Ti4O12 (CBCTO) dengan x 0.1, 0.2, 0.3, 0.4, dan 0.5

seramik oksida disediakan menggunakan teknik tindakbalas keadaan pepejal.

Corak XRD bagi semua sampel menunjukkan satu puncak fasa dan nilai

parameter kekisi bagi CCTO adalah ‘a’= 7.3870 Å. Imej SEM menunjukkan

saiz butiran meningkat dengan dop dan mengandungi butiran dan sempadan

butiran.

Nilai ketelusan dielektrik bagi CCTO pada 1 kHz meningkat dengan suhu dari

2740 pada 70 oC ke 3560 pada 250 oC. Plot impedans kompleks menunjukkan

tiga lengkungan separa bulatan yang menandakan proses elektrik di dalam

v

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bahan terjadi akibat dari sumbangan butiran pada frekuensi tinggi, sempadan

butiran pada frekensi pertengahan dan kesan elektrod pada frekuensi rendah.

Sifat ini dimodel menggunakan litar setara RC mengandungi tiga litar selari

mangandungi perintang, R dan kapasitor universal, C*. Kerintangan butiran Rg

dan kerintangan sempadan butiran Rgb meningkat dengan suhu.

Plot kekonduksian bagi semua sampel menunjukkan dengan jelas dua bahagian

disebabkan dari sempadan butiran di frekuensi rendah dan butiran di frekuensi

tinggi. Kawasan butiran pada frekuensi tinggi dimodel dan nilai n yang

diperolehi menurun dengan suhu dan nilainya adalah lebih dari 0.6

menunjukkan konduksi adalah disebabkan oleh loncatan oleh elektron di antara

Ti4+ dan Ti3+. Persamaan pada nilai tenaga pengaktifan santaian dan

kekonduksian menandakan bahawa proses adalah disebabkan oleh pembawa

cas yang sama.

vi

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ACKNOWLEDGEMENTS

First and foremost, I would like to extend my deepest gratitude to my

supervisor Assoc. Prof. Dr. W. Mohamad Daud W. Yusoff for all the help,

encouragement, advice and guidance. My sincere appreciation is also extended

to my co - supervisor Prof. Dr. Abdul Halim Shaari and Assoc. Prof. Dr. Zainal

Abidin Talib for their suggestions, recommendations and encouragement

during the period of this research. Working with them has provided me with a

vast understanding of materials science and theoretical knowledge which I will

continue to utilize in the future.

Many thanks to Mr. Walter Charles Primus, Mrs. Zalita Zainuddin, Miss Lee

Onn Jew, Science officer Mrs. Yusnita Osman and Mrs. Wan Yusmawati Wan

Yusoff, and my colleagues at Superconductor laboratory, Dielectric Properties

laboratory and also to all my postgraduate friends for their tremendous

assistance and sharing of numerous ideas throughout this study.

My greatest appreciation also goes to my family especially to my mother Mrs.

Faridah Amin, Mr. Mohamed Nasir Mohamed, Mr. Mohd Hafiz Mustafa and

Ms. Nabilah Huda Mustafa for their understanding, patience, encouragement

and prayers. Without them, the journey to the completion of this thesis will be a

lonely endeavour. I love all of you.

vii

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Finally, the financial support from the Ministry of Science, Technology and

Innovation (MOSTI), under the Fundamental Research grant vote no. 5523122

and Department of Physics, Universiti Putra Malaysia are also gratefully

acknowledged and appreciated.

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I certify that an Examination Committee has met on 19th September 2008 to conduct the final examination of Mazni Bt. Mustafa on her Master Science thesis entitled “Electrical Characterization of Ca1-xAxCu3Ti4O12 (A = Sr OR Ba) with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 Ceramics” in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows: AZMI ZAKARIA, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman) ZAINAL ABIDIN SULAIMAN, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Internal Examiner) HALIMAH KAMARI, PhD Faculty of Science Universiti Putra Malaysia (Internal Examiner) SININ HAMDAN, PhD Associate Professor Faculty of Engineering Universiti Malaysia Sarawak (External Examiner) HASANAH MOHD GHAZALI, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date:

ix

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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Master of Science. The members of the Supervisor Committee were as follows: W. MOHAMAD DAUD W. YUSOFF, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman) ABDUL HALIM SHAARI, PhD Professor Faculty of Science Universiti Putra Malaysia (Member) ZAINAL ABIDIN TALIB, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Member) HASANAH MOHD GHAZALI, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date: 30 December 2008

x

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DECLARATION I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously and is not concurrently submitted for any other degree at UPM or at any other institution.

MAZNI BT. MUSTAFA

Date: 19th September 2008

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TABLE OF CONTENTS

Page DEDICATION ii ABSTRACT iii ABSTRAK vii ACKNOWLEDGEMENTS ix APPROVAL x DECLARATION xi LIST OF TABLES xiv LIST OF FIGURES xv LIST OF ABBREVIATION/NOTATION/GLOSSARY OF TERMS xx CHAPTER 1 RESEARCH OVERVIEW 1.1 Introduction 1 1.2 Objective 3 1.3 Brief Literature 3 2 LITERATURE REVIEW

2.1 Introduction 5 2.2 Brief Literature on CaCu3Ti4O12 (CCTO) Ceramics

2.2.1 Structural Characterization 7 2.2.2 Dielectric Characterization 9

3 THEORY 3.1 Theory of Dielectric 17 3.2 Dielectric Polarization Mechanisms 20 3.3 Universal Capacitor Response 22 3.4 Complex Impedance Analysis 24 3.5 AC Conductivity 27

4 METHODOLOGY

4.1 Technique and Materials for Samples Preparation 29 4.2 Samples Characterization

4.2.1 X-Ray Diffraction (XRD) 32

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4.2.2 Scanning Electron Microscope (SEM) 32 4.2.3 Dielectric Measurement 32

4.3 Experimental Errors 34

5 RESULTS AND DISCUSSION

5.1 X-Ray Diffraction (XRD) 35 5.2 Scanning Electron Microscope (SEM) 38 5.3 Dielectric Characterization 40 5.4 Complex Impedance Analysis 46

5.5 Impedance Spectroscopy 69 5.6 AC Conductivity 74 5.7 Arrhenius Plot 83

6 CONCLUSION AND SUGGESTION

6.1 Conclusion 92 6.2 Suggestions 93

REFERENCES 95 BIODATA OF THE STUDENT 100 LIST OF PUBLICATION 101

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LIST OF TABLES Table Page 2.1 Dielectric and cell edge data for ACu3M4O12 phases (at 25 oC)

measured at 100 kHz (Subramanian, 2002)

11

3.1 Capacitance value and their possible interpretation (Sinclair et al., 2000)

27

5.1 Calculated lattice parameter and cell volume values for Ca1xSrxCu3Ti4O12 and Ca1-xBaxCu3Ti4O12 with different composition of x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5

37

5.2 The values of resistance and capacitance for the grain and the grain boundary for Ca0.8Sr0.2Cu3Ti4O12 and Ca0.5Sr0.5Cu3Ti4O12 ceramics

60

5.3 The values of resistance and capacitance for the grain and the grain boundary for Ca0.8Ba0.2Cu3Ti4O12 and Ca0.5Ba0.5Cu3Ti4O12 ceramics

68

5.4 The peak frequency values for CCTO and Ca1-xSrxCu3Ti4O12 and Ca1-xBaxCu3Ti4O12 with x = 0.2 and 0.5

74

5.5 Fitting parameters obtained from the grain conductivity at high frequencies region for Ca1-xSrxCu3Ti4O12 and Ca1-

xBaxCu3Ti4O12 with selected x = 0.2 and 0.5

81

5.6 The values of activation energies of the grain and the grain boundary Ea(g) and Ea (gb) for various composition of x in the system Ca1-xSrxCu3Ti4O12

85

5.7 Values of activation energies of the grain and the grain boundary Ea(g) and Ea(gb) for various composition of x in the system Ca1-xBaxCu3Ti4O12

85

5.8 The values of activation energies of the grain and the grain boundary relaxation time, Eaτ(g) and Eaτ (gb) for various composition of x in the system Ca1-xSrxCu3Ti4O12

90

5.9 Values of activation energies of the grain and the grain boundary relaxation time, Eaτ(g) and Eaτ (gb) for various composition of x in the system Ca1-xBaxCu3Ti4O12

90

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LIST OF FIGURES Figure Page 2.1 Unit cell of body-centered cubic CaCu3Ti4O12 in the Im-3 space

group

10

3.1 Capacitor (a) vacuum (b) filled with dielectric materials connected to a source of steady voltage

18

3.2 Contribution of the different polarization mechanisms to the frequency dependence of the relative permittivity

20

3.3 The polarization process with an electric field applied (a) space charge (b) dipole(c) ionic and (d) electronic polarization

22

3.4 (a) Complex impedance Z* plot. The semicircle arc is inclined at an angle nπ/2 (b) Circuit element representing the complex impedance plot in (a)

26

4.1 Schematic representation of the connections of The Novotherm units and the sample cell

34

5.1 X-ray diffraction pattern of Ca1-xSrxCu3Ti4O12 with x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 sintered at 1050oC for 24 hours

35

5.2 X-ray diffraction pattern of Ca1-xBaxCu3Ti4O12 with x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 sintered at 1050oC for 24 hours

36

5.3 SEM images for samples sintered at 1050 oC for 24 hours CaCu3Ti4O12

39

5.4 SEM images for samples sintered at 1050 oC for 24 hours Ca0.9Sr0.1Cu3Ti4O12

39

5.5 SEM images for samples sintered at 1050 oC for 24 hours Ca0.9Ba0.1Cu3Ti4O12

40

5.6 (a) Dielectric permittivity and (b) dielectric loss versus frequency for CaCu3Ti4O12 at frequency from 30 oC to 250 oC

42

5.7 (a) Dielectric permittivity and (b) dielectric loss versus frequency for Ca0.9Sr0.1Cu3Ti4O12 at frequency from 30 oC to 250 oC

43

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5.8 (a) Dielectric permittivity and (b) dielectric loss versus frequency for Ca0.9Ba0.1Cu3Ti4O12 at frequency from 30 oC to 250 oC

44

5.9 Complex impedance plane plots of CaCu3Ti4O12 ceramics at 70 oC with equivalent circuit modeling. Inset show grain semicircle at high frequency.

48

5.10 Complex impedance plane plots of CaCu3Ti4O12 ceramics at 90 oC with equivalent circuit modeling.

48

5.11 Complex impedance plane plots of CaCu3Ti4O12 ceramics at 130 oC with equivalent circuit modeling.

49

5.12 Complex impedance plane plots of CaCu3Ti4O12 ceramics at 170 oC with equivalent circuit modeling.

49

5.13 Complex impedance plane plots of CaCu3Ti4O12 ceramics at 210 oC with deconvoluted semicircle with equivalent circuit modeling.

50

5.14 Complex impedance plane plots of CaCu3Ti4O12 ceramics at 250 oC with equivalent circuit modeling.

50

5.15 Equivalent circuit of three parallel RC elements connected in series with series resistor, Rs.

51

5.16 Complex impedance plane plots of Ca0.8Sr0.2Cu3Ti4O12 ceramics at 70 oC together with fitted curve using equivalent circuit.

53

5.17 Complex impedance plane plots of Ca0.8Sr0.2Cu3Ti4O12 ceramics at 90 oC together with fitted curve using equivalent circuit. Inset show grain response at high frequency

53

5.18 Complex impedance plane plots of Ca0.8Sr0.2Cu3Ti4O12 ceramics at 130 oC together with fitted curve using equivalent circuit.

54

5.19 Complex impedance plane plots of Ca0.8Sr0.2Cu3Ti4O12 ceramics at 170 oC together with fitted curve using equivalent circuit.

54

5.20 Complex impedance plane plots of Ca0.8Sr0.2Cu3Ti4O12 ceramics at 210 oC together with fitted curve using equivalent circuit. Inset show the nonzero intercept at high frequency end.

55

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5.21 Complex impedance plane plots of Ca0.8Sr0.2Cu3Ti4O12 ceramics at 250 oC together with fitted curve using equivalent circuit

55

5.22 Complex impedance plane plots of Ca0.5Sr0.5Cu3Ti4O12 ceramics at 70 oC with equivalent circuit modeling.

57

5.23 Complex impedance plane plots of Ca0.5Sr0.5Cu3Ti4O12 ceramics at 90 oC with equivalent circuit modeling.

57

5.24 Complex impedance plane plots of Ca0.5Sr0.5Cu3Ti4O12 ceramics at 130 oC with equivalent circuit modeling.

58

5.25 Complex impedance plane plots of Ca0.5Sr0.5Cu3Ti4O12 ceramics at 170 oC with equivalent circuit modeling.

58

5.26 Complex impedance plane plots of Ca0.5Sr0.5Cu3Ti4O12 ceramics at 210 oC with equivalent circuit modeling.

59

5.27 Complex impedance plane plots of Ca0.5Sr0.5Cu3Ti4O12 ceramics at 250 oC with equivalent circuit modeling.

59

5.28 Complex impedance plane plots of Ca0.8Ba0.2Cu3Ti4O12 ceramics at 70 with equivalent RC circuit modeling.

61

5.29 Complex impedance plane plots of Ca0.8Ba0.2Cu3Ti4O12 ceramics at 90 oC with equivalent RC circuit modeling.

61

5.30 Complex impedance plane plots of Ca0.8Ba0.2Cu3Ti4O12 ceramics at 130 oC with equivalent RC circuit modeling.

62

5.31 Complex impedance plane plots of Ca0.8Ba0.2Cu3Ti4O12 ceramics at 170 oC with equivalent RC circuit modeling.

62

5.32 Complex impedance plane plots of Ca0.8Ba0.2Cu3Ti4O12 ceramics at 210 oC with equivalent RC circuit modeling.

63

5.33 Complex impedance plane plots of Ca0.8Ba0.2Cu3Ti4O12 ceramics at 250 oC with equivalent RC circuit modeling.

63

5.34 Complex impedance plane plots of Ca0.5Ba0.5Cu3Ti4O12 ceramics at 70 oC with RC circuit modeling.

64

5.35 Complex impedance plane plots of Ca0.5Ba0.5Cu3Ti4O12 ceramics at 90 oC with RC circuit modeling.

64

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5.36 Complex impedance plane plots of Ca0.5Ba0.5Cu3Ti4O12 ceramics at 130 oC with RC circuit modeling.

65

5.37 Complex impedance plane plots of Ca0.5Ba0.5Cu3Ti4O12 ceramics at 170 oC with RC circuit modeling.

65

5.38 Complex impedance plane plots of Ca0.5Ba0.5Cu3Ti4O12 ceramics at 210 oC with RC circuit modeling.

66

5.39 Complex impedance plane plots of Ca0.5Ba0.5Cu3Ti4O12 ceramics at 250 oC with RC circuit modeling.

66

5.40 Equivalent circuit of three parallel resistor and the universal capacitor elements.

67

5.41 Variation of imaginary part of impedance versus frequency for CCTO with equivalent RC circuit modeling at selected temperature.

69

5.42 Variation of imaginary part of impedance versus frequency for Ca0.8Sr0.2Cu3Ti4O12 with equivalent RC circuit modeling at selected temperature.

70

5.43 Variation of imaginary part of impedance versus frequency for Ca0.5Sr0.5Cu3Ti4O12 with equivalent RC circuit modeling at selected temperature.

70

5.44 Variation of imaginary part of impedance versus frequency for Ca0.8Ba0.2Cu3Ti4O12 with equivalent RC circuit modeling at selected temperature.

71

5.45 Variation of imaginary part of impedance versus frequency for Ca0.5Ba0.5Cu3Ti4O12 with equivalent RC circuit modeling at selected temperature.

71

5.46 Variation of imaginary part of impedance versus frequency for Ca0.5Ba0.5Cu3Ti4O12 at 210 oC with fitted line using equivalent RC circuit modeling and also show each fitted line correspond to the grain, grain boundary and electrode effect.

72

5.47 Conductivity plot of CaCu3Ti4O12 (CCTO) ceramic at various temperature.

75

5.48 Conductivity plot of Ca0.8Sr0.2Cu3Ti4O12 ceramics at 70 oC, 110 oC, 150 oC, 190 oC and 230 oC.

75

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5.49 Conductivity plot of Ca0.5Sr0.5Cu3Ti4O12 ceramics at 70 oC, 110 oC, 150 oC, 190 oC and 230 oC.

76

5.50 Conductivity plot of Ca0.8Ba0.2Cu3Ti4O12 ceramics at 70 oC, 110 oC, 150 oC, 190 oC and 230 oC.

76

5.51 Conductivity plot of Ca0.5Ba0.5Cu3Ti4O12 ceramics at 70 oC, 110 oC, 150 oC, 190 oC and 230 oC.

77

5.52 Circuit element represented by equation 5.1, which is used to model the ac conductivity curve

78

5.53 Frequency dependent conductivity vs. frequency for CCTO with high frequencies fitted line.

78

5.54 Frequency dependent conductivity vs. frequency for Ca0.8Sr0.2Cu3Ti4O12 with high frequencies fitted line.

79

5.55 Frequency dependent conductivity vs. frequency for Ca0.5Sr0.5Cu3Ti4O12 with high frequencies fitted line.

79

5.56 Frequency dependent conductivity vs. frequency for Ca0.8Ba0.2Cu3Ti4O12 with high frequencies fitted line.

80

5.57 Frequency dependent conductivity vs. frequency for Ca0.5Ba0.5Cu3Ti4O12 with high frequencies fitted line.

80

5.58 Arrhenius plot for the grain and the grain boundary conductivity of CaCu3Ti4O12 sample

84

5.59 Arrhenius plot for the grain and the grain boundary relaxation time of CCTO ceramic

87

5.60 Arrhenius plot for the grain and the grain boundary relaxation time of Ca0.8Sr0.2Cu3Ti4O12 ceramic

88

5.61 Arrhenius plot for the grain and the grain boundary relaxation time of Ca0.5Sr0.5Cu3Ti4O12 ceramic

88

5.62 Arrhenius plot for the grain and the grain boundary relaxation time of Ca0.8Ba0.2Cu3Ti4O12 ceramic

89

5.63 Arrhenius plot for the grain and the grain boundary relaxation time of Ca0.5Ba0.5Cu3Ti4O12 ceramic

89

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LIST OF ABBREVIATION/NOTATION/GLOSSARY OF TERMS

ε* Complex permittivity

ε' Dielectric permittivity

ε'’ Dielectric

σ Conductivity

σ(ω) Conductivity as a function of angular frequency

τ Relaxation time(sec)

χ’ Real part of dielectric susceptibility

χ” Imaginary part of dielectric susceptibility

ω Angular frequency

Ω Ohm

Å Angstrom

eV Electron volt

exp Exponential

f Frequency

i √-1

k Boltzmann constant

kHz Kilohertz

ln Natural logarithm

log Logarithm

Goes to

< Smaller than

> Bigger than

xx

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~ Approximately

Ac Alternating current

C* Complex capacitance

C’ Real part of capacitance

C” Imaginary part of capacitance

DC Direct current

Ea Activation energy

G Conductance

Hz Hertz

Im Imaginary part

K Kelvin

M* Complex modulus

M’ Real part of modulus

M” Imaginary part of modulus

R Resistance

Re Real part

UPM Universiti Putra Malaysia

V Voltage

XRD X-ray diffraction

Y* Complex admittance

Y’ Real part of admittance

Y″ Imaginary part of admittance

Z* Complex impedance

xxi

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xxii

Z’ Real part of impedance

Z” Imaginary part of impedance

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CHAPTER 1

RESEARCH OVERVIEW

1.1 Introduction

In recent years, colossal dielectric constant (CDC) materials exhibit high dielectric

constant ε’ value which greater than 1000 have attracted enormous of interests which

lead to significant advances in the miniaturization of electronic applications. In the last

few decades, microwave telecommunication and satellite broadcasting industries have

progressed greatly through portable telephones and have benefited greatly from the

miniaturization of various discrete components, especially the dielectric related

components such capacitors, resonators, filters and thus reduces the size of the devices.

The CDC materials usually found in oxide ceramics and widely used since the ceramics

processing are low in cost and reliable for electronic applications such capacitor. The

volume efficiency of a capacitor is directly related to its dielectric constant and there

have been an intensive researches on high dielectric constant materials since the higher

the dielectric constant, the more charge can be stored and smaller devices will be

produced.

In the former years the large dielectric response is a consequence of charge polarization

due to ferroelectric displacement of the central ion in the unit cell. The barium titanate

BaTiO3, are well known ferroelectric material for more than 50 years because of its high

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dielectric constant value which is in the range of 2000 to 10000 at room temperature

(Herbert et al., 1993). BaTiO3 have strong temperature dependence on ε' around the

transition temperature and has a ferroelectric transition to a tetragonal structure

accompanied by a rotation of the TiO6 octahedra at 393 K. This structural transition is

undesirable for many electronic device applications because it is often required that the

dielectric permittivity of the material to be constant over as wide a temperature range as

possible.

Recent scientific research and technical interest has attracted significant attention from

the discovery of colossal dielectric constant in CaCu3Ti4O12 (CCTO) ceramics. The

discovery of a room temperature cubic perovskite compound CCTO sparked the interest

in new materials that might not be limited by frequency and temperature. These

uniqueness properties allow broadly application in microelectronic component and plays

important role in creating high technology electronic devices.

CCTO was discovered in 1979 (Bochu et al., 1979) and reported to have high dielectric

constant exceeding 10,000 at 1 kHz (Subramanian et al., 2002) and show good

temperature stability from room temperature to 600 K. However, its dielectric constant

drop rapidly to less than 100 below 100 K. CCTO also has no structural transition as a

function of temperature and pressure in a cubic structure down to the lowest

temperature. Numerous researches have been carried out to explore its properties and to

probe the origin of the CDC. It is widely accepted that the CDC mechanism is extrinsic

in origin due to the electrically heterogeneous microstructure in CCTO ceramics

(Sinclair et al., 2002).

2