Charge transport in high-temperature superconducting Bi-Sr-Ca-Cu-O ceramics

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CHARGE TRANSPORT IN HIGH-TEMPERATURE SUPERCOND UCTING Bi-Sr 一 Ca-Cu ・ o CERAMICS

by

URVIJA SINHA Department of Physics

Thesis submitted

in fu

げ

ilment of the requirements of the degree of

DOCTOR OF PHILOSOPHY

to the

INDIAN INSTITUTE OF TECHNOLOGY, DELHI

INDIA

I 992

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CERTェ^F工^CATE

This is 七o cer七^{i fy}七^ha七七^he 七hesis en七ⁱ七led !I Charge Transpor七 in High T自nperature Superconducting Bi一Sr-Ca-Cu-C Ceramics1' being submi七七ed by Ms. Urvija Sinha 七。七he Indian Ins七^itu七^{e of} Technology, Delhi, for 七he award of Doc七or of Philosophy in Physics is a record of bonafide research work carried ou七 by her.

Ms. Urvija Sinha has worked under our guidance and supervision and has fulfilled 七he requiremen七 ^for 七he submission of 七^his 七^hesis.

The resul七s ob七ained in 七^his 七hesis have no七 been submitted, in par七 or full, to any o七her universi七^{y or ins}七ⁱ七^u七ion for 七he award of any degree or diploma.

(Dr . D . C . Dube) (Dr. s .C . Ma七hur) Professor of Physics Professor of Physics

Indian Ins七 i七 ute of

Technology Indian Ins七i七ute of Technology

New Delhi一 110 016,

INDIA. New Delhi一110 016, INDIA .

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ACKNOWLEDGMENT

I七 is my great pleasure to be associated with Prof. s.C.

Mathur and Prof・. D. C. Dube,my supervisors. My sincere thanks go to them for their invaluable guidance,stimulating discussions and constant encouragement throughout the course of the work.

I ^would also・ like 七o 七hank the teachers of Physics departmen七 specially Dr . v . D . Vankar Prof . D . P . Tewari、^{Prof .}

D . K . Roy、 Prof. R.G. Nendiratta and Prof. R.K. Puri who helped me at different junctions of work.

Dr .

Y. s.

Reddy of NPL helped me a lot in initial stages of work . I feel highly grateful to hi皿 and also to Dr. R.G. Sharnia and his group members for their help.

I am greatly indebted to Mr. I.C. Mathur and members of the Microwave Group、 SSPL (Delhi) specially Dr. Pran Kishan and Ma七^heru for helping me in let七ing use the necessary facili七^y 七heir labora七ory.

My colleagues, friends and all the members of my group were big help

r n f M ・

1

0

cooperation a七 thanks are due Prabhakar Rao

七o nie in providing necessary assistance and all times. I am thankful to all of them. Special 七o Sobhanath for her constant moral support and

and D. S. Rawat for their whole一hearted support during the last stage of the work.

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瓦

y thanks

are also due to

Mr. p.N.

^Tiwari ^(Physics

Department) for helping with the XRD measurements and Mr. D.C.

Sharma (Textile Technology Department) and Dr. Chhatar Singh

(ITMNEC)

for helping with the SEM measurements. I would like to thank Mr. N.S. Gupta for making neat tracings of figures and staff of Eagle Computing Centre for helping in typing of the manuscript . I also thank the s七^{aff of} 七he Physics depar七^{ment who} were of help to me in various stages of work.

on my personal level、 I received constant support、 encouragement and love from my parents, my parents-in-law, my husband,Atul and my relatives. 工 am grateful to all of them.

磁ナ磁右 (Urvija Sinha)

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8 2 l 2

25

CONTENTS

Page No.

CHAPTER I GENERAL INTRODUCTION AND SYNOPSIS OF

THE THESIS i

References li

REVIEW OF HIGH TEMPERATURE SUPERCONDUCTIVITY Introduction

High temperature superconduc如rs:a class apart from conventional superconductors

2.2.i Theories of high temperature superconductors

2.2.2 General features of high temperature superconductors

Properties of Bi一Sr-Ca一Cu-C system

Synthesis of Bi一Sr一Ca一Cu-O superconductors

2.4.i Effectiveness of Pb一substitution for the synthesis of high-Tc phase

2.4.2 Growth mechanism of high-T,.. phase in

CHAPTER II

2 . i 2.2

2 .3 2 .4

13

15

29 Bi(Pb）一Sr-Ca-Cu-C system

2.4.3 Methods used for synthesis of bulk superconducting materials

2.5 Characterization of superconducting samples 2.6 』 Microwave studies in high temperature

superconductors 2.7 Surface impedance

2.7.1 Surface impedance in conventional superconductors

2.7.2 Surface resistance measurements on high temperature superconductors

2.7.3 Surface resistance dependence on microstructure

31

一j 7 3 3

1

4 4 4

45 47

49

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5 5 6 6 8 8 6 6 0 1 7 7 2 3 7 7 8 8 8 8 0 3 9 9

2.7.4 Surface reactance measurements on high temperature superconduc七^ors

2.8 Dielectric study of high temperature superconductors

References

CHAPTER III EXPERIMENTAL TECHNIQUES

3.i Introduction

3.2 Method of sample preparation

3. 3 Sample characterization techniques

3.3.i DC resistance measurement technique 3.3.2 XRD measurement technique

3.3.3 AC susceptibility measurement technique 3.3.4 SEM measurement technique

3.4 Microwave measurement technique

51

2 4 5 5

3 . 4 . i 3 . 4 . 2

Cavity perturbation technique Microwave measurement set-up

4 9 7 7

References 83

CHAPTER IV RESULTS AND DISCUSSION

にharacterization Measurements)

4 . i Introduction ⁸⁶

4 . 2 Justification of sample preparation 4 . 3

technique Selection

used

of fabrication parameters

6 7 8 8

4 . 4 Characterization by dc resistance measurements 4.4.i General features of R-T curves

4 . 4 .2(a) Effect of Pb-concentration

4 . 4 .2(b) Discussion of the effect of Pb-doping

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4.4.3(a) Effect of sintering time

4.4.3(b) Discussion of the effect of sintering t une

4.5 Results of XRD measurements

4.5.i Indexing of diffraction peaks

4.5.2 General features of X-ray diffractographs 4.5.3 Determunation of percentage volume of

high-Te phase

4.5.4 XRD results of pre一sintered samples 4.5.5 A critique of the method used for the

determination of volume fraction of high-Te phase

4.6 Results of AC susceptibility measurements

4.6.i Characteristic features of x、-T curves 4 . 6.2 エnterpretation of <'-T curves

4.7 Discussion of XRD and AC susceptibility results 4.7.i Discussion of XRD results

4 . 7 . 1(a) Effect of Pb-concentration 4,7.1(b) Effect of sintering time

4・⁷・1(c) Important features from XRD data 4.7.2 Discussion of AC susceptibility results

4 . 7 . 2(a) Effect of Pb-concentration 4.7.2(b) Effect of sintering time 4・7・2(c) Important features from AC

susceptibility data 4.8 Characterization by SEM measurements References

95

5 7 9 9 97

loo loo 102

102 104 106 108 109 109 109 112 113 114 114 116

i 17 118 120

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CHAPTER V RESULTS MID DISCUSSION (Microwave Measurements) 5.i Introduction

5.2 Method used for microwave measurements:

a justification

5.3 Evaluation of geometric factor,G 一． ^s 5.4 Q、s of the cavity

5.5 Surface resistance

5.5.1 Results and discussion of surface resistance measurements

5.5.2 加。-fluid model and BCS theory of impedance

5.5.3 Effect of synthesis parameters on resis七^ance

5.6 Surface reactance References

surface surface

124

126 128 133 150

150

156

164 171 178