PREPARATION CONDITIONS AND

CHARACTERIZATION ON YBCO BASED

SUPERCONDUCTORS

Selda OKUMU

July, 2004

ZMR

PREPARATION CONDITIONS AND

CHARACTERIZATION ON YBCO BASED

SUPERCONDUCTORS

A Thesis Submitted to the

Graduate School of Natural and Applied Sciences of

Dokuz Eyll University

In Partial Fulfillment of the Requirements for

the Degree of Master of Science in Physics

by

Selda OKUMU

July, 2004

ZMR

iii

ACKNOWLEDGMENTS

I wish to express my sincere graditude to my supervisor Prof. Dr. Kemal KOCABA,

who introduce me with scienfic research. This study has been completed by his continual

encouragement an invaluable guidance.

I am indebted to Prof. Dr. Muhsin FTOLU for SEM microphotographs and

Assoc. Prof. Ltfi ZYZER for AC susceptibility measurements all throughout the

work. I can not forget the helps of Dr. Yusuf SELAMET.

I am also grateful to Assoc. Prof. Filiz ERCAN in Hacettepe University for her

support in taking XRD patterns.

I also thank to Gnl BLGE, Ebru KI and Enis DARILMAZ for close friendships

and their encouragements.

Finally, my deepest gratitude goes to my family for their love and support.

Selda OKUMU

iv

ABSTRACT

YBCO was the first material found to be superconducting above nitrogen temperature.

It exhibits a very interesting and complex relationship between its chemistry, crystal

structure and physical properties. A very subtle electronic charge balance exists between

the one dimensional cooper-oxygen chains, which have variable oxygen content and the

two dimensional cooper-oxygen pyramidal planes, where superconductivity originates. In

oxygen deficient YBCO, oxygen is removed from the CuO chains. Related to this, 90 K

superconductor is obtained for 0< x

v

Elements that were taken part in YBCO system were also observed in EDAX analysis,

too. In addition, densities of bulk samples were measured by the help of density kit.

In the light of these measurements, we concluded that preparation conditions and

addition ratios were quite important on superconductivity. It was realized that using of

cupric acetate instead of CuO in YBCO ceramics effected superconducting properties

negatively. Also it was noticed that smaller ratio amounts of Ni should be added to

YBCO system, as Ni was magnetic dopants.

vi

ZET

Sv azot scaklnn zerinde speriletken olan ilk materyal olarak YBCO

bulunmutur. Kimyas, kristal yaps ve fiziksel zellikleri arasnda ok ilgin ve

karmak bir balant bulunmaktadr. Deiken oksijen ieriine sahip bir boyutlu bakr-

oksijen zincirleri ile speriletkenliin olutuu iki boyutlu bakr-oksijen piramitsel

dzlemler arasnda ok g alglanan bir elektronik yk dengesi olumaktadr. Oksijen

eksiklii bulunan YBCOda CuO zincirlerindeki oksijen yapdan ayrlmtr. Buna bal

olarak, 90 Kda speriletkenlik 0 < x < 0.2 iin, 60 Kda ise 0.3 < x < 0.55 speriletkenlik

ve de 0.55 < x

vii

belirlendi. YBCO sisteminde yer alan elementler de EDAX analizlerinden belirlenmi

oldu. Ayrca bulk halindeki rneklerin younluklar younluk lm sistemi ile lld.

Bu lmlerin nda, hazrlama koullarnn ve katk oranlarnn speriletkenlikte

olduka nemli olduu sonucuna ulald. YBCO seramiklerde, CuO yerine bakr asetatn

kullanlmas speriletkenlik zelliklerini olumsuz etkiledii anlald. Bunun yannda Ni

manyetik bir katk olduundan daha dk katklama oranlarnda YBCO sisteminde

kullanlmas gerektii anlalmtr.

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CONTENTS

Page

Contents ....viii

List of Tables ...xi

List of Figures ... xii

Chapter One

INTRODUCTON

1.1 Discovery of Superconductivity ..1

1.2 Brief History of Superconductivity 2

Chapter Two

PHENOMENOLOGY OF THE SUPERCONDUCTVTY

2.1 The Meissner Effect ...7

2.2 London Theory ...9

2.3 The Thermodynamics Of The Superconducting Phase Transition .11

2.4 Superconductors In Magnetic Fields (Type I and Type II) ..14

2.5 Ginzburg-Landau Theory ...................................................................................19

2.6 BCS Theory ...23

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Chapter Three

HIGH TEMPERATURE SUPERCONDUCTORS

3.1 Crystal Structure of the High TC Cuprates ..29

3.2 Processing of High Temperature Superconductors .32

3.2.1 Processing of Bulk Superconductors 33

3.2.1.1 Processing YBCO 123 Bulk Superconductors 34

3.2.2 Processing of HTS Thin Films ...40

3.3 Influence of Dopants 41

3.3.1 Effects of Ni ..42

Chapter Four

EXPERMENTAL DETAILS

4.1 How to Prepare a Superconductor? ...43

4.2 AC Susceptibility Measurements 44

4.3 X-Ray Diffraction Analyses .46

4.4 Scanning Electron Microscope (SEM) Measurements .48

4.5 Density Measurements .50

x

Chapter Five

EXPERIMENTAL RESULTS

5.1 Characterization of Y(123)+wt% Superconductors Prepared by Conventional

Solid-State Reaction Technique ....52

5.1.1 XRD Analysis ...52

5.1.2 AC Measurement Results ...56

5.1.3 SEM Microphotographs .........59

5.1.4 Density Measurements and Porosity .....62

5.2 Characterization of Y(123)+wt% Superconductors Prepared by Different

Condition .....63

5.2.1 XRD Analysis .......63

5.2.2 AC Measurement Results ...66

5.2.3 SEM Microphotographs .....68

5.2.4 Density Measurements and Porosity .....71

Chapter Six

CONCLUSION

6.1 General Conlusion 73

Appendix A ..77

References ......78

xi

List of Tables

Table 2.1 Differences between Type I and Type II superconductors...........................18 Table 5.1. Lattice parameters, bulk density, oxygen content and porosity values for

YBa2Cu3O + wt% Ni samples ........................................................................................53

Table 5.2. Lattice parameters, bulk density, oxygen content and porosity values for

YBa2Cu3O + wt% Ni samples ......................................................................................64

xii

List of Figures

Page Figure 1.1 Resistance of a mercury sample at low temperature 1

Figure 1.2 The evolution of the critical temperature with time .6

Figure 2.1 The Meissner effect of a superconductor .8

Figure 2.2 The temperature depedence of the critical field of a superconductor ...9

Figure 2.3 The temperature dependence of the L ...11

Figure 2.4 The temperature dependence of the entropy of the two states .......................13

Figure 2.5 Specific heat of superconductor has a large discontinuity and tends to zero at

T = 0 ..14

Figure 2.6 The penetration depth and the temperature dependence of a Type-I

superconductor ..15

Figure 2.7 The temperature dependence of a Type-II superconductor 16

Figure 2.8 London penetration depth and coherence length in a N-S interface ...17

Figure 2.9 The shematic diagrams of the Ginzburg-Landau assumptions ...22

Figure 2.10 Schematic diagram of a Cooper pair 24

Figure 2.11 There is a time-retarded, effective attraction between two electrons in a

crystal lattice (virtual electron-phonon interaction) ..25

Figure 2.12 (a) Fermi energy Level and distribution (b) Energy gap of 2 occurs at the

Fermi energy EF ...26

Figure 3.1 The crystal structure of La2CuO4. (a) The arrows on the coppers denote the 3d

orientation of the spins in the antiferromagnetic state (b) shows the copper and oxygen

orbitals in the plane ...........................................................................................................29

Figure 3.2 Structure of YBa2Cu3O7-. The fivehold coordination of the Cu in the copper

oxide plane and the distortion of the CuO2 planes are also shown ...................................30

xiii

Figure 3.3 The temperature profiles for (a) the melt texturing growth and

(b) the melt process melt growth ......................................................................................37

Figure 3.4 Shematic representation of microstructure evolution in the MPMG growth of

YBCO: (a)after quenching-yttria and solidified liquid; (b)during heating to the 211+L

region; (c)in the 211+L region; and (d) final microstructure showing the 123 and 211

phases 37

Figure 4.1 AC susceptibility measurement hand-made system to determine critical

temperature ...45

Figure 4.2 Illustration of conventional X-ray diffraction system 47

Figure 4.3 Shematic diagram of the SEM functions 50

Figure 5.1 X-ray diffraction patterns of the YBa2Cu3O + wt% Ni superconducting

samples. o BaCuO2, Ba2CuO3, CuO phases ......................................................55

Figure 5.2 AC susceptibility-temperature characteristics for YBa2Cu3O + wt% NiO

ceramic superconductors [A(x=0.00 wt%) B(x=1.00wt%) C(x=2.00wt%) D(x=3.00wt%)

E(x=4.00wt%)] prepared by conventional solid-state reaction method 58

Figure 5.3 SEM microphotographs of fracture and surface of YBa2Cu3O + wt% NiO ..61

Figure 5.4 Density-porosity dependent amount of Ni addition ........................................62

Figure 5.5 X-