"PREPARATION AND STUDY OF HIGHT SUPERCONDUCTORS"

Abstract

This project has been directed towards investigations on the preparation and study of the new high temperature superconductors. Various types of superconducting materials (e.g. Yttrium and Bismuth based) were prepared under a variety of conditions and finally a suitable (Melt-Textured-Growth) process was idPnlified as the method which delivered the best quality samples. 'rhe samples were characterized according Lo t.h e i r- c r i t.ical temperatures, (where they lose all electrical resistance), magnetjzation behaviour, and transport propertjes ,1nder. varying conditions of magnetic fields and currents. In these studies most of which are the first of their kind in Pakistan, we were able to identify the important parameters which lim i L U1e ab i I i ty of these materials to carry large currPnls and Lo withstand high magnetic fields. It was df'lerminPd LhaL grain boundaries and absence of directional order in polycrystalline materials are the major drawbacks. The melL LexLured superconductors prepared by us provided very good i n t.o r-g r a i n conlacts, large grains and well defined d j rec 1. i o n a l j Ly. The last feature, viz. directionality enabled us Lo study Lheir uniqu? two dimensional behaviour. A number of interesting and important features were observed in Lhe anisotropy of their magnetic responses, which also illustrate the complexity of their behaviour. Measurements of magnetization changes with time, were performed which yiPlded further insight into the dynamical behaviour of Lhese materials, and the role of defects in enhancing critical currents. The results obtained during the period of this project have been published ·internationally in the form of Eleven (11) research publications. Additionally they were presented in both local and international conferences and seminars. Seven experimental and two theoretical M.Phil Theses were completed on various aspects of this problem. Two experimental Ph.D? Theses are nearing completion. The principal InvestigaLor was awarded the A. Salam Prize in Physics for 1989 on the basis of some of the work done in this project. Finally, ?hese studies have an important bearing on our ability to understand the electrodynamics of the new high temperature superconductors, so as to enable their applications. Large critical currents, high critical fields and temperatures are

Lhe parameters whjch are crucial to the fabrication of super- conducting wires and thence to the fabrication of

superconouct.ing magnets.