THE SUPERCONDUCTIVITY OF YBa 2 Cu 3 O 7-δ SYSTEM WITH TRANSITIONAL STRUCTURE FROM TETRAGONAL PHASE TO ORTHORHOMBIC PHASE

Abstract

The intermediate YBa2Cu3O7-δsamples of single phase with transitional structure from tetragonal phase to orthorhombic phase are prepared by quenching at different temperatures and investigated systematically. From X-ray diffraction (XRD), R-T curve and ac susceptibility measurements, it can be concluded that the structure transits from tetragonal phase to orthorhombic phase as the quenching temperature decreases; the YBa2Cu3O7-δ samples with tetragonal phase are nonsuperconductive till 4.2K; the critical temperature depends on the degree of orthorhombic distortion in the intermediate samples; the possible existence of a structure phase transition near 100K for the non-superconductive tetragonal phase is discovered for the first time. The electrical conductance property at high temperature region (higher than 100K) for the samples quenched at higher temperature can be explained in terms of the affection of oxygen vacancies.