Determination of Oxygen Nonstoichiometry in a High-T_c Superconductor Ba₂YCu₃O_7-δ

Abstract

In order to elucidate the correlations between composition, structure and electrical properties of a high- T c superconductor Ba-Y-Cu-O system, thermogravimetric measurement and chemical analysis of oxygen nonstoichiometry were made at a temperature range of 350 to 1000°C and under the oxygen partial pressure of 10 -4 to 1 atm. Within a stability range of the composition Ba 2 YCu 3 O 7-δ , the oxygen deficiency, δ, was found to vary approximately from zero to 0.9, with associated mean valence of copper ions varying from 2.33 to 1.73. At a possible phase boundary region of tetragonal to orthorhombic crystal structures, no sign of discontinuity in δ was observed, suggesting its phase transition was of higher than a first order.