Thermogravimetric and High-Temperature X-Ray Studies on the Orthorhombic-to-Tetragonal Transition of YBa2Cu3Oy

Abstract

Thermogravimetric experiment was performed to determine oxygen content in the high T _c superconductor YBa₂Cu₃O _y . The y varies from 5.8 to 6.5 depending on temperature and oxygen fugacity, indicating that the average valence of copper ions is between 2 and 1. The oxygen content is strongly affected by quenching process of a sample. High-temperature X-ray diffraction study showed orthorhombic-to-tetragonal transition (second or possibly higher order) at around 900 K. Combining this fact with the thermogravimetric data, we concluded that the compound having y less than ∼6.0 has a tetragonal symmetry.