Mechanisms of structural anomaly and orthorhombic–tetragonal transition of YBa2Cu3Oy

Abstract

Powdered samples of oxygen-deficient YBa2Cu3Oy were annealed in various atmospheres at 880 and 300 °C to study the relations of structural anomaly, phase transition, and oxygen content. It was found that the structural anomaly in the c axis is reversible during oxygenation and deoxygenation. The change of the c axis arose from the electrical repulsion among Ba and Cu cations as oxygen was removed or refilled. The anomaly in the c axis occurred when the oxygen was further removed or refilled to a critical value, at which structural relaxation and electrical repulsion changed greatly. The phase transition is attributed to the anomalous change in the c axis, and the mechanism is proposed and discussed in this paper.