Annealing treatment effects on structure and superconductivity in Y ₁Ba₂Cu₃O_9-x

We report the effects of heat treatment and ambient on the structure and superconducting properties of Y1Ba2Cu3O 9-x. The structure undergoes an orthorhombic-to-tetragonal transition on heating at about 700°C, caused by oxygen loss and disordering of oxygen vacancies on the copper plane between the barium layers. Heat treatments that promote maximum ordering of the oxygen vacancies result in superior superconducting properties.