Abstract
The orthorhombic‐to‐tetragonal transition at ambient temperature in YBa2Cu3Oy ceramics is empirically mapped as a function of oxygen content (y) based on published neutron and x‐ray diffraction studies. On approaching the transition region (y∼6.5) from the orthorhombic phase, there is a noticeable anomaly in the c‐axis length, a smooth evolution of the b axis, and a rather abrupt transition of the a axis (the axis along which oxygen deficiency obtains at larger values of y in the orthorhombic phase). Finally, the empirical method developed here for ascertaining oxygen content from crystallographic data is compared to neutron, hydrogen reduction, and iodometric titration results for several metastable YBa2Cu3Oy ceramics and Fe‐ and Co‐doped materials.