Nucleation and growth kinetics of the tetragonal to orthorhombic transition in YBa2Cu3O7−∂

Abstract
The nucleation and growth geometry of the tetragonal to orthorhombic transformation in YBa2Cu3Ox is determined to be grain‐boundary nucleation after saturation. In this geometry the orthorhombic phase rapidly nucleates along the grain boundaries, then propagates into the grains as a planar front governed by the much slower volume diffusion of oxygen. This conclusion is reached by fitting the volume fraction of the superconducting, and hence orthorhombic, phase as a function of annealing time at 400 °C to the Avrami relation. The volume fraction of the superconducting phase is obtained using magnetization versus field data.