STRAIN AND DOMAIN EVOLUTION IN YBA2CU3OZ

A Monte Carlo study of the time evolution of atomic positions and occupancies within the basal plane of YBa2Cu3Oz is performed. The simulations are based upon an anisotropic Ising model, and, for the first time, include elastic interactions associated with continuous displacements of atoms within the basal plane. Samples quenched to temperatures below the disorder-order transition curve from the disordered tetragonal state rapidly form orthorhombic domains separated by twin boundaries' The resulting microstructure is observed to coarsen and eventually to anneal into a single domain that exhibits the experimentally observed 2 1/2 a0 X 2 1/2 a0 superlattice reflections. Strain maps are used to elucidate and interpret these observations.