DEFORMATION SUPERSTRUCTURES, TWEED, AND OXYGEN-VACANCY ORDERING ASSOCIATED WITH PHASE-TRANSFORMATIONS IN YBA2CU3OZ

A theoretical technique is described, employing Monte Carlo simulation , which allows the investigation of strain effects associate-d with tr ansformations in solids. The method applies a grand canonical stress e nsemble in the study of elasticity during phase evolution in YBa2Cu3Oz where both oxygen occupancy and atomic positions in the basal plane, as well as total sample volume, can vary. Quenching experiments yield both metastable square-root 2a0 x square-root 2a0 superstructures from short-wavelength modulations and a tweed texture from long-period [11 0] modulations of the ordered z = 7.0 compound.