The asymmetrical next-nearest neighbor lattice gas model was used to describe the oxygen-vacancy phase diffusion on the basal plane of 123 YBaCuO superconducting ceramics at low temperatures. A finite value Q for the trapping potential barrier was added. The Monte Carlo technique was used to obtain the components of the (tracer) diffusion coefficient. The character of its dependence on the coverage was shown to vary, from convex at high temperatures to concave at lower ones. The temperature of the transition depended on the trapping barrier height. The activation energy (obtained from an Arrhenius plot) was seen to be varying as a function of coverage and the trapping barrier, and was not symmetrical with respect to c = 0.5 if Q was finite. The same of course was true for the diffusion coefficient. The value of the "final-state-energy" was reported and compared to the ground-state energy. This indicates the likely occurrence of fine structure at specific coverage values corresponding to a predicted devil's staircase distribution of superstructure phases. The time evolution of twins was also reported. The limited validity of the model for describing the 123 structural phase diagram was pointed out.

Monte Carlo Simulation of Oxygen Diffusion in Planar Model of 123 YBCO Low-Temperature Regime and Effect of Trapping Barrier. A.Pȩkalski, M.Ausloos: Physica C, 1994, 226[1-2], 188-98