The possibility of O atom jumps, not only to a nearest-neighbor but also to a next-nearest neighbor site (via jumps that remained within the ab-plane), was incorporated into the anti-symmetrical next-nearest neighbor Ising model for O diffusion in this material. The usual Monte Carlo simulation procedure was used to calculate the tracer diffusion coefficient. This was found to be less sensitive to the O content than it was in the case of the anti-symmetrical next-nearest neighbor Ising model; in agreement with experiment. The Arrhenius plots exhibited an almost linear behavior. Calculations were also made of the average energy per particle in the system. When plotted as a function of the O concentration, this yielded information concerning possible phase transitions in the system. It was suggested that, at low temperatures, diffusion probably occurred along the Cu-O chains whereas, at higher temperatures and low O concentrations, inter-chain diffusion as well as the reorientation of short O chains was possible.

M.Ausloos, A.Pekalski: Physical Review B, 1995, 52[6], 4577-82