To the antisymmetrical next-nearest neighbor Ising model of oxygen diffusion in YBa2Cu3O6+x was added the possibility of an oxygen atom jumping not only to the nearest neighbor but also to a next-nearest neighbor site via a jump that was entirely in the ab-plane. The usual Monte Carlo simulation procedure was used to calculate the tracer diffusion coefficient, which turned out to be less sensitive to the oxygen content than in the standard antisymmetrical next-nearest neighbor Ising model, as found by experiment. The Arrhenius plots revealed an almost linear behavior. Also calculated was the average energy per particle in the system. When plotted as a function of oxygen concentration, this yielded information concerning possible phase transitions in the system. At low temperatures, diffusion probably occurred along the copper-oxygen chains whereas, for higher temperatures and low concentrations of oxygen, inter-chain diffusion as well as reorientation of short oxygen chains was possible.

Model of Oxygen Diffusion in YBa2Cu3O6+x with Next-Nearest-Neighbor Hopping: a Monte Carlo Study. M.Ausloos, A.Pekalski: Physical Review B, 1995, 52[6], 4577-82