Tracer and chemical diffusion of oxygen in YBa2Cu3O6+2c was studied by Monte Carlo simulations of an asymmetrical next-nearest-neighbor Ising model. Striking differences between tracer and chemical diffusion were found and explained by the effect of the thermodynamic factor, which was also determined by Monte Carlo simulation. Especially for c = 0.5, the effect of the thermodynamic factor was large. It was also found that tracer diffusion in the ordered orthorhombic phase of YBa2Cu3O6+2c was strongly anisotropic, which was explained in terms of different diffusion mechanisms.

Monte Carlo Study of Tracer and Chemical Diffusion of Oxygen in YBa2Cu3O6+2c. E.Salomons, D.De Fontaine: Physical Review B, 1990, 41[16], 11159-67