Monte Carlo study of tracer and chemical diffusion of oxygen in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+2\mathit{c}}$

Tracer and chemical diffusion of oxygen in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+2\mathit{c}}$ has been studied by Monte Carlo simulations of an asymmetric next-nearest-neighbor Ising model. Striking differences between tracer and chemical diffusion are found and explained by the effect of the thermodynamic factor, which is determined also by Monte Carlo simulation. Especially for c=0.5, the effect of the thermodynamic factor is large. It is also found that tracer diffusion in the ordered orthorhombic phase of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+2\mathit{c}}$ is strongly anisotropic, which is explained in terms of different diffusion mechanisms.