MODEL OF OXYGEN DIFFUSION IN YBA2CU3O6+X WITH NEXT-NEAREST-NEIGHBOR HOPPING - A MONTE-CARLO STUDY

To the antisymmetric next-nearest-neighbor Ising (ASYNNNI) model of oxygen diffusion in YBa2Cu3O6+x we have added a possibility for an oxygen atom to jump not only to a nearest neighbor but also to a next-nearest-neighbor site through a jump remaining in the ab plane. The usual Monte Carlo simulation procedure has been used to calculate the tracer diffusion coefficient which turns out to be less sensitive to the oxygen content than in the standard ASYNNNI model, as found out in experiments. The Arrhenius plots show nearly linear behavior. We have also calculated the average energy per particle in the system. This when plotted as a function of oxygen concentration yielded some information about possible phase transitions in the system. At low temperatures the diffusion is probably taking place along the copper-oxygen chains whereas for higher temperatures and low concentration of oxygen, interchain diffusion as well as reorientation of short oxygen chains is also possible.