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

To the antisymmetric next-nearest-neighbor Ising (ASYNNNI) model of ox ygen diffusion in YBa2Cu3O6+x we have added a possibility for an oxyge n atom to jump not only to a nearest neighbor but also to a next-neare st-neighbor site through a jump remaining in the ab plane. The usual M onte Carlo simulation procedure has been used to calculate the tracer diffusion coefficient which turns out to be less sensitive to the oxyg en content than in the standard ASYNNNI model, as found out in experim ents. The Arrhenius plots show nearly linear behavior. We have also ca lculated the average energy per particle in the system. This when plot ted as a function of oxygen concentration yielded some information abo ut possible phase transitions in the system. At low temperatures the d iffusion is probably taking place along the copper-oxygen chains where as for higher temperatures and low concentration of oxygen, interchain diffusion as well as reorientation of short oxygen chains is also pos sible.