Oxygen ordering in the basal plane of YBa2Cu3Oz has been studied by Monte Carlo simulations of a two-dimensional anisotropic Ising model. The orthorhombic to tetragonal transition is found to be second order at high temperature in agreement with previous CVM calculations. At low temperatures, a cell-doubled orthorhombic phase appears near stoichometry z=6.5, intermediate between the single cell orthorhombic and tetragonal phases. At very low temperatures, long-lived transient OCuO chain ordering is observed to lead to triple and fivefold unit cells. Where not obscured by transient ordering, the transition lines bordering the orthorhombic cell-doubled phase are found to be second order. The observed equilibrium and non-equilibrium structures correlate well with atomic resolution micrographs and diffraction data from the YBa2Cu3Oz system.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering