Oxygen ordering and Fe configuration in reduced and re-oxidized YBa₂Cu₃-_xFe_xO_y

Abstract

Bulk samples of YBa₂Cu₃-_xFe_xO₇-δ (x = 0.09 and x = 0.36) were produced by a conventional sintering method. Transmission electron microscopy studies show that after reduction and subsequent low-temperature re-oxidation of the sintered sample, the orthorhombicity of the sample increases drastically. The strongly ‘tweed’ morphology changed into a strongly twinned one with weak tweed contrast. A two-dimensional lattice-gas model is established to study the effect of reduction and subsequent low-temperature re-oxidation on the oxygen ordering and Fe distribution in these systems. Monto Carlo simulations using Kawasaki dynamics are performed to investigate the Fe cluster formation and its effect on oxygen ordering for various Fe concentrations. The results are in very good agreement with experiments, suggesting that the structure change during the reduction and reoxidation process can be explained by Fe clustering in CuO plane.