PAC analysis of defect motion by Blume's stochastic model forI=5/2 electric quadrupole interactions

Using Blume's stochastic model and the approach of Winkler and Gerdau, we have computed time-dependent effects on perturbed angular correlation (PAC) spectra due to defect motion in solids in the case ofI=5/2 electric quadrupole interactions. We report detailed analysis for a family of simple models: “XYZ+Z” models, in which the symmetry axis of an axial EFG is allowed to fluctuate among orientations alongx, y, andz axes, and a static axial EFG oriented along thez axis is added to the fluctuating EFGs. When the static EFG is zero, this model is termed the “XYZ” model. Approximate forms are given forG ₂(t) in the slow and rapid fluctuation regimes, i.e. suitable for the low and high temperature regions, respectively. Where they adequately reflect the underlying physical processes, these expressions allow one to fit PAC data for a wide range of temperatures and dopant concentrations to a single model, thus increasing the uniqueness of the interpretation of the defect properties. Application of the models is illustrated with data from a PAC study of tetragonal zirconia.