TDPAC study of structural disorder in metamict zircon

Time-differential perturbed angular correlation spectroscopy (TDPAC) was used to characterize the electric field gradient of zircon in the metamict and partially recrystallized state. TDPAC spectra were recorded of various samples originating from Australia using 181Ta probe nuclei. The disorder of the metamict state is reflected by broadening of the TDPAC spectral lines. Spectra recorded of samples as received show linewidths as high as 12%. No significant change in the linewidths was observed after isochronal annealing between 200 and 600°C. Annealing above 600°C reduces the spectral linewidths, indicating the beginning of an ordering process. The annealing temperature required to result in a specific linewidth was found to be correlated with the samplesʹ U and Th impurity concentrations. Calculations based on a simple point charge model are used to relate TDPAC linewidths to random displacements of atoms in the structure of zircon in the metamict and the partially annealed state.