Temperature dependence of the Ti-site electric-field gradient in titanite, CaTiSiO5

Using perturbed-angular-correlation (PAC) spectroscopy, we have measured nuclear-electric-quadrupole interactions at the Ti sites in ceramic samples of titanite that were doped with the '181181Ta PAC probe. Measurements were made over a temperature range from 10 to 980 K to investigate the effects of the antiferroelectric-to-paraelectric transition at approximately 500 K on the electric-field gradients (EFGs) at the Ti site. Near the transition temperature Tc, the magnitude Vzz of the EFG shows no significant inflections. Over the entire temperature range, Vzz decreases approximately linearly with increasing temperature, whereas remains relatively constant. The line-shape parameter ' decreases slowly with increasing temperature from 10 K to approximately Tc; at temperatures above Tc, ' remains relatively constant. Using a point-charge model, we attribute the absence of any discernible effects of the transition on the measured values of Vzz and to the direction and symmetry of the Ti-ion displacement relative to the Ti-site EFG axes.