HIGH-TEMPERATURE HF-SITE-INTERCHANGE CHEMISTRY IN LINBO3 AND LITAO3

We explain observed Hf-site interchange in LiNbO3 and LiTaO3 at high temperatures using solid-state defect chemistry reactions. The model takes into account fully the effects of nonstoichiometry on the ferroelectric-to-paraelectric phase transition. Specifically, we use this model to interpret the temperature dependence of the Hf-site interchange that we measured using perturbed-angular-correlation (PAC) spectroscopy. In this context, the site interchange is an equilibrium, thermodynamic process that involves the partitioning of Hf ions between Li and group-V (Nb and Ta) sites. The Hf ions replace group-V ions by pushing them from their normal sites to the Li sublattice. Based on the temperature dependence of the site occupancy, this reaction requires approximately 2.2 to 2.3 eV.