Dielectric and thermal anomalies in the raraelectric state of litaO₃ related materials

Dielectric and thermal measurements show an anomaly above the ferroelectric Curie temperature, T_c, for stoichiometric LiTaO₃ crystal and various stoichiometric LiTaO₃ related ceramics: a maximum at temperatures close to 1130K appears in each curve for the thermal dependence of both permittivity and Cp. The corresponding value of ε'_r at 1130K is much higher than that of ε'_rat T_c. A thermal X-ray diffraction study performed on a LiTaO₃ single crystal seems to indicate that the observed anomaly is due to the formation at 1130K of LiTa₃O₈ at the crystal surface following the decomposition reaction: 3LiTaO₃ → LiTa₃O₈ + Li₂O.