Dielectric properties ofLiTaO3

The dielectric susceptibilities ${\chi }_{\mathrm{ii}}$ and conductivities ${\sigma }_{\mathrm{ii}}$ in ${\mathrm{LiTaO}}_3$ are measured over a broad temperature range up to 1200 K at frequencies up to 13 MHz. The dielectric properties are compared with previously published results on the elastic properties. Both the inverse-susceptibility difference between constant strain and constant stress (${\chi }_{\mathrm{ii}}^x$ ${)}^{\mathrm{-}1}$-(${\chi }_{\mathrm{ii}}^X$ ${)}^{\mathrm{-}1}$ and the elastic-constant difference between constant polarization and constant field $C_{\mathrm{ii}}^P$-$C_{\mathrm{ii}}^E$ are interpreted consistently in terms of both electrostrictive and higher-order interactions between the strain and polarization. The contribution of higher-order interactions to (${\chi }_{33}^x$ ${)}^{\mathrm{-}1}$ -(${\chi }_{33}^X$ ${)}^{\mathrm{-}1}$ and $C_{33}^P$-$C_{33}^E$ appears to be attributable to anharmonicity in the soft mode. Both ${\chi }_{33}$ and ${\sigma }_{33}$ exhibit significant dispersion over a wide temperature range, including $T_C$=868 K. This may be related with vacancies or Li ion motion. A comparison with light-scattering measurements suggests that the phase transition in ${\mathrm{LiTaO}}_3$ has an intermediate character between the displacive and order-disorder categories.