Research Institute "Reactivelectron", Donetsk, Russia
Abstract:
The paper presents a study of the temperature dependence of the permittivity $\varepsilon(T)$ of quantum ferroelectrics KTaO$_3$ and SrTiO$_3$ and the solid solution based on them (SrTiO$_3$)$_{0.85}$ – (KTaO$_3$)$_{0.15}$ at temperatures from 5 to 300 K, for the description of which an exponential function with the Boltzmann probability factor and a self-consistent pre-exponential factor is used. It is shown that such an approach in the low-temperature quantum limit is consistent with the Barrett formula, and in the high-temperature limit - with the Curie-Weiss law. Based on this, the activation energies of the processes occurring in three selected temperature ranges (5–30; 30–80; 80–300 K) are determined, where the dependence $\varepsilon(T)$ has an exponential form. It is assumed that for KTaO$_3$ and SrTiO$_3$ such activation processes are caused by the temperature excitation of phonons when approaching the Debye temperature. For (SrTiO$_3$)$_{0.85}$ – (KTaO$_3$)$_{0.15}$ the deviation of the $\varepsilon(T)$ dependence at $T$ = 30–80 K from the exponential one is explained by phonon-phonon interactions of normal modes of crystal vibrations.
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