Dielectric investigations of solid solutions SrTiO$_3$–KTaO$_3$ and SrTiO$_3$–KNbO$_3$

The temperature dependences of the dielectric constant and dielectric hysteresis loops in ceramic samples of $(1-x)$SrTiO$_{3-x}$KNbO$_3$ and $(1-x)$SrTiO$_{3-x}$KTaO$_3$ (0 $\le x\le$ 0.3) solid solutions prepared using different heat treatments have been investigated. Phase diagrams of the studied solid solutions have been constructed in the $T$–$x$ coordinates. It has been shown that, after quenching of samples (spontaneous cooling at room temperature after long-term heating at the sintering temperature of the ceramic samples), the temperature of the induced phase transition increases because of the weakening of random electric fields associated with nonisovalent impurities due to their “frozen” nonequilibrium redistribution. For small concentrations $x$, strong dielectric relaxation is observed in the temperature range of 150–250 K. A model of relaxing centers, which is based on the local charge compensation of heterovalent impurities, has been proposed.