Dielectric properties and phase transitions of SrTiO₃-KTaO₃ system

Abstract

Dielectric spectra of epsilon' and epsilon `` (5-300 K, 100 Hz-10 MHz) of (SrTiO3)(x)(KTaO3)(1-x) are studied with the most successfully prepared x = 0.85 composition. A wide epsilon'(T) maximum at 43 K (43 kHz) is observed. Losses reveal the additional relaxations in the 4.6-9.8 K and 176-247 K regions. Of most importance is, that Curie-Weiss behavior is replaced by relaxation below the temperature of epsilon'(T) maximum. That is the ergodic homogeneous ordering turns on a glass-like behavior below 43 K. The above can be understood as an antiferroelectric phase transition, but a glass-like order-disorder transition at 18 K looks more preferable. The cooperative hopping reorientation of electron and hole polarons originating due to charge transfer, as the cause of dielectric relaxation, resulting in the polaronic reorientation freezing and glass-like state at 18 K within SrTiO3, and an another possible one at 2 K within KTaO3 dominated regions are considered. This model is supported by dielectric and infra-red absorption with SrTiO3:Ta crystals, where absorption at 2000 cm(-1) is suggested to be due to polarons.