Increased cubic-tetragonal phase transition temperature and resistivity hysteresis of surface vacuum annealed SrTiO3

Electrical properties of SrTiO3 single crystal samples treated by an anisotropic surface annealing technique under reducing conditions have been investigated in the temperature range of 35 K-300 K. Optical and atomic force microscopy show that annealing gives rise to polycrystallization and the formation of colored dendritic structures. Carrier concentrations and mobilities determined by Hall measurements as well as resistivities detected by van der Pauw measurements show the expected metallic behavior due to oxygen vacancy doping. Moreover, the temperature dependent resistivities indicate a cubic-to-tetragonal phase transition, which to our knowledge has not been reported before. Additionally, the transition occurred up to 53 K above the known bulk transition temperature TC at 105 K with a hysteresis up to a temperature of 220 K. Both phenomena possibly arise from dislocations and associated strain fields introduced by surface annealing that are assumed to lower the free energy of the tetragonal phase and simultaneously pin tetragonal domains. Thus, microregions of the tetragonal phase persist above TC causing the hysteresis in resistivity up to ∝12%. This effect possibly provides new chances for future oxide based non-volatile data-storage devices. (orig.)