Breaking of the Cubic Symmetry in Millimeter-Size SrTiO3 Crystals: ESR Manifestations

Abstract

The found effect of lowering the symmetry of the crystal structure of thin (less than 1 mm) plates and bars of strontium titanate (SrTiO3) single crystals is discussed. This symmetry lowering manifests itself in the electron spin resonance (ESR) spectra of impurity centers (Fe3+and Mn4+ions, used as paramagnetic probes). It is shown that symmetry lowering is observed at temperaturesT 105 K, which generally correspond to the cubic phase of SrTiO3; it leads to the formation of a tetragonal nonpolar structure, differing from the antiferrodistortive (AFD) phaseD4ℎ18, which is characteristic of strontium titanate atT 105 K and was not observed previously in SrTiO3. The factors determining the distortion value are found to be the geometry and ratio of sample sizes, surface finishing quality, and crystallographic orientation of plates.