Symmetry breaking in single-crystal SrTiO3 plates: EPR manifestations

Results of the electron paramagnetic resonance (EPR) studies of Fe3+ and Mn4+ impurity centers in high-quality single-crystal SrTiO3 plates with thickness are presented. Impurities served the paramagnetic probes of the crystal structure. Analysis of the collected data indicates that the symmetry of the crystal structure of thin (001) and (110) oriented strontium titanate plates above lowers in the bulk from the cubic to tetragonal. The structure of this high-temperature tetragonal state is different from that of the conventional low-temperature antiferrodistorsive phase and has not been reported for SrTiO3 before. It is shown that the effect does not originate from the residual stress; its magnitude and particular manifestations depend on plate orientation, surface quality and geometry of a sample. Peculiarities of the observed phenomenon are presented and the possible scenario of its realization is discussed.