REAL STRUCTURE AND ANOMALOUS OPTICAL PROPERTIES OF STRONTIUM TITANATE CRYSTALS. A.F. Konstantinova, L.A. Korostel' and S.N. Sulyanov. Institute of Crystallography, Russian Academy of Sciences, Leninsky pr. 59, Moscow 117333, Russia

The new defect (Ti(3+)-Vo complex) has been revealed in SrTiO3 crystals. The optical absorption at 620 nm, anomaly of ESR spectrum near the structure phase transition and luminescence at 645 nm have been associated with this defect. The model of this complex has been proposed. Absorption bands at wavelengths of 430 and 520 nm have been found in SrTiO3 crystals containing "blue spot" defects. These defects have been associated with the transition of some of the Ti(4+) ions to Ti(3+) state as well as with oxygen vacancies (Vo).

The powder patterns were found to contain additional very weak peaks (maximum intensity about 0.1% of that of the strongest 110 line) which in combination with all peaks of the cubic lattice presumably can be indexed in tetragonal unit cell. We suppose that the oxygen vacancies can make up some superstructure. Anomalous dichroism and birefringence have been detected. The dependence between the optical properties and real structure connected with oxygen non-stoichiometry has been determined. Such complexes as Vo, Ti(3+) ions, Ti(3+)-Vo clusters as well as doped clusters are supposed to form some additional order which can explain abnormal anisotropic optical properties of SrTiO3.