Ion channeling study of lattice distortions in chromium-doped SrTiO$_3$ crystals

The results of ion channeling studies of lattice distortions in SrTiO$_3$: Cr single crystals are presented. Two types of single crystals containing the same amount of Cr impurities but differing in stoichiometry have been investigated. The single crystals grown by the Verneuil method have the compositions of standard-grown SrTiO$_3$: Cr (0.05 at% Cr), whereas the single crystals grown with a strontium deficiency and a chromium compensating amount have the composition Sr$_{0.9995}$TiO$_3$ (0.05 at% Cr). Analysis of the angular channeling spectra indicates that, in crystals of both types, the main defects are Cr impurities located in octahedral sites. In the SrTiO$_3$: Cr crystals, impurity atoms manifest themselves as Cr$^{4+}$ with tetragonal Jahn-Teller distortions of the surrounding lattice. In the Sr$_{0.9995}$TiO$_3$: Cr crystals grown with a Sr deficiency, the characteristic displacements of Ti ions in the third coordination sphere of the Jahn-Teller center Cr$^{4+}$ exhibit the effect of interaction of the center with a neighboring vacancy in the Sr sublattice.