Mössbauer Study of the SrTiO3:Co57System

Abstract

The Mössbauer investigation of the SrTi${\mathrm{O}}_3$:${\mathrm{Co}}^{57}$ system has indicated the coexistence of low-spin ($d{\epsilon }^5$) and high-spin ($d{\epsilon }^{3}d{\gamma }^2$) ferric states, in contrast to the EPR studies which have shown that iron enters the SrTi${\mathrm{O}}_3$ lattice at the ${\mathrm{Ti}}^{4+}$ site in its high-spin trivalent ($d{\epsilon }^{3}d{\gamma }^2$) state. The relative intensities of the low-spin high-spin ferric states could be altered by thermal treatment. In highly reduced samples, high-spin ferric ($d{\epsilon }^{3}d{\gamma }^2$) and high-spin ferrous ($d{\epsilon }^{4}d{\gamma }^2$) states have been observed with an associated charge-compensating oxygen vacancy. The cubic-tetragonal phase transition at 110°K, caused by the accidental degeneracy of longitudinal acoustic and transverse optical modes, has been detected through the temperature variation of isomer shift of the high-spin ferric state.