Dielectric-Related Optical Line Shifts in SrTiO3:Cr3+

Abstract

Very unusual and large shifts of the $R$ lines of ${\mathrm{Cr}}^{3+}$ with temperature and applied electric fields were observed. Below the tetragonal transition temperature, these shifts were found to have a behavior similar to that of the reciprocal dielectric constant of SrTi${\mathrm{O}}_3$. The electric field shift is shown to be due to the ionic polarization induced by the electric field. The $R$-line thermal shift cannot be explained by the usual theory of interaction with the acoustic lattice modes. The temperature dependence of the dielectric constant and the $R$-line shift is discussed in terms of interaction with the low-frequency optical-phonon branch. The tetragonal transition of SrTi${\mathrm{O}}_3$ at 107°K is instrumental in producing a discontinuity in the slope of the $R$-line shift versus temperature.