Adiabatic potential energy surface of the Jahn-Teller complexes in SrF2:Cr2+ crystal

Abstract

Temperature dependence of attenuation of ultrasonic transverse normal modes, polarized propagating along the [110] crystallographic axis in SrF2 crystal doped with Cr2+ ions was measured at the frequency of 52–162 MHz in the temperature range of 4–180 K. The results indicated the T2g⊗(eg + t2g) Jahn-Teller effect problem with important impact of quadratic term in the vibronic Hamiltonian. The value of activation energy was derived from the temperature dependence of relaxation time of the sub-system of the Jahn-Teller complexes simulated with account of three mechanisms of relaxation: thermal activation, tunnelling through the potential energy barrier, and two-phonons mechanism similar to Raman scattering. The extrema points of adiabatic potential energy surface: six orthorhombic global minima, three tetragonal and four trigonal saddle points were calculated in 5-dimensional space of symmetrized coordinates.