Ultrasonic Determination of the Jahn–Teller Effect Parameters in Impurity-Containing Crystals

A method is developed to determine the symmetry properties of strains and the type of Jahn–Teller effect in crystals with impurity ions in a triply degenerate electronic T state. This method is based on a calculation of the isothermal contribution of the impurity subsystem to the elastic moduli of a crystal and the absorption and velocity of normal modes for all three possible problems, namely, T ⊗ e, T ⊗ t₂, and T ⊗ (e + t₂). The calculation results are compared with experimental data. The efficiency of the method is demonstrated for a CdSe:Cr²⁺ crystal. The CrSe₄ center is found to be described in terms of the problem T ⊗ e. The parameters of the ground-state adiabatic potential are determined.