The effect of trigonal and tetragonal stresses on the model Jahn-Teller system Y²⁺:SrCl₂

The effect of externally applied stresses of e_g and t_2g symmetry on the cubic E_g(X)e_g Jahn-Teller (JT) system Y²⁺ in SrCl₂ is studied. Coupling constants were obtained with the aid of EPR and by relying on a Ham-type cluster JT Hamiltonian, in conjunction with a random strain distribution. This is established from a critical review of the contributing strain sources (including possible percolation effects due to the isotopic composition of natural SrCl₂). The stress of t_2g symmetry shows strong effects. The authors conclude that the cubic Ham factor q is nearly one and that the experiments allow, as a function of this latter stress, one to pass gradually towards a trigonal JT effect. The optical absorption spectrum assigned to Y²⁺ is given in addition.