Distinction between Lattice and Cluster Models of the Jahn-Teller Effect in an Orbital Doublet

Abstract

Acoustic-paramagnetic-resonance and electric-field-induced thermally detected EPR measurements have been made in crystals of ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$: ${\mathrm{Ni}}^{3+}$. To reconcile theory with experiment, dynamic Jahn-Teller effects must be present, and, in addition, $2q-p$ is shown to be less than unity. This is the first reported example of an orbital doublet for which the multimode rather than the cluster model is needed.