Dynamic Jahn-Teller effect of an impurity in a spontaneously distorted crystal

The local symmetry of Ti4+ sites in SrTiO3 is known to be cubic above 106°K, and tetragonal below. We have investigated the electron-spin- resonance spectrum of substitutional Ni3+ in the tetragonal phase of this compound. The components of the g tensor are observed to vary monotonically from g=2.215 and gII=2.103 at 4°K, to gII=g=2.180 at 106°K. Three models of the dynamical Jahn-Teller effect in the presence of coupling to strain are examined. The magnitude and temperature dependence of g-gII are best explained by a model in which the g tensor is given by a Boltzmann average over the two lowest vibronic states. The tunneling splitting appears to exceed by far the maximum spontaneous splitting of these states (23 cm-1). Our results indicate that the elongation of the nearest-neighbor octahedron is too small to be the principal cause of the g splitting. © 1970 The American Physical Society.