QUADRATIC-COUPLING PHONON-ASSISTED DEFECT TUNNELING THEORY APPLIED TO THE RBCL - AG+ OFF-CENTER SYSTEM

A model for the 110 off-center system RbCl: Ag+ including both linear and quadratic defect-lattice interactions is constructed. Model-parameter values are deduced from inelastic neutron scattering, infrared absorption, and electric field and stress-dichroism experimental results. The model is then used to study the temperature dependence of phonon-assisted tunneling rates of 60°and 90°reorientations over a wide temperature range, using a formalism that we have developed for this purpose. Special emphasis is placed on studying the role played by the quadratic defect-lattice coupling. Where possible, theoretical results are compared with experiment. © 1979 The American Physical Society.