Dynamics in the System of Dipolar Impurity Centers in Crystals

Abstract

AbstractA model is proposed for the description of the dynamics in the system of dipolar impurities in crystals. The impurities are assumed to reorient by the Arrhenius temperature dependence in the case when the activation energy is much larger than the temperature of reorientation freezing (the temperature of the phase transition in the impurity subsystem). The reorientation is caused by the transitions between the localized (in the minima of the adiabatic potential) and excited delocalized states of the impurity induced by one‐phonon processes (the multiphonon ones are ineffective at the low temperatures under consideration). The freezing of the reorientation at each center takes place at temperatures, at which the energy gap between the effectively populated localized state and the delocalized one becomes larger than the maximum frequency of the crystalline phonons. The rise of the impurity concentration increases the phonon‐exchange interaction between the near‐neighbor centers during their reorientation, resulting in the increase of the energy of the delocalized state, and hence in the increase of the freezing temperature of the dipole dynamics. In the framework of this approach the system of Li+:KTaO3, is considered as an example.