Thermoexcited dipole glasslike phase in the crystals with Jahn-Teller ions

Abstract

The rare-earth ions in crystals have as a rule some low laying excited energy levels. Properties of the ion on the ground or excited states are generally different, so the temperature variations of excited states population can change polarization properties of crystals remarkably. Such effect should be particularly important in the case of the crystals with Jahn-Teller ions, because of the strong coupling between the electron state and the ligand distortion for these ions. In this connection Eu⁺³ containing compounds are of the most interest. The ground state of Eu⁺³ ions is nondegenerate (⁷F₀), but the lowest excited one in the contrary is degenerate (⁷F₁). The energy splitting of ⁷F₀−⁷F₁ states is 300 cm⁻¹. Therefore, for such crystals the changes of properties caused by temperature-induced variation of population of excited (⁷F₁) state, may be strong. Besides, such changes have to be observed over the convenient temperature range.