Relaxation in ZnSe: Cr2+ investigated with longitudinal ultrasonic waves

Abstract

Temperature dependences of phase velocity and absorption of ultrasound were investigated in ZnSe crystal doped with Cr2+ ions at the frequencies 32-158 MHz. Absorption peak and variation of phase velocity found in the temperature interval 10-20 K were interpreted as manifestation of the Jahn-Teller effect. Temperature dependences of relaxation time, relaxed, and unrelaxed moduli C= 1 2 (C11 + C12 +2 C44) were restored. The dependences were compared with the results of such investigations in ZnSe: Ni2+ and analyzed regarding lattice stability of the crystals. Fitting of the temperature dependence of the relaxation time was done with account of thermal activation over the potential barrier, quantum tunnelling with phonon emission, and two phonon process analogous to Raman scattering. Thermal activation proved to be the dominant mechanism of relaxation above 6 K and quantum tunnelling-below this temperature. © 2006 The American Physical Society.