Ultrasonic investigation of the relaxation time and the dynamic, relaxed, and unrelaxed elastic moduli in ZnSe:Cr

The temperature dependence of the phase velocity and absorption of ultrasound propagating along the [110] axis in a ZnSe crystal doped with Cr2+ ions is investigated in the frequency interval 32-158 MHz. It is found that the absorption peak and anomalies of the phase velocity observed in the temperature interval 10-20 K are of a relaxation nature. The temperature dependence of the relaxation time and the relaxed (isothermal) and unrelaxed (adiabatic) elastic moduli Cl = 1 2 (C11 + C12 +2 C44) are recovered from the data. Oscillations of the amplitude and phase of the signal are observed at 32 MHz. An interpretation of this phenomenon is proposed. © 2007 American Institute of Physics