Investigation of acoustoelectric phenomena in Sn2P2S6 single crystals

The ultrasonic measurements of electronic attenuation have been performed i n the crystals of ferroelectric semiconductor Sn2P2S6, which exhibit strong piezoelectric effect. From the dependence of electronic attenuation of ult rasound on conductivity the electromechanical coupling parameters have been calculated. The temperature dependence of acoustoelectric voltage has been measured and it was shown that it mainly follows the variation of electrom echanical coupling constant. The influence of the long time crystal exposur e in paraelectric phase near the phase transition temperature together with illumination of the Sn2P2S6 sample on ultrasonic velocity and attenuation has been also studied. It was shown, that relaxation of electronic subsyste m significantly changes the critical ultrasonic behaviour. In this case the temperature anomalies of ultrasonic velocity and attenuation become very s imilar to that of ferroelectric with incommensurate phase.