Abstract
The crystals of ferroelectric-semiconductor Sn2P2S6 exhibit a strong piezoelectric effect. We present measurements of ultrasonic and piezoelectric properties of other crystals of the Sn2P2S6 family: i.e., Sn2P2Se6 and CuInP2S6. The acoustoelectric method was applied to measure electromechanical coupling parameters in the ferroelectric phase of Sn2P2Se6 single crystals. The electromechanical coupling coefficients in lamellar CuInP2S6 crystalline plates were measured by the resonance method. The CuInP2S6 plate was employed as a piezoelectric transducer. The signal detected by this transducer was measured as a function of temperature and it was shown that the piezoelectric coupling disappears in the paraelectric phase. Anomalies at the phase transition have been observed at ultrasonic investigations of CuInP2S6 crystals.