Investigation of CuInP2S6 family lyered crystals for ultrasonic transducers

Investigation results of piezoelectric and dielectric (20 Hz - 1 MHz) properties of layered CuInP₂S₆ crystals with different compositions and stoichiometry are presented. It was shown that largest phase transition temperature T_c ap 330K was observed for indium rich CuInP₂S₆ crystals. In these CuIn_1+deltaP₂S₆ crystals at room temperature electromechanical coupling constant comparable to that of pure CuInP₂S₆ could be obtained after appropriate poling. Critical dielectric anomalies are found at the phase transitions. It was shown that above phase transition the dielectric properties are strongly influenced by high electrical conductivity. The DC conductivity and conductivity relaxation time exhibits an anomaly close to the phase transition temperature T_c=330 K. Its activation energy exhibit only a weak change close to the ferrielectric phase transition temperature in investigated crystals.