Characterization of CuInP2S6 family two dimensional crystals for ultrasonic transducers

The eliminating lead-based materials in ultrasonic transducers now is gaining momentum resulting in a search to replace lead-based compounds with environmental-friendly alternatives. A promising family for this type of ultrasonic applications is the family of lamellar CuInP₂S₆ crystals. We present the results of ultrasonic and piezoelectric investigations of CuInP₂S₆ crystals grown with different stoichiometry and composition. It was shown that surplus of indium in CuInP₂S₆ compound results in increase of the ferroelectric phase transition temperature to T_c = 330 K. After substitution of In by Ag the transition temperature shifts down below room temperature. But in this case at room temperature the piezoelectricity could be induced by bias DC electric field due to electrostriction. At room temperature comparatively large electromechanical coupling constants of order 30-50% were obtained in polarized indium-rich CuInP₂S₆ crystals and Ag_xCu_1-xInP₂S₆ crystals in DC bias field applied along c-axis.