Melilite-type silicate single crystals for high-temperature piezoelectric applications

Abstract

Melilite-type silicate single crystals have emerged as promising materials for high-temperature piezoelectric applications in devices such as accelerometers, gas sensors, gas injectors, and pressure sensors. Sr-substituted Ca₂MgSi₂O₇ (Sr-CMS) single crystals were grown using the Czochralski (Cz) method. The Sr-CMS crystals exhibited no phase transition from room temperature to the melting temperature, with a piezoelectric d′₃₁ constant of 2.1 pC/N and a compressive strength of 830 MPa on a (ZXt)45° rotation-cut crystal substrate. Thus, Sr-CMS single crystals are promising for high-temperature pressure sensors. Ca₂Al₂SiO₇ (CAS) single crystals, which can also be grown using the Cz method, were investigated for high-temperature microbalance (MB) applications. They exhibit stable piezoelectric properties at high temperatures and have a lower density than langasite-type crystals. The thickness-shear vibration (d′₁₅ mode) of the CAS crystals was characterized, with the (XYw)45°-cut substrate showing the highest d′₁₅ constant. Using this crystal substrate, an LiZrO₃/Au/CAS device was configured and characterized as an MB. The device exhibited a resonance frequency shift when exposed to CO₂ gas in an air atmosphere at 500 °C, indicating that CAS single crystals can be used for MB applications at high temperatures.