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

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.