Growth and Characterization of Ca₂Al₂SiO₇ Piezoelectric Single Crystals for High-Temperature Sensor Applications

The electrical properties of a piezoelectric single crystal of calcium aluminate silicate Ca₂Al₂SiO₇ (CAS) were studied at elevated temperatures and its applicability to high-temperature pressure sensors was investigated. The CAS bulk single crystal was grown by the Czochralski method. The piezoelectric d₁₄ and d₃₆ constants were respectively evaluated as 6.04 and 4.04 pC/N by the resonance and antiresonance method. The temperature dependence of the piezoelectric constant was investigated at temperatures up to 500 °C. The electrical resistivity at 800 °C was on the order of 10⁸ Ω·cm along both the crystallographic a- and c-axes. The measurement of direct piezoelectric response at 700 °C demonstrated that the CAS crystal could detect a pseudo-combustion pressure change of an automobile engine. Our observations suggest that CAS crystals are superior candidates for sensing pressure at high temperatures.