Single crystal growth and temperature dependent behaviors of melilite type piezoelectric crystal Ca2Al2SiO7

High temperature piezoelectric crystals are desired for sensing at elevated temperatures. In this work, a large size (2 in.) and low cost Ca2Al2SiO7 (CAS) crystal was grown by using the Czochralski pulling method. Thermal expansion coefficients α11 and α33 were measured and found to be on the order of 5.70 × 10−6/°C and 10.12 × 10−6/°C, respectively. The electrical resistivities of the CAS crystal along the X- and Z-directions at 700 °C were found to be 3 × 107 and 2 × 108 Ω·cm, respectively. The electro-elastic constants were evaluated by using the impedance and pulse-echo methods, where the piezoelectric coefficients d14 and d36 were determined to be 6.7 and 2.8 pC/N at room temperature, respectively. Moreover, the temperature dependence of the electro-elastic properties of the CAS crystal was investigated. The variation of elastic compliances was found to be <6% over the tested temperature range of 20-700 °C. The optimum crystal cuts with the maximum longitudinal and thickness shear piezoelectric coefficients for the CAS crystal were predicted, where the largest longitudinal piezoelectric d11∗ (3.1 pC/N) was achieved for the (XYtl)45°/−55° crystal cut, and the largest shear piezoelectric d26∗ (4.7 pC/N) was found for the (YXl)45° crystal cut, nearly two times that of α-quartz.