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 alpha(11) and alpha(33) were measured and found to be on the order of 5.70 x 10(-6)/degrees C and 10.12 x 10(-6)/degrees C, respectively. The electrical resistivities of the CAS crystal along the X- and Z-directions at 700 degrees C were found to be 3 x 10(7) and 2 x 10(8) Omega.cm, respectively. The electro-elastic constants were evaluated by using the impedance and pulse-echo methods, where the piezoelectric coefficients d(14) and d(36) were determined to be 6.7 and 2.8pC/N at room temperature, respectively. Moreover, the temperature dependence of the electroelastic 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 degrees 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 d(11)(*) (3.1 pC/N) was achieved for the (XYtZ)45 degrees/ - 55 degrees crystal cut, and the largest shear piezoelectric d(26)(*) (4.7 pC/N) was found for the (YX/)45 degrees crystal cut, nearly two times that of alpha-quartz.