Evaluation of Acoustic Properties for Ca₃Nb(Ga_0.75Al_0.25)₃Si₂O₁₄ Single Crystal Using the Ultrasonic Microspectroscopy System

Acoustically related physical constants were experimentally determined for Ca₃Nb(Ga_0.75Al_0.25)₃Si₂O₁₄ (CNGAS) single crystal for the first time. Several plate specimens of the X-, Y-, Z-, 40.24° Y-, and 144.98° Y-cut were prepared from a CNGAS single crystal ingot grown by Czochralski technique. Elastic constants, piezoelectric constants, and their temperature coefficients for CNGAS were determined from longitudinal wave and shear wave velocities at around room temperature, measured by the ultrasonic microspectroscopy system. Dielectric constants, density, and coefficients of thermal expansion were also measured. It was demonstrated that the determined constants could provide calculation accuracy within ±0.12% in leaky surface acoustic wave velocity. The piezoelectric constants for CNGAS were a 7.2% increase in e₁₁ and a 1.7% decrease in e₁₄ due to Al-substitution effect, compared with those of Ca₃NbGa₃Si₂O₁₄. The appropriate cut angle for thickness-shear mode resonator with zero temperature coefficient of velocity was estimated to be around 150° Y-cut from calculations using the determined constants of CNGAS exhibiting electromechanical coupling factor k² of 3.19% and power flow angle of -1.70°.