Contribution to the electromechanical and nonlinear properties of GaPO4 crystals

In the last decade much attention is given to piezoelectric crystals with a large value of the electromechanical coupling coefficient. Namely, quartz homeotype crystals such as berlinite, langasite and also gallium ortophosphate (GaPO₄) are the representatives of this group of crystals. Approximately two times greater coupling coefficient k₂₆ connected with the resonators vibrating in the thickness-shear mode allows extend the distance between the series and parallel resonance frequency of the resonators suitable for the frequency range from 1 to 100 MHz. This is important for some types of crystal oscillator and monolithic filter. The large electromechanical coupling coefficient increases also the difference of the resonant frequency temperature dependence of the fundamental and harmonic resonance frequencies of the resonators vibrating in the thickness-shear mode. The results of the measured resonance frequency temperature characteristics of fundamental and third harmonic of Y-cuts of GaPO₄ resonators vibrating in thickness-shear mode are presented. The computed electromechanical coupling coefficient k₂₆ are compared with the measured ones. Attention is further given to the measurement of some nonlinear properties of the rotated Y-cuts GaPO₄ resonators vibrating in essentially thickness-shear mode. The knowledge of the nonlinear interactions is important for the analysis of intermodulation phenomena resonators. This phenomena is important for the application of GaPO₄ resonators in crystal oscillators, filters and other electronic devices