Resonance behavior of langanite and langatate plates driven by lateral field excitation

Langanite (LGN, La₃Ga₅₅Nb_0.5O₁₄), Langatate (LGT, La₃Ga₅₅Ta_0.5O₁₄) single-crystal piano-convex resonators were driven in thickness modes by lateral field excitation using a custom fixture. Resonance behavior was characterized as a function of in-plane (azimuthal) rotation angle for the thickness vibration modes of doubly rotated orientation. Specifically, S₁₁ reflection coefficients were measured for the first and third overtones of the c-mode and the b-mode using a network analyzer and converted into relative piezoelectric coupling coefficients. Results are presented in terms of relative lateral piezoelectric coupling coefficients versus azimuthal angle. Comparison with theoretical predictions, made for: the case of simple thickness modes (i.e., plane waves) using an extension of the Christoffel-Bechmann method with published materials constants, shows good agreement. Furthermore, it is demonstrated that lateral field excitation of some doubly rotated cuts of LGN and LGT offers the potential for significantly enhancing c-mode piezoelectric coupling, and for tuning out the unwanted b-mode, as compared to thickness-field excitation