How to qualify LGT crystal for acoustic devices?

Before using any piezoelectric crystal to realize acoustic devices (sensors, transducers, actuators or ultra-stable resonators) and beyond its mechanical properties, the crystal material itself has to be characterized. Whether the very interesting properties of the LGT crystal make it the best candidate to substitute quartz crystal for frequency output devices, we must take into account the crystal quality. Indeed, applications require homogeneous crystals with reproducible physical properties. The presence of structural defects and inhomogeneity of the crystal composition significantly affect the physicochemical properties (optical, electrical, piezoelectric.), and can be revealed by chemical, optical, and electrical analytical methods. So, before manufacturing acoustic devices, we perform different analyses as: ESR, IR, and UV-Vis spectrometry, ICP-MS coupled with a femtosecond laser ablation, electrical resistivity. After that, we have fabricated small Bulk Acoustic Wave resonators working on a thickness shear mode of vibration to tentatively know the influence of the crystal quality on the acoustic properties.