New results on high perfection langasite crystals: studies of crystalline defects and mode shapes

Langasite (LGS: La₃Ga₅SiO₁₄) is a new piezoelectric material obtained by the Czochralski method. In this paper we present results obtained on new samples which are more representative of the crystalline quality achieved with this material. Observations using X-ray transmission topography have permitted verification of the quality of samples of different origins and to analyse the nature of their crystalline defects. Vibration modes of different types of devices made with LGS have been studied by X-ray transmission topography. This study was essentially concerned with plane or plano-convex resonators. This material has interesting properties and among them compensated cuts with a large coupling coefficient and a very reduced angular sensitivity