A <sub> 3 </ Sub> The Bc <sub> 3 </ Sub> D <sub> 2 </ Sub> O <sub> 14 </ Sub> Crystal Performance And Application Of Research

Since langasite (La₃Ga₅SiO₁₄, LGS) crystal was first reported in 1980s, the study on LGS has been constantly paid attention to by researchers. Study shows that LGS crystal is a kind of good piezoelectric material,electro-optic material and surface acoustic wave (SAW) material. But high price of raw material Ga₂O₃ and difficult growth of high quality crystal due to disordered structure effect commercialization of LGS crystal. Therefore, there appeared an upsurge of studying isomorphs of LGS crystal in the last decade of the 20th century.CNGS (Ca₃NbGa₃Si₂O₁₄),CTGS(Ca₃TaGa₃Si₂O₁₄),SNGS(Sr₃NbGa₃Si₂O₁₄) and STGS(Sr₃TaGa₃Si₂O₁₄) are four new piezoelectric crystals which are isomophs of LGS crystal with the general formula of A₃BC₃D₂O₁₄. As the component of Ga³⁺ in the molecular is low, the cost can be reduced by 30-40%. And owning to their ordered structures, they have better piezoelectric properties compared with LGS. In this dissertation, the properties of these four crystals are studied by several optical techniques, which may provide some theoretical guidance for study on their applications. The main contents of this dissertation are as follows:(1) The structures of four crystals were determined by X-ray powder diffraction method; thermal properties such as specific heat and thermal expansion coefficients were studied.(2) The refractive indices of SNGS in visible light region were measured without impairment by the reflection ellipsometry method. The refractive dispersion curve of SNGS was fitted to Sellmeier's equation.(3) According to interfering theory of parallel polarized light, the birefringence of SNGS was calculated through recording the interfering spectrum.(4) The optical activities of four crystals were investigated by the parallel interferometric method. The specific rotation dispersions were fitted to Boltzmann's equation, and Boltzmann's coefficients were calculated.(5) Propagating characteristics of bulk acoustic wave (BAW) in CNGS crystal were studied. The slowness curves in xy, xz and yz planes for CNGS were plotted, and acoustic velocities along x-axis, y-axis and z-axis were calculated.(6) Anisotropic acousto-optic diffraction geometry of CNGS crystal was studied by the aid of tangent condition; non-collinear acousto-optic tunable filter of SNGS crystal...