Based on the space group theory, the normal vibration modes of La 3 Ga 5 SiO 14 (LGS) crystal were predicted, and the Raman scattering intensities of non-polar and polar modes were calculated respectively. The lattice vibration and structure of LGS crystal were investigated by Raman spectroscopy and densityfunctional theory (DFT). The DFT calculations were made on SiO 4 , GaO 4 , GaO 6 , La 3 Ga 4 O 12 and La 3 Ga 3 SiO 12 clusters, which model the atomic cluster in LGS crystal. Excellent agreement has been achieved between vibrational frequencies predicted by the theory and those observed in experiments. The layer structure of LGS crystal is identified, and its excellent piezoelectric properties are mainly attributed to the large polarizability anisotropy of La 3 Ga 4 O 12 and La 3 Ga 3 SiO 12 clusters, which results from the strong interaction between Ga(Si)O 4 tetrahedras of LGS crystal.
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