Raman scattering spectra of La₃Ga₅SiO₁₄ (LGS) crystals

Abstract

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.

Raman scattering spectra of Ca3NbGa3Si2O14 (CNGS) crystals

“…The irreducible representation E denotes the two-dimensional symmetry species corresponding to 44 vibrational modes, which are Raman and IR active optical phonon modes. It can be seen that there are no more than 54 theoretically observable Raman peaks and 34 IR reflection bands, which is the same as the LGS crystal [3].…”

“…[3]. In addition, the force constants for Si(Ga)-O stretching vibrations and O -Si(Ga) -O bending or stretching vibrations are very large, which indicates that the interaction within the SiO 4 and GaO 4 tetrahedra is relatively strong.…”

“…The properties of LGS crystals have been reported in many articles [3][4][5][6][7]. Compared with the LGS crystal, the CNGS crystal was found to have shorter cut-off wavelength, slightly higher transmittance, superior piezoelectric properties and lower melting temperature [1,2].…”

Lattice vibration of Sr3TaGa3Si2O14 single crystal

“…While E denotes the two-dimensional symmetry species and it corresponds to 44 optical phonon modes with both Raman and Infrared activities. Therefore, there exist no more than 54 Raman peaks and 34 Infrared reflection bands, which is same as La 3 Ga 5 SiO 14 crystal [7]. The Raman scattering tensors concerned are as follows [22]:…”

“…In the past twenty years, the piezoelectric crystals with Ca 3 Ga 2 Ge 4 O 14 (CGG) structure have attracted a considerable amount of attention [1,2]. However, despite the large body of work on Gallate crystals such as La 3 Ga 5 SiO 14 (LGS), La 3 Nb 0.5 Ga 5.5 O 14 (LNG) and La 3 Ta 0.5 Ga 5.5 O 14 (LTG) [3][4][5][6][7], they have a major disadvantage: their structures are disordered [8]. This disadvantage was noticeable when they were investigated as piezoelectric crystals.…”