[Raman scattering spectra of Ca3NbGa3Si2O14 (CNGS) crystals]

The CNGS crystal belongs to the trigonal system, the 32 point group and the P321 space group, which is the same as the LGS crystal. Its lattice constants are a = 0.808 73 nm and c = 0.497 98 nm. The primitive cell of the CNGS crystal contains only one formula unit (23 atoms). The vibration modes were measured with Raman spectroscopy technique, assigned with ab initio molecular orbit calculation method. In order to model the crystal, two clusters Ca3NbGa2SiO12 and Ca3NbGaSi2O12 were designed, and calculations were carried out on them. Their configurations were optimized, and the vibration frequencies were calculated with UHF method. By investigating the force constants and activities of the assigned Raman spectra, the structure of CNGS crystal was analyzed, and its layer structure and piezoelectric properties were confirmed. It is concluded that CNGS crystals have more excellent anisotropy and piezoelectric properties than LGS crystals.