Lattice vibration of Sr3TaGa3Si2O14 single crystal

Based on the space group theory,the normal vibration modes of Sr3TaGa3Si2O14(STGS) single crystal were predicted,and the Raman scattering intensities of non-polar and polar modes were calculated.The Raman spectrum of STGS crystal was measured,and lattice vibration modes of STGS crystal were assigned.For symmetry species A1,six typical Raman-active optical modes have been recorded at 126,245,557,604,896 and 991 cm-1,respectively.It is easy to assign the mode of 126 cm-1 as the relative translation between SiO4,Sr and the TaO6.The mode 245 cm-1 corresponds to the twisting vibration of SiO4 correlating with the Sr—TaO6—Sr stretching vibration.The mode 557 cm-1 was assigned as the O—Ta—O stretching vibration,while the mode 604 cm-1 as the O—Ga—O stretching vibration.The band at 896 cm-1 in the Raman spectrum was assigned to be the O—Si—O stretching vibration of the two SiO4 tetrahedra in the primitive cell of STGS single crystal.Meanwhile,the band at 991 cm-1 in the Raman spectrum was assigned to be the Si—O stretching vibration of the two SiO4 tetrahedra in the primitive cell of STGS single crystal.The layer structure of STGS crystal was identified by both theory study and Raman spectroscopy experiment results.The small anisotropy and piezoelectric modulus of STGS crystal were ascribed to the weak distortion of decahedral unit.