Raman spectroscopy and high pressure study of synthetic Ga,Ge-rich tourmaline

We present Raman spectroscopic analysis of the synthetic Ga,Ge-rich tourmalines at pressures up to 30 GPa for the first time. Based on the experimental data, we obtained correlation between the Raman band positions and the cation substitutions in the tetrahedral and octahedral sites at ambient conditions. A new band of Ge-O stretching vibrations, which is not common in natural tourmalines, occurs at ~ 870 cm^-1. The main Raman bands shift to the higher frequencies with increasing pressure due to decrease in the bond lengths, associated with structural deformations. The lattice dynamic calculated spectra of tourmalines with various compositions resemble those measured experimentally. Analysis of experimental and theoretical data reveals a possible phase transition at ~ 18.4 GPa in the tourmalines with up to 10 wt% Ga₂O₃ and 9 wt% GeO₂.