Raman spectroscopy and high pressure study of hydrothermally synthesized NaGaGe₂O₆ compound with pyroxene structure

Spontaneous crystals of the synthetic analogue of clinopyroxene (space group C2/c) with the chemical formula NaGaGe₂O₆ were synthesized in hydrothermal conditions at a temperature of 600 °C and pressure of 100 MPa. We report the first experimental Raman spectrum for NaGaGe₂O₆ compound and assign its bands to specific vibrational modes. The lattice dynamic calculated spectra of this compound resemble the spectra measured experimentally. A comparative analysis of the experimental spectrum of NaGaGe₂O₆ and the spectra of natural jadeite and aegirine revealed a general similarity in topology, but with a significant shift toward lower wavenumber. Based on a comparison with natural compounds aegirine and jadeite, correlation was established between the Raman band positions and cation substitutions in the tetrahedral and octahedral sites at ambient conditions. In situ Raman spectroscopic analysis of NaGaGe₂O₆ at pressures up to 26 GPa is presented. With increasing pressure, some structural deformations occur, as evidenced by the disappearance of some bands, the appearance of new ones, and the merging of Raman bands. Analysis of experimental data shows possible structural modifications at pressures ∼1.6, ∼6, between 14 and 15 GPa and at 22 GPa.