β-Ga4GeO8 Stability Under Extreme Conditions (up to 600 °C and 30 GPa)

Abstract

The Ga₄GeO₈ compound has attracted sufficient attention as an advanced optical material and host matrix material for near-infrared phosphors. A complex study (scanning electron microscopy, energy dispersive X-Ray spectroscopy, powder X-Ray diffraction, lattice dynamics calculations, and Raman spectroscopy up to 600 °C and 30 GPa) is presented on the synthetic β-Ga₄GeO₈ compound. The β-Ga₄GeO₈ crystals (up to 200 μm in size) are synthesized under hydrothermal conditions (600/650 °C, 100 MPa) at temperatures sufficiently lower than previously reported. The unit cell parameters are: a = 8.2701(2), b = 8.2392(2), c = 9.0886(2) Å, β = 117.674(1)°, V = 548.45(2) ų, space group P2₁/c. The obtained structural data are used for the lattice dynamics calculations. The assignment of A_g and B_g bands (cm⁻¹) in calculated and experimental non-polarized Raman spectra at the ambient conditions is carried out. No significant changes are observed in the Raman spectra up to ≈600 °C. In situ Raman spectroscopy indicates that the structural integrity of the material is well preserved up to ≈11 GPa. Thus, β-Ga₄GeO₈ is stable at least up to ≈600 °C and ≈11 GPa, which may indicate its potential applications under extreme conditions.