High-pressure Raman spectroscopy study of α-quartz-like Si1-xGexO2 solid solution

Spontaneous α-Si1-xGexO2 single crystals were synthesized using the set of crystal growth techniques: hydrothermal (XGe = 0.09, 0.20), flux (XGe = 0.45, 0.70) and recycling (XGe = 0.96). The XRD and spectroscopic studies with non-negative matrix factorization show linear dependences of structural parameters and Raman shift on germanium content and confirmed the existence of a complete series of α-Si1-xGexO2 solid solution. The synthesized samples of the solid solution were studied by Raman spectroscopy at the ambient conditions and for the first time at high pressures up to ∼30 GPa. The obtained results suggest a phase transition “α-quartz → post-quartz” for Si1-xGexO2 in the examined pressure range. The formation of the possible intermediate phase (quartz-II) was detected for Si1-xGexO2 with XGe = 0.09, 0.20 and 0.45 at 11, 10 and 7.5 GPa, respectively. The linear dependences of the pressure value of phase transitions on germanium content were observed. At decompression, the post-quartz phase remained stable that was determined by Raman spectra for all compositions of solid solution. Obtained experimental results revealed the correlation of the chemical composition, spectroscopic characteristics, and structural deformations at ambient conditions and at high pressures.