Raman study of α-quartz-type Ge1−xSixO2 (0 < x ≤ 0.067) single crystals for piezoelectric applications

Abstract

As potential candidates for high temperature piezoelectric materials, α-quartz-type Ge_1−xSi_xO₂ (0 < x ≤ 0.067) single crystals grown by the flux method were structurally and thermally characterized. When compared to pure α-GeO₂, room temperature polarized Raman spectra contained additional lines which have been assigned from density functional theory on a α-Ge_0.833Si_0.167O₂ solid solution. The results highlight that Si–O–Ge bridges were involved. Moreover, a linear relationship between the wavenumber position of the main A₁ Raman lines and the SiO₂ substitution rate x was also observed. The analysis of the temperature dependence of unpolarized Raman signals of an α-Ge_1−xSi_xO₂ phase with x = 0.067 pointed out the high-thermal stability up to 1000 °C of the α-quartz-like structure related to the lack of a libration mode and to the absence of a softening mode with temperature.