High-Temperature Elastic Moduli of Flux-Grown α-GeO2 Single Crystal

From high-precision Brillouin spectroscopy measurements, six elastic constants (C-11, C-33, C-44, C-66, C-12, and C-14) of a flux-grown GeO2 single crystal with the -quartz-like structure are obtained in the 298-1273 K temperature range. High-temperature powder X-ray diffraction data is collected to determine the temperature dependence of the lattice parameters and the volume thermal expansion coefficients. The temperature dependence of the mass density, , is evaluated and used to estimate the thermal dependence of its refractive indices (ordinary and extraordinary), according to the Lorentz-Lorenz equation. The extraction of the ambient piezoelectric stress contribution, e(11), from the C-11-C-11 difference gives, for the piezoelectric strain coefficient d(11), a value of 5.7(2) pCN(-1), which is more than twice that of -quartz. As the quartz structure of -GeO2 remains stable until melting, piezoelectric activity is observed until 1273 K.