Large SiO2-substituted GeO2 single-crystals with the α-quartz structure

Colorless, transparent SiO2-substituted GeO2 single-crystals with the α-quartz-like structure have been grown by spontaneous nucleation using the slow-cooling method from K2O-3MoO3 flux. The cell parameter values as well as the semi-quantitative chemical analyses confirm the presence of Si-content in the as-grown crystals. Their thermal behavior was studied by means of differential scanning calorimetry and high-temperature X-ray diffraction. The high stability of the α-quartz-like structure as a function of temperature was confirmed up to 1000 °C. The structural parameter data have been used to estimate the lattice and volume thermal expansion coefficients from room temperature up to 1000 °C.