Modulation of quartz-like GeO2structure by Si substitution: an X-ray diffraction study of Ge1−xSixO2(0 ≤x< 0.2) flux-grown single crystals

The spontaneous nucleation by the high-temperature flux method of GeO2and SiO2-substituted GeO2(Ge1−xSixO2) compounds was improved to give single crystals free of hydroxy groups. The crystal structure and quality of these α-quartz-like piezoelectric materials were studied by single-crystal X-ray diffraction at room temperature. The refinements gave excellent final reliability factors, which are an indication of single crystals with a low level of defects. A good correlation was found between the silicon content in Ge1−xSixO2crystals determined through extrapolation from the inter-tetrahedral bridging angle and that found from energy-dispersive X-ray spectroscopy. The effect of germanium replacement by silicon on the distortion of the α-quartz-type GeO2structure was followed by the evolution of the intra-tetrahedral angle and other structural parameters. TheTO4(T= Si, Ge) distortion was found to be larger in α-GeO2than in α-SiO2and, as expected, the irregularity of theTO4tetrahedra decreased linearly as the substitution of Si for Ge increased.