Modulation of quartz-like GeO 2 structure by Si substitution: an X-ray diffraction study of Ge 1− x Si x O 2 (0 ≤ x < 0.2) flux-grown single crystals

The spontaneous nucleation by the high-temperature flux method of GeO 2 and SiO 2 -substituted GeO 2 (Ge 1− x Si x O 2 ) 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 Ge 1− x Si x O 2 crystals 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 GeO 2 structure was followed by the evolution of the intra-tetrahedral angle and other structural parameters. The T O 4 ( T = Si, Ge) distortion was found to be larger in α-GeO 2 than in α-SiO 2 and, as expected, the irregularity of the T O 4 tetrahedra decreased linearly as the substitution of Si for Ge increased.