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Using the slow-cooling method in selected fluxes, we have grown spontaneously nucleated single-crystals of pure GeO(2) and SiO(2)-substituted GeO(2) materials with the α-quartz structure. These piezoelectric materials were obtained in millimeter size as well-faceted, visually colorless, and transparent crystals. Cubic-like or hexagonal prism-like morphology was identified depending on the chemical composition of the single-crystals and on the nature of the flux. Both the silicon substitution rate and the homogeneity of its distribution were estimated by Energy Dispersive X-ray spectroscopy. The cell parameters of the flux-grown GeO(2) and Ge(1-x)Si(x)O(2) (0.038 ≤ x ≤ 0.089) solid-solution were deduced from their X-ray powder diffraction pattern. As expected, the cell volumes decrease as the silicon content substitution increases. A room temperature Infrared spectroscopy study confirms the absence of hydroxyl groups in the as-grown crystals. Unlike what was observed for hydrothermally grown GeO(2) crystals, these flux-grown oxide materials did not present any phase transition before melting as pointed out by a Differential Scanning Calorimetry study. Neither a α-quartz/β-quartz transition as encountered in SiO(2) near 573 °C nor a α-quartz to rutile transformation were detected for these GeO(2) and Ge(1-x)Si(x)O(2) single-crystals.

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A mixed glass former effect has been observed in the glassy system 0.3Li 2 S-0.7[(1-x)-SiS 2 -xGeS 2 ], where 0 e x e 1. It corresponds to a large enhancement of ionic conductivity for compositions 0.50 e x e 0.64. The variations of the electrical characteristics are closely related to those of the glass transition temperature and the density. Structural investigations by Raman and SAXS techniques have been carried out on this system. The results indicate that the high conducting glasses belonging to the central composition region, i.e., 0.50 e x e 0.64, are phase separated, forming entities with a composition close to GeS 2 which are embedded in a matrix close to Li 2 SiS 3 , while glasses from the limiting composition ranges, i.e., 0 e x < 0.50 and 0.64 < x e 1, are homogeneous.

The spontaneous nucleation by the high-temperature flux method of GeO 2 and SiO 2 -substituted GeO 2 (Ge 1Àx Si x O 2 ) compounds was improved to give single crystals free of hydroxy groups. The crystal structure and quality of these -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 1Àx 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 -quartz-type GeO 2 structure was followed by the evolution of the intra-tetrahedral angle and other structural parameters. The TO 4 (T = Si, Ge) distortion was found to be larger in -GeO 2 than in -SiO 2 and, as expected, the irregularity of the TO 4 tetrahedra decreased linearly as the substitution of Si for Ge increased. † The record of GeO 2 data was optimized according to its Laue class (3m), which gave a higher number of unique reflections.

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