Abstract
Millimeter-sized crystals of formula Ge 1−x Si x O 2, i.e. GeO 2 materials partially substituted by SiO 2 , were obtained for the first time both in the middle and the Si-rich parts of the GeO 2-SiO 2 composition domain (0.5 ≤ x ≤ 0.93) by spontaneous nucleation using the hightemperature flux method. The X-ray crystal diffraction (XRD) data at room temperature confirm the non-centrosymmetric α-quartz-type structure and the low level of defects for these as-grown materials. The silicon content in the Ge 1−x Si x O 2 crystals was determined by interpolation from the inter-tetrahedral bridging angle. The complete mutual solubility is confirmed between α-SiO 2 and α-GeO 2. The deviation from the regularity of the TO 4 tetrahedra (T = Si, Ge) decreases linearly when Ge is gradually replaced by Si.