Growth and piezoelectric characterisation of GeO₂single crystals with quartz structure

Abstract

The first results for growth of germanium dioxide single crystals with the crquartz type structure (a-GeOz) from refluxed hydrothermal solutions are reported. "he success of this method is due to the existence of metastable a-GeOz in aqueous solutions at relatively low temperature and to the structural similarity between a-GeO2 and a-SiOz. The continuous partial evaporation of the heated solvent, vapour condensation, saturation of the condensate by nutrient a-GeOz and growth of a-GeOz single crystals on quartz seeds are considered as the successive stages of the process. Mzre homogeneous crystals of a-GeO2 were obtained on seeds parallel to {OOOl}, (1120) and (1121) faces using sodium hydroxide and ammonium fluoride solutions in the range of temperature 90-130°C and at pressure equivalent to the fugacity of saturated vapor.Piezoelectric, elastic and dielectric properties of the mentioned above crystals for the 6rst time were studied.

Morphology controls of GeO2 particles precipitated by a facile acid-induced decomposition of germanate ions in aqueous medium

“…Crystalline GeO 2 has mainly two crystal structures; one is hexagonal with a structure of low-quartz and the other is tetragonal with a structure of rutile [2,[21][22][23][24][25]. Hexagonal GeO 2 is somewhat soluble in water (0.453 g per 100 g of water, 25 1C), while tetragonal GeO 2 is insoluble.…”

A Neutron Diffraction Study of the Thermal Stability of the α-Quartz-Type Structure in Germanium Dioxide

“…This polymorph is metastable under ambient conditions and can be obtained by cooling from above 1310 K and from direct synthesis from various precursors, such as by the hydrolysis of GeCl 4 (8). Crystal growth of this metastable form is currently an important subject of investigation and the preparation of large, single crystals is difficult (9). Up to the present, the structural stability of this form at high temperature has only been studied by Xray powder diffraction (3); however, the low relative X-ray scattering factor of oxygen with respect to germanium severely limits the precision of such measurements.…”

Ab initio study of the high‐temperature phase transition in crystalline GeO2

“…Both crystal structures have been visualized in Figure . The quartz‐type polymorph is metastable at room temperature but can be directly synthesized, nonetheless; it is also readily commercially available. The phase stability of q‐GeO 2 has been probed by several experiments: for example, by powder neutron diffraction over different ranges of pressure and temperature, respectively.…”