Growing of SixGe1-xO2 single crystals with a-quartz structure and their characterization

Crystals of alpha-SixGe1-xO2 solid solution is a new material with relatively high piezoelectric coefficients and temperature stability. Theoretical and experimental study on the development of reliable and reproducible method of alpha-SixGe1-xO2 crystal growth under hydrothermal conditions will be proposed in the report. Influence of the composition of solutions, T-P parameters, growth rates of different faces, capture and distribution of Si and Ge on morphology and internal structure of the crystals, and the basic crystallochemical characteristics and properties of the crystals have been investigated. The most important result of the performed investigations is an experimental proof of the growth of alpha-SixGe1-xO2 single crystals with alpha-quartz structure under conditions of the stable existence of trigonal quartz and tetragonal germanium oxide phases. The maximum GeO2 content (38,78 mass%) has been attained while crystal growth in aqueous solutions of ammonium fluoride at temperature of 700 degrees C and pressure of the order of 180MPa. Crystals grown in alkaline solutions at similar T-P parameters are characterized by the maximum GeO2 content of 25 mass%. A temperature of the alpha-beta polymorphous transition of alpha-SixGe1-xO2 with GeO2 content of 38 mass% has reached 840 degrees C (instead 573 degrees C of alpha-quartz). GeO2 portion increases in alpha-SixGe1-xO2 crystals at temperature and growth rates rise. The highest GeO2 content belongs to the growth sectors of positive and negative rhombohedra; the minimum - belongs to the growth sectors of hexagonal prism. A regular rise of the unit cell parameters and refraction indices are observed at GeO2 portion increase in alpha-SixGe1-xO2 crystals. An appearance of new absorption bands was found in IR-spectra, caused by a formation of Si-O-Ge bridge bonds. A shifting of practically all bands in the IR-spectra of the combinational scattering for a distance of 10-15 cm(-1) into the region of short-wave vibrations seems to be related to this very fact. The basic piezoelectric constants d(11) and d(14) alpha-SixGe1-xO2 crystals have increased as compared to quartz by approximately two times.