Advances in crystal growth and characterizations of gallium orthophosphate, GaPO4

Gallium orthophosphate, GaPO4, is a piezoelectric material isostructural with alpha -quartz. SiO2, with better piezoelectric characteristics: higher coupling coefficient for its temperature compensated cut and wider thermal stability (up to 933 degreesC), A new investigation of the solubility of GaPO4 in different acids and their mixtures allows to determine the metastable zone of which the knowledge is primordial for a good growth restart. The comparison of experimental growth results obtained in horizontal glass vessels (T-c < 170 degreesC) and vertical autoclaves (T-c > 170 degreesC) leads to specify a necessary minimum value of the solute supply at the interface crystal/solution. On the other hand, natural large seeds being not available, the seed lengthening is carried out with the splicing technique followed by crossed crystal growths to decrease the density of structural defects. At the same time, characterizations of crystals have been undertaken to check: the OH content by infrared spectroscopy; the crystalline quality (specially crystals after splicing) and the growth restart by X-ray topography; the piezoelectric properties. (C) 2001 Elsevier Science B.V. All rights reserved.