J. Phys. IV France
Volume 126, June 2005
Page(s) 7 - 12

J. Phys. IV France 126 (2005) 7-12

DOI: 10.1051/jp4:2005126002

The main features of GaPO$_{\bf 4}$ hydrothermal crystal growth under conditions of direct and retrograde solubility

D.V. Balitsky1, V.S. Balitsky2, E. Philippot1, Ph. Papet1 and F. Pey1

1  LPMC UMR 5617 CNRS, University Montpellier II, France
2  IEM RAS, Chernogolovka, Russia

GaPO4 recrystallisation was studied under hydrothermal conditions at temperatures from 140 to 310$^{\circ}$C (autogeneous pressures from 2 to 150 bar). The acidic solvents of pH 4 to 0 at ambient conditions were used as mineralizers. The retrograde solubility of GaPO4 was observed under 260$^{\circ}$C (pressure up to 20 bar) and direct - above 280$^{\circ}$C (pressure above 50 bar). Low values of the initial solvent pH on GaPO4 solubility at temperatures up to 260$^{\circ}$C have an influence to increase GaPO4 solubility and in the same time decrease crystalline quality, for example, rise of OH content is observed. Some solvents with pH near to 4 tested as mineralizers exhibit low solubility of GaPO4, but increasing value at temperatures above 280$^{\circ}$C and lead to an attractive crystal growth. So, a possible explication of this phenomenon is a formation of few stable phases from an initial solution which can participate or no in reactions with GaPO4 at certain T-P conditions.

The study of crystalline quality and physical properties as well piezoelectric of GaPO4 single crystals have shown a significant superiority of crystals obtained at temperatures above 280$^{\circ}$C (pressures above 50 bar).

© EDP Sciences 2005