A combined XAS and XRD study of the high-pressure behaviour of GaAsO₄ berlinite

¹ Laboratoire des Sciences de la Terre, École Normale Supérieure de Lyon 46, allée d'Italie 69364 Lyon Cedex 07, France
² Materials Research Group in High Pressure Synthesis, Department of Chemistry and Biochemistry, Arizona State University - Tempe, AZ 85287, USA
³ Physique des Milieux Condensés, Université Pierre et Marie Curie, B77 4, place Jussieu 75252 Paris Cedex 05, France

Received: 5 May 1997
Accepted: 20 October 1997

Abstract

Combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) ex peri ments have been carried out on α- (berlinite structure) at high pressure and room temperature. XAS measurements indicate four-fold to six-fold coordination changes for both cations. The two local coordination transformations occur at different pressure rates but appear to be coupled. A reversible transition to a high-pressure crystalline form occurs around 8 GPa. At a pressure of about 12 GPa, the system mainly consists of octahedral gallium atoms and a mixture of arsenic in four-fold and six-fold coordinations. A second transition to a highly disordered material with both cations in six-fold coordination occurs at higher pressures and is irreversible.