Phase relations of AgI under high pressure and high temperature

Using a multi-anvil high-pressure device and synchrotron radiation, X-ray in situ observations of AgI under high pressure and high temperature up to 6.0 GPa and 1000 K have been performed to investigate the phase relations between alpha-AgI, rocksalt-type, disordered rocksalt-type, and liquid phases. The melting curve of alpha-AgI has a temperature maximum at about 1.0 GPa, which suggests the existence of a dense liquid phase above this pressure. The three phases of alpha-AgI, disordered rocksalt-type, and liquid meet in a triple point in the vicinity of 823 K and 1.3 GPa. The melting curve of the disordered rocksalt phase is linear with a positive slope (dT/dP = 40 deg/GPa). The transition between the rocksalt and the disordered rocksalt phases is a broad and diffuse disordering type within the same structure. The formation of the disordered rocksalt phase has been hence estimated with the variation of a relative intensity ratio of (111) and (200) diffractions from the rocksalt phase. With increasing pressure the rocksalt phase becomes stable at higher temperature. At 6.0 GPa the rocksalt phase directly melts without the transition to the disordered rocksalt phase. (C) 2002 Elsevier Science Ltd. All rights reserved.