Structural studies on liquids and glasses under high pressure and high temperature

After a brief review of recent studies under high-pressure and high-temperature conditions using large-volume multi-anvil presses in the SPring-8 synchrotron radiation facility, new data of the pressure dependence of the structure factor for silica glass under high pressure is presented. The position of the first sharp diffraction peak in the structure factor of silica glass moved to a higher momentum transfer as pressure is increased. It moves in the same direction as temperature is increased at 8.5 GPa. The intermediate-range structure relaxes to a denser one. On decompression at room temperature, the position of the first sharp diffraction peak showed a large hysteresis. A smaller hysteresis was observed for a sample without a heat treatment at high pressure. A mechanism of permanent densification of silica glass by the heat treatment under high pressure is discussed.