Pressure Determination by Raman Spectra of Water in Hydrothermal Diamond-Anvil Cell Experiments

The technique of using spectroscopic pressure gauges provides an efficient method for in-situ pressure determination in hydrothermal diamond-anvil cell (HDAC) experiments. Rhenium with a thickness of 0.33 mm was used as a gasket and the sample chamber was 0.5 mm in diameter. Pure water was loaded into the chamber of the HDAC together with a single crystal of quartz and cubic boron nitride. The experimental pressure was estimated according to the Raman shift of the 464 cm-1 peak of quartz. The sample was heated by two small furnaces made of NiFe alloy wires and the temperature was measured by a thermocouple, which was calibrated using the melting points of 1-naphthol, salicylic acid, hippuric acid and phenolphthalein at atmospheric pressure before the experiment. It was observed that the shapes of the OH stretching band of water at a certain temperature do not show variation with increasing pressure.