Abstract
The pressure dependence of Raman peaks of cubic boron nitride (cBN) is determined at 100, 200 and 300C using pressure scales of ruby and gold. At pressures lower than 6 GPa, the pressure dependences of cBN Raman determined with the ruby pressure scale for transverse-optical and longitudinal-optical modes are 3.45 and 3.36 cm-1/GPa at 100C and 3.43 and 3.44 cm-1/GPa at 300 C, respectively. These values are consistent with those in a previous study conducted at room temperature using the ruby pressure scale. Synchrotron x-ray diffraction experiments using a gold pressure marker also yield 3.45 cm-1/GPa for TO mode at 200 C in a range of pressure up to 32 GPa. Under the present pressure and temperature conditions, the pressure dependence of Raman peaks of cBN seems to be independent of the temperature conditions. cBN can be used as an optical pressure marker under high temperature conditions.We also report on the Raman spectra of water under high temperature and pressure conditions and show a discontinuity in the pressure dependence of the OH stretching frequency. As pressure increases, the strength of hydrogen bonding increases rapidly in the pressure ranges up to 0.46 GPa at 25 C, 1.0 GPa at 100 C, and 1.3 GPa at 300 C and slowly above these pressures. This finding clearly demonstrates the existence of discontinuities in the pressure response of the hydrogen bonds of water, which suggests a possible structural change under these conditions.
