The gem anvil cell: high-pressure behaviour of diamond and related materials

Abstract

The moissanite anvil cell has been used to study the high-pressure behaviour ofdiamond. The first-order Raman shift of diamond shows a strong dependence onhydrostaticity, with very different pressure dependences observed underhydrostatic and non-hydrostatic conditions. The shift of the second-order Ramanband under hydrostatic pressures was determined for the first time. Sapphirehas almost no peaks above 1000 cm−1 in the Raman spectrum and noabsorption in the ultraviolet range; it is therefore especially useful forstudies in those spectral regions. A sapphire anvil cell was used in a studyof graphite up to 24 GPa. A phase transition was found near 18 GPa,consistent with previous reports, and no peaks characteristic of diamond in the1330 cm−1 range were found, indicating that the phase is not diamond.