Development of the Next Generation Megabar High-Pressure Cells: A COMPRES Grand Challenge

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

0135626 Hemley We propose to develop the next generation static ultrahigh-pressure apparatus that will allow an increase in sample volumes in excess of 100 times those currently available in conventional diamond cells at megabar pressures. This will enable myriad mainstream analytical techniques currently unavailable for ultrahigh-pressure research, including those required for the successful utilization of major neutron and synchrotron radiation facilities that are coming on line. The new class of high-pressure cells will also improve measurement accuracy for existing in situ probe techniques, provide well-calibrated hydrostatic pressures and uniform temperatures, allow higher and more uniform temperatures to be achieved with laser heating, and provide robust and user-friendly operation. These capabilities are required to address numerous current problems in high-pressure geochemistry, geophysics, and planetary science; as such, the proposed advances are expected to have major impact in each of these areas. The increases in sample volume for the new cells will result from a combination of improvements that include enlarged anvils, modified culet shapes, designed gaskets, and added binding support for the anvils. Single-crystal diamonds synthesized at high pressures and temperatures will be enlarged by homoepitaxial chemical vapor deposition overgrowth of single-crystal diamond films to create anvils reaching 25 carats and above. Synthetic moissanite (SiC) anvils will be used for testing and for 100-fold volume increases at pressures up to 50 GPa. The larger sample chamber, in turn, will remove restrictions currently imposed by microscopic volumes and greatly improve the pressure-temperature conditions and probing capabilities at ultrahigh pressures. New presses will be built to provide the loads necessary for the larger volumes. The project will be carried out in coordination with the newly formed COnsortium for Materials Properties Research in the Earth Sciences (COMPRES), through which the new high-pressure capabilities will be made available to the high-pressure geoscience community. ***