Generation of static pressures above 2.5 megabars in a diamond-anvil pressure cell

Abstract

A static pressure of 2.75 Mbars has been generated in a diamond-anvil pressure cell. This pressure is 1 Mbar higher than the highest static pressure previously produced in a laboratory, 1.72 Mbar by Mao and Bell [Science 200, 1145 (1978)]. Improvements in the geometry of the cut of beveled anvil surfaces, selection of diamond anvils for a high concentration of nitrogen platelets, and modifications in the design of the supporting cell for the diamond anvils resulted in the attainment of 2.75 Mbars. Pressures from 1 bar to 1.85 Mbar were measured by the ruby fluorescence method. The ruby fluorescence, however, was found to diminish in intensity with increasing pressure and to become undetectable at 1.85 Mbar. Pressures above 1.85 Mbar were calculated on the assumption of elastic behavior for the diamond anvils in two ways: (1) by extrapolation of the relationship between central pressure and force applied to the anvils, and (2) by extrapolation of radial pressure profiles. Three lines of evidence confirm that the diamond anvils behaved elastically, rather than deforming plastically, to the highest pressure achieved. The design improvements reported in this paper should result in the acquisition of a wide range of data in diamond cells at pressures above 1 Mbar, pressures at which virtually no static data have been obtained. Pressures substantially above 2.75 Mbars are probably attainable with the present design of the diamond-cell apparatus.