Showing papers by "Peter M. Bell published in 1985"

Measurement of stress in diamond anvils with micro-Raman spectroscopy

Abstract: Micro-Raman spectroscopy has been used to measure first-order Raman spectra from selected volumes in diamonds under pressure in a high-pressure diamond-anvil cell in both the 180° and 135° scattering geometries. The high-frequency component of the diamond line at the diamond-sample interface is found to shift linearly with pressure and exhibits a pressure coefficient of 0.237 cm−1 kbar−1. This shift of the diamond line could be used for pressure determination. The Raman spectra from selected volumes of the diamond anvil at various depths provide useful information about stress distribution in the anvil.

Ultrahigh pressures: Optical observations and Raman measurements of hydrogen and deuterium to 1.47 Mbar.

Abstract: Hydrogen and deuterium have been pressurized under static conditions to 1.47 Mbar, which is higher by a factor of 2 than the static data of Sharma et al. (1980). Measurements of the vibron indicate an initial increase and then a sharp decrease in frequency at pressures above 0.5 Mbar. At 1.14 Mbar the vibron frequency decreased to the zero-pressure value, and at 1.47 Mbar the frequency of the vibron in hydrogen is 90/cm below the value of the vibrational mode of the isolated molecule. This pronounced softening of the vibron suggests strengthened intermolecular interaction.

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.