A comparison of volume compressions of silver and gold up to 150 GPa

Samples of silver and gold have been compressed together in a diamond anvil cell up to similar to150 GPa and the x-ray diffraction patterns recorded using a synchrotron radiation source. The parameters alphat for silver and gold, where alpha is a factor that determines the relative weights of iso-stress and iso-strain conditions and t is the difference between the axial and radial stress components, are estimated from the analysis of the diffraction data. The alphat-values are small and increase with pressure reaching 2 GPa and 0.5 GPa at 150 GPa for silver and gold, respectively. The effects of varying alpha between 1 and 0.5 on the hydrostatic volume compression derived from the measured data and the pressures computed therefrom are discussed. The compression data for silver and gold, corrected for nonhydrostatic compression effects assuming iso-stress condition (alpha=1), fit the relation (V/V-0)(Ag)=1.5946(V/V-0)(Au)(3)-3.0024(V/V-0)(Au)(2)+2.8285(V/V-0)(Au)-0.4207. The pressures computed from (V/V-0)(Ag) and (V/V-0)(Au) using equations of state from different sources have been compared. A fit of the Vinet equation to (V/V-0)(Ag) data and pressures derived from the (V/V-0)(Au) data using a recently proposed equation of state gives 5.47(2) for the pressure derivative of bulk modulus if the bulk modulus is constrained at 98.0 GPa, a value obtained from the ultrasonic measurements. (C) 2004 American Institute of Physics.