High precision powder x-ray diffraction measurements at high pressures

Abstract

We describe a new technique for averaging two-dimensional powder diffraction patterns to form a single profile of the diffracted intensity at different values of the scattering angle 2θ, I(2θ). This approach significantly improves the precision with which d spacings and diffracted intensity can be measured relative to conventional techniques of powder diffraction at high pressures. By analyzing the diffraction patterns from samples inside the high-pressure diamond cell we find that scattering angles, 2θ, can be determined with an uncertainty of ±0.0068° and the relative intensities of different (hkl) diffraction lines are obtained to within ±0.9%. Combining the measurements of 2θ and intensity we have determined the equation of state and the Debye-Waller (B) factor of gold to 15.4 GPa. These are the highest pressures to which B has been measured to date, and we find that the results are in good agreement with thermodynamic measurements at low pressures.