SYNCHROTRON X-RAY POWDER DIFFRACTION STUDY OF NATURAL P2 /N-OMPHACITES AT HIGH-PRESSURE CONDITIONS

Abstract

Synchrotron X-ray powder diffraction experiments at high pressure conditions (0.0001-13 GPa) were performed at ESRF (Grenoble-F), on the beamline ID9, to investigate the bulk elastic properties of natural P2/n-omphacites, with quasi-ideal composition. The monoclinic cell parameters a, b, c and β were determined as a function of pressure, and their compressibility coefficients are 0.00277(7), 0.00313(8), 0.00292(5) and 0.00116(4) GPa-1espectively. The third-order Birch-Murnaghan equation of state was used to interpolate the experimental P-V data, obtaining K06.6(±2.5) GPa and K'003(±0.60). K0s also determined by means of the axial and angular compressibilities [122.5(±1.7) GPa], and of the finite Lagrangian strain theory [121.5(±1.0) GPa]. The discrepancies on K0e discussed in the light of a comparison between techniques to determine the bulk modulus of crystalline materials from static compression diffraction data.