Synchrotron X-ray powder diffraction study of natural P2-omphacites at high-pressure conditions

摘要

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-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~(-1), respectively. The third-order Birch-Murnaghan equation of state was used to interpolate the experimental P - V data, obtaining K_0 = 116.6(±2.5) GPa and K'_0 = 6.03(±0.60). K_0 was 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 K_0 are discussed in the light of a comparison between techniques to determine the bulk modulus of crystalline materials from static compression diffraction data.