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Physics and Chemistry of Minerals, 29, pp. 1-9, (2002) [doi: 10.1007/s002690100207]

Equation of state, elasticity and shear strength of pyrite under high pressure

S. Merkel, A.P. Jephcoat, J. Shu, H.K. Mao, P. Gillet and R.J. Hemley

Physical properties including the equation of state, elasticity, and shear strength of pyrite have been measured by a series of X-ray diffraction in diamond-anvil cells at pressures up to 50 GPa. A Birch-Murnaghan equation of state fit to the quasihydrostatic pressure-volume data obtained from laboratory X-ray source/film techniques yields a quasihydrostatic bulk modulus K_0T=133.5 (5.2) GPa and bulk modulus first pressure derivative K'_0T=5.73 (0.58). The apparent equation of state is found to be strongly dependent on the stress conditions in the sample. The stress dependency of the high-pressure properties is examined with anisotropic elasticity theory from subsequent measurements of energy-dispersive radial diffraction experiments in the diamond-anvil cell. The calculated values of K_0T depend largely upon the angle between the diffracting plane normal and the maximum stress axis. The uniaxial stress component in the sample, t=₃-₁, varies with pressure as t=-3.11 0.43P between 10 and 30 GPa. The pressure derivatives of the elastic moduli dC₁₁/dP=5.76 (0.15), dC₁₂/dP=1.41 (0.11) and dC₄₄/dP=1.92 (0.06) are obtained from the diffraction data assuming previously reported zero-pressure ultrasonic data (C₁₁=382 GPa, C₁₂=31 GPa, and C₄₄=109 GPa).

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