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

Physical properties including the equation of state, elasticity, and shear strength of pyrite have been measured by a series of X-ray diffraction in diamondanvil 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 yieilds a quasihydrostatic bulk modulus K_OT = 133.5 (±5.2) GPa and bulk modulus first pressure derivative K'_OT = 5.73 (±0.58). The apparrent 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_OT depend largely upon the angle Ψ between the diffracting plane normal and the maximum stress axis. The uniaxial stress component in the sample, t = σ₃ - σ₁, 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 zeropressure ultrasonic data (C₁₁ = 382 GPa, C₁₂ = 31 GPa, and C₄₄ = 109 GPa).