Equation of state of {gamma}-tricalcium phosphate, {gamma}-Ca3(PO4)2, to lower mantle pressures

摘要

The -tricalcium phosphate phase (-TCP), -Ca₃(PO₄)₂, is a high-pressure polymorph of tricalcium phosphate with a potential important implication as the reservoir of rare-earth elements and very large lithophile elements in the deep mantle. In situ synchrotron X-ray diffraction measurements of the -TCP phase have been carried out using a diamond-anvil cell to 40.29 GPa at room temperature, with a methanol-ethanol mixture as the pressure medium. The pressures in the measurements have been determined by using gold metal as the internal pressure calibrant. The third-order Birch-Murnaghan equation of state fitted to the experimentally defined unit-cell parameters suggests for the -TCP phase a density of ₀ = 3.461(1) g/cm3, an isothermal bulk modulus of K_T = 100.2(13) GPa, and first pressure derivative of K'_T = 5.48(16). When K'_T is fixed at 4, the derived K_T is 113.1(12) GPa.