09:00 〜 09:15
[SIT25-01] High-pressure Equation of State of Schreibersite Fe2.15Ni0.85P: Implications for the Martian Core
キーワード：schreibersite, high pressure, equation of state, Martian core
Phosphorus is thought to be an important light element existing in planetary cores. The phosphorus abundance is evaluated to be ~0.20 wt% in the Earth’s core, and ~0.32 wt% in the Martian core. To fully understand its existence in planetary cores, structural and physical properties of iron-nickel phosphides should be investigated under high pressure and high temperature. (Fe,Ni)3P-schreibersite is observed as a common accessory in the veinlet of iron and stony-iron meteorites, so that it is of significance to discuss and constrain the properties of planetary cores. The equation of state of a natural single-crystal schreibersite, Fe2.15Ni0.85P, has been studied up to ~50 GPa at room temperature in a diamond anvil cell using in situ synchrotron-radiation X-ray diffraction. The sample kept its tetragonal structure (I-4 ) up to the highest pressure with no observation of phase transition. Experimental results have shown that the magnetic collapse of Fe2.15Ni0.85P is weakened because of the substitution of nickel, leading to an isotropic axial compressibility. The pressure-volume data were fitted by the third-order Birch-Murnaghan equation of state, yielding K0 = 184(4) GPa, K0' = 4.1(2), V0 = 365.9(1) Å3. The density of Fe2.15Ni0.85P, along with several iron sulfides and iron phosphides has been calculated under relative pressure-temperature conditions of the Martian core. The comparison with that of γ-Fe and a density model of the Martian core evidences that nickel and phosphorus dopant would result in density reduction of iron sulfides, suggesting that (Fe,Ni)3(S,P) might be a possible compound existing in the Martian core.