10:45 〜 12:15
[SIT18-P04] Studies of the P-V-T equations of state of Fe2P and the P-T conditions of the “C22 to C23” phase transition
キーワード：Iron phosphides, Fe2P, High pressure, Planetary core
Iron-nickel phosphides, such as schreibersite [(Fe,Ni)3P], barringerite [(Fe,Ni)2P], allabogdanite [(Fe,Ni)2P], and perryite [(Fe,Ni)8(Si,P)3], are often observed as common accessories in iron and stony-iron meteorites [1][2]. These phases have been suggested formed in the solar nebulae [3], but there is a strong argument that they might also have experienced later alterations, in the parent bodies or after delivery to the Earth [4]. Recently, (Fe,Ni)2(S,Si,P) has been suggested to be a possible constituent of the metallic planetary cores [5]. Knowledge of the thermodynamic properties and pressure-temperature phase relationships of Fe2P phases therefore minerals are essential for constraints on the chemistry and physics of one of the most pristine environments in the Universe and can provide insights for the current state and evolution of the planetary core. Despite the significance, the study of such an issue is not adequate. Fe2P has been observed to transform from barringerite (P-62m, C22) into allabogdanite (Pnma, C23) at 8 GPa and 1400 K, and the latter could be quenched to ambient conditions as a metastable phase [6]. However, the phase boundary of the C22 and C23 phases has not been well studied and the insufficiency of structure and pressure-volume correlation for the Fe2P phases limits the ability to fully characterize the Fe-P system at high pressure and temperature.
In this study, the phase boundary between C22 and C23 phases has been confirmed up to 17 GPa using the multi-anvil high-pressure experimental technique at beamline BL04B1 in the SPring-8 synchrotron facility. We obtained new experimental results on the stability, in-situ structure, and P-V-T equations of state of Fe2P C22 phase and C23 phase up to 900 K and 11 GPa. We found that the phase transition temperature from C22 to C23 phase was about 800 K, much lower than the previously reported 1400 K [6]. Also, we found that after heating to 1200 K, the C23 phase will transform into the C22 phase. The narrow stability range of the C23 phase at low temperatures may suggest a special formation condition for nature allabogdanite in the meteorites and the C23 phase may exist in the cores of small-sized terrestrial planets with low internal pressure and temperature.
Reference: [1] Koberl et al., Proc. NIPR Symp. Antarct. Meteorites, 4, 33–55 (1991). [2] Nazarov et al., Lunar Planet. Sci. Conf., XXVIII, 1466, (1997). [3] Pataev and Wood, Lunar Planet. Sci. Conf., XXXI, 1608, (2000). [4] Ivanova et al., Lunar Planet. Sci. Conf., XXXVI, 1054, (2005). [5] Nakajima et al., Am Mineral, 105, 1752-1755, (2020). [6] Dera et al., Geophys Res Lett 35:L1030, (2008).
In this study, the phase boundary between C22 and C23 phases has been confirmed up to 17 GPa using the multi-anvil high-pressure experimental technique at beamline BL04B1 in the SPring-8 synchrotron facility. We obtained new experimental results on the stability, in-situ structure, and P-V-T equations of state of Fe2P C22 phase and C23 phase up to 900 K and 11 GPa. We found that the phase transition temperature from C22 to C23 phase was about 800 K, much lower than the previously reported 1400 K [6]. Also, we found that after heating to 1200 K, the C23 phase will transform into the C22 phase. The narrow stability range of the C23 phase at low temperatures may suggest a special formation condition for nature allabogdanite in the meteorites and the C23 phase may exist in the cores of small-sized terrestrial planets with low internal pressure and temperature.
Reference: [1] Koberl et al., Proc. NIPR Symp. Antarct. Meteorites, 4, 33–55 (1991). [2] Nazarov et al., Lunar Planet. Sci. Conf., XXVIII, 1466, (1997). [3] Pataev and Wood, Lunar Planet. Sci. Conf., XXXI, 1608, (2000). [4] Ivanova et al., Lunar Planet. Sci. Conf., XXXVI, 1054, (2005). [5] Nakajima et al., Am Mineral, 105, 1752-1755, (2020). [6] Dera et al., Geophys Res Lett 35:L1030, (2008).