Report for the Joint Use/Research of the Institute for Planetary Materials,
Okayama University
2022 fiscal year first term / second term / others
29/5/2023
Category:

International Joint Research/ General Joint Research/ Joint Use of Facility/ Workshop

Name of the research project: Studies of the P-V-T equations of state of (Fe,Ni)2P and the P-T
conditions of the “C22 to C23” phase transition
Principal applicant: Xuejing He
Affiliated institution and department: Geochemical Research Center, Graduate School of Science,
The University of Tokyo
Collaborator
Name:
Youyue Zhang, Takashi Yoshino
Hiroyuki Kagi
Affiliated institution and department:
IPM
Geochemical Research Center, Graduate School of Science, The University of Tokyo
Research report:
1. Research purpose
Iron-nickel

phosphides,suchas

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, inthe 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 high-pressure andhigh-temperature the Fe-Ni-P system are essential for constraints on physical and chemical
properties of planetary cores and P-T histories of meteorites.
Despite the significance, the study of this issue is not adequate. Fe2P has been observed totransform from barringerite (P-62m, C22) to allabogdanite (Pnma, C23) at 8 GPa and 1400 K, andthe latter could be quenched to ambient conditions as a metastable phase [6]. However, the phaseboundary of the C22 and C23 phases has not been well studied. The insufficient knowledge of thethermal equations of state (P-V-T EOS) and pressure-temperature (P-T) phase diagrams of the Fe2P
polymorphs limits fully characterization of the Fe-P system at high pressure and temperature. In thisstudy, we plan to investigate the P-V-T EOS of allabogdanite Fe2P and the P-T phase diagram ofbarringerite-allabogdanite (Fe1-xNix)2P.
2. Actually conducted research(1) P-V-T EOS of allabogdanite Fe2P and P-T phase diagram of barringerite-allabogdanite Fe2PP-V-T equations of state of allabogdanite Fe2P has been obtained up to 900 K and 11 GPausing the multi-anvil high-pressure experimental technique at beamline BL04B1 in the SPring-8
synchrotron facility. The phase boundary between C22 and C23 phases has been confirmed up to 17GPa. Up to 5 GPa, the phase transition temperature from C22 to C23 was found at about 800 K,
which is much lower than the previously reported 1400 K [6]. And 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.
(2) P-T phase diagram of barringerite-allabogdanite (Fe1-xNix)2PBarringerite (Fe1-xNix)2P with various Ni contents, i.e., Fe2P, Fe1.9Ni0.1P, Fe1.5Ni0.5P, and Ni2P,
were synthesized using a 14/8 cell assembly on the USSA-1000 multi-anvil apparatus at IPM. Forstudying the phase diagram, quenched experiments were performed at 8 GPa and 800, 900, 1000,1100 K, kept for 12 h, using the USSA-1000 multi-anvil apparatus. Four barringerite samples, i.e.,
Fe2P, Fe1.9Ni0.1P, Fe1.5Ni0.5P, and Ni2P, were loaded in one 14/8 cell assembly. Recovered samples
were characterized using micro-focused X-ray diffraction. Phases were confirmed as shown in Fig.
1. The allabogdanite (Fe1-xNix)2P existed in a narrow T range, and increasing Ni content played anegative role in its stability.

Figure 1. Phase diagram of barringerite-allabogdanite (Fe1-xNix)2P at 8 GPa, 800-1100 K.

References[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).
3. Research outcomes○Zhang Y.*, He X., Yoshino T. (2023) Studies of the P-V-T equations of state of Fe2P and the P-T
conditions of the “C22 to C23” phase transition. IN: Japan Geoscience Union Meeting 2023:
SIT18-P04. May 2023. Makuhari Messe, Chiba, Japan (Poster)
Zhang Y., He X., Yoshino T., Kagi H. P-V-T equations of state of allabogdanite Fe2P and the “C22to C23” phase transition of (Fe1-xNix)2P. (Research paper in preparation)