Title: Elastic and magnetic properties of Fe₃P up to core pressures: Phosphorus in the Earth's core

Abstract

Phosphorus (P) is considered a possible light element alloying with iron (Fe) in the Earth's core due to its siderophile nature and the ubiquity of P-bearing iron alloys in iron meteorites. The sequestration of P by liquid metals during the core formation possibly results in the relatively low concentration of P in the bulk silicate Earth. Here, we performed single-crystal and powder X-ray diffraction, synchrotron Mossbauer spectroscopy and nuclear resonant inelastic X-ray scattering measurements in diamond anvil cells to investigate the elastic and magnetic properties of Fe₃P under high pressures. Our X-ray diffraction results suggest that there is no structural phase transition up to 111 GPa. However, a volume collapse was observed at 21.5 GPa in Fe₃P, ascribed to a magnetic transition as evidenced by synchrotron Mhssbauer spectroscopy results. Fitting the volume-pressure data by the Birch-Murnaghan equation of state gives bulk modulus $$K_{T0}$$ = 162.4(7) GPa, its first pressure derivative $$K'_{T0}$$ = 4.0 (fixed) and zeropressure volume $$V_0$$ = 370.38(6) ų for the magnetic phase and $$K_{T0}$$ = 220(7) GPa, $$K'_{T0}$$ = 4.0 (fixed) and $$V_0$$ = 357(1) ų for the non-magnetic phase. Sound velocities of Fe₃P were determined up to 152 GPa by nuclear resonant inelastic X-ray scattering, demonstrating that Fe₃P bears a low shear velocity and high Poisson's ratio at core pressures compared to Fe and Fe₃S. When forming a solid solution Fe₃(S,P) with Fe₃S at core pressures, Fe₃P may favorably influence the elastic properties of Fe₃(S,P) to match the seismic observations of the inner core.

Authors:

Lai, Xiaojing  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-4451-9421"

Zhu, Feng  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-2409-151X"

Liu, Yingxin ^[1]; Bi, Wenli ^[3]; Zhao, Jiyong ^[4]; Alp, E. Ercan ^[4]; Hu, Michael Y. ^[4]; Zhang, Dongzhou  ^[5];

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• Search DOE PAGES for ORCID "0000-0002-6679-892X"

Tkachev, Sergey ^[6]; Manghnani, Murli H. ^[2]; Prakapenka, Vitali B. ^[6]; Chen, Bin  ^[2]

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• Search DOE PAGES for ORCID "0000-0001-8314-9991"

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+ Show Author Affiliations

1. Univ. of Hawaii at Manoa, Honolulu, HI (United States); China Univ. of Geosciences, Wuhan (China)
2. Univ. of Hawaii at Manoa, Honolulu, HI (United States)
3. Argonne National Lab. (ANL), Chicago, IL (United States). Advanced Photon Source (APS); Univ. of Alabama, Birmingham, AL (United States)
4. Argonne National Lab. (ANL), Chicago, IL (United States). Advanced Photon Source (APS)
5. Univ. of Hawaii at Manoa, Honolulu, HI (United States); Univ. of Chicago, IL (United States)
6. Univ. of Chicago, IL (United States)

Publication Date:

Tue Nov 26 00:00:00 EST 2019

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)

Sponsoring Org.:

National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; Consortium for Materials Properties Research in Earth Sciences (COMPRES)

OSTI Identifier:

1615477

Alternate Identifier(s):

OSTI ID: 1703134

Grant/Contract Number:  

AC02-06CH11357; FG02-94ER14466

Resource Type:

Accepted Manuscript

Journal Name:

Earth and Planetary Science Letters

Additional Journal Information:

Journal Volume: 531; Journal ID: ISSN 0012-821X

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; core composition; density; iron phosphide; light elements; magnetic transition; sound velocities