Dynamical stability of Fe-H in the Earth's mantle and core regions

doi:10.1073/pnas.0609701104

Dynamical stability of Fe-H in the Earth's mantle and core regions

*Theoretical Physics Department, Moscow State Institute of Steel and Alloys (Technological University), 4 Leninskii Prospect, Moscow 119049, Russia;
^†Condensed Matter Theory Group, Physics Department, Uppsala University, SE-751 21 Uppsala, Sweden;
^‡Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden; and
^§School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China

Edited by Ho-kwang Mao, Carnegie Institution of Washington, Washington, DC, and accepted March 14, 2007 (received for review November 1, 2006)

Abstract

The core extends from the depth of 2,900 km to the center of the Earth and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp → hcp → fcc sequence of structural transitions.

Footnotes

^¶To whom correspondence should be addressed. E-mail: borje.johansson{at}fysik.uu.se
Author contributions: N.V.S., R.A., and B.J. designed research; E.I.I. performed research; E.I.I., N.V.S., R.A., Y.K.V., and B.J. analyzed data; and E.I.I., N.V.S., and R.A. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations:

HF,

high frequency;

LF,

low frequency.