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The phase diagram of NiSi under the conditions of small planetary interiors

Dobson, D; Hunt, S; Ahmed, J; Lord, O; Wann, E; Santangeli, J; Wood, IG; ... Mezouar, M; + view all (2016) The phase diagram of NiSi under the conditions of small planetary interiors. Physics of the Earth and Planetary Interiors , 261 pp. 196-206. 10.1016/j.pepi.2016.10.005. Green open access

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Abstract

The phase diagram of NiSi has been determined using in situ synchrotron X-ray powder diffraction multi-anvil experiments to 19 GPa, with further preliminary results in the laser-heated diamond cell reported to 60 GPa. The low-pressure MnP-structured phase transforms to two different high-pressure phases depending on the temperature: the ε-FeSi structure is stable at temperatures above ∼1100 K and a previously reported distorted-CuTi structure (with Pmmn symmetry) is stable at lower temperature. The invariant point is located at 12.8 ± 0.2 GPa and 1100 ± 20 K. At higher pressures, ε -FeSi-structured NiSi transforms to the CsCl structure with CsCl-NiSi as the liquidus phase above 30 GPa. The Clapeyron slope of this transition is -67 MPa/K. The phase boundary between the ε -FeSi and Pmmn structured phases is nearly pressure independent implying there will be a second sub-solidus invariant point between CsCl, ε -FeSi and Pmmn structures at higher pressure than attained in this study. In addition to these stable phases, the MnP structure was observed to spontaneously transform at room temperature to a new orthorhombic structure (also with Pnma symmetry) which had been detailed in previous ab initio simulations. This new phase of NiSi is shown here to be metastable.

Type: Article
Title: The phase diagram of NiSi under the conditions of small planetary interiors
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.pepi.2016.10.005
Publisher version: http://dx.doi.org/10.1016/j.pepi.2016.10.005
Language: English
Additional information: © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1520946
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