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

David P Dobson, Simon A Hunt, Jabraan Ahmed, Oliver T Lord, Elizabeth TH Wann, James Santangeli, Ian G Wood, Lidunka Vočadlo, Andrew M Walker, Andrew R Thomson, Marzena A Baron, Hans J Mueller, Christian Lathe, Matthew Whitaker, Guillaume Morard, Mohamed Mezouar

Research output: Contribution to journalArticle (Academic Journal)peer-review

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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.
Original languageEnglish
Pages (from-to)196–206
Number of pages11
JournalPhysics of the Earth and Planetary Interiors
Volume261 Part B
Early online date14 Oct 2016
DOIs
Publication statusPublished - Dec 2016

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