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

Abstract

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

Topics

• impedance spectroscopy
• phase
• experiment
• simulation
• phase diagram
• phase boundary