Unbiased crystal structure prediction of NiSi under high pressure

TL;DR

This study uses unbiased structure prediction to identify stable phases of NiSi under high pressure, revealing new structures and phase transition sequences relevant to Earth's core conditions.

Contribution

The paper introduces a novel unbiased prediction method to determine high-pressure phases of NiSi, discovering a new stable tetragonal CsCl-type structure and detailed phase transition sequences.

Findings

Pmmn-structure stable below 213 GPa

New tetragonal CsCl-type phase stable at 213-522 GPa

Cubic CsCl structure stable above 522 GPa

Abstract

Based on the unbiased structure prediction, we showed that the stable form of NiSi compound under the pressure of 100 and 200 GPa is the Pmmn-structure. Furthermore, we discovered a new stable phase - the deformed tetragonal CsCl-type structure with a = 2.174 {\AA} and c = 2.69 {\AA} at 400 GPa. Specifically, the sequence of high-pressure phase transitions is the following: the Pmmn-structure - below 213 GPa, the tetragonal CsCl-type - in the range 213-522 GPa, and cubic CsCl - higher than 522 GPa. As the CsCl-type structure is considered as the model structure of FeSi compound at the conditions of the Earth's core, this result implies restrictions on the Fe-Ni isomorphic miscibility in FeSi.