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High‐pressure phase transitions and equations of state in NiSi. II. Experimental results
Author(s) -
Lord Oliver T.,
Vočadlo Lidunka,
Wood Ian G.,
Dobson David P.,
Clark Simon M.,
Walter Michael J.
Publication year - 2012
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889812016809
Subject(s) - diamond anvil cell , crystallography , powder diffraction , neutron diffraction , diffraction , equation of state , materials science , inner core , crystal structure , synchrotron , phase (matter) , atom (system on chip) , phase transition , space group , high pressure , x ray crystallography , chemistry , analytical chemistry (journal) , thermodynamics , physics , optics , organic chemistry , chromatography , computer science , embedded system , composite material
The high‐pressure structures of nickel monosilicide (NiSi) have been investigated to 124 GPa by synchrotron‐based X‐ray powder diffraction studies of quenched samples from laser‐heated diamond anvil cell experiments, and the equations of state of three of these phases have been determined at room temperature. NiSi transforms from the MnP (B31) structure (space group Pnma ) to the ɛ‐FeSi (B20) structure (space group P 2 1 3) at 12.5 ± 4.5 GPa and 1550 ± 150 K. Upon further compression, the CsCl (B2) structure (space group Pm 3 m ) becomes stable at 46 ± 3 GPa and 1900 ± 150 K. Thus, NiSi will be in the B2 structure throughout the majority of the Earth's mantle and its entire core, and will likely form a solid solution with FeSi, which is already known to undergo a B20 → B2 transition at high pressure. Data from the quenched (room‐temperature) samples of all three phases have been fitted to the third‐order Birch–Murnaghan equation of state. For the MnP (B31) structure this yields K 0 = 165 ± 3 GPa with K 0 ′ fixed at 4 and V 0 fixed at 12.1499 Å 3 atom −1 [ V 0 from unpublished neutron diffraction measurements on the same batch of starting material; Wood (2011), personal communication]. For the ɛ‐FeSi (B20) structure, K 0 =161± 3 GPa and K 0 ′ = 5.6 ± 0.2 with V 0 fixed at 11.4289 Å 3 atom −1 . For the CsCl (B2) structure, K 0 = 200 ± 9 GPa, K 0 ′ = 4.6 ± 0.1 and V 0 = 11.09 ± 0.05 Å 3 atom −1 . The ambient volume of NiSi, therefore, decreases by 6% at the first phase transition and then by a further 3% at the transition to the CsCl structure. Traces of additional NiSi structures predicted by Vočadlo, Wood & Dobson [ J. Appl. Cryst . (2012), 45 , 186–196; part I], and labelled therein as Pbma ‐I, Pnma ‐II, and possibly also Pnma ‐III and P 4/ nmm , have been detected.