High-pressure phase transitions and equations of state in NiSi. II. Experimental results
High-pressure phase transitions and equations of state in NiSi. II. Experimental results
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DOI：
10.1107/s0021889812016809
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发表时间：
2012-08-01
影响因子：
6.1
通讯作者：
Walter, Michael J.
中科院分区：
文献类型：
--
作者：
Lord, Oliver T.;Vocadlo, Lidunka;Walter, Michael J.
用同步辐射X射线粉末衍射技术研究了124 GPa下激光加热金刚石对顶砧淬火样品的一硅化镍（NiSi）的高压结构，并确定了其中3个相的室温状态方程。NiSi从MnP（B31）结构（空间群Pnma）转变为？-在12.5 +/- 4.5 GPa和1550 +/- 150 K下的FeSi（B20）结构（空间群P213）。进一步压缩后，CsCl（B2）结构（空间群Pm 3 m）在46 +/-3GPa和1900 +/- 150 K下变得稳定。因此，NiSi将在整个地球地幔的大部分和整个地核中处于B2结构中，并且可能与FeSi形成固溶体，FeSi已经知道经历B20？高压下的B2转变。淬火（室温）样品的所有三个阶段的数据已被拟合到三阶BirchMurnaghan状态方程。对于MnP（B31）结构，这产生K 0 = 165 +/-3 GPa，其中K 0 '固定在4，V0固定在12.1499埃3原子-1 [V0来自同一批起始材料上未发表的中子衍射测量; Wood（2011），个人交流]。对于ε-FeSi（B20）结构，K 0 =161+/-3GPa和K 0 ' = 5.6 +/- 0.2，其中V0固定在11.4289埃3原子-1。对于CsCl（B2）结构，K 0 = 200 +/- 9 GPa，K 0 ' = 4.6 +/- 0.1，V0 = 11.09 +/- 0.05埃3原子-1。因此，NiSi的环境体积在第一相变处减小6%，然后在向CsCl结构的过渡处进一步减小3%。已经检测到由Vocadlo，Wood和多布森[J. Appl. Cryst.（2012），45，186196;第I部分]预测的并且在其中标记为Pbma-I、Pnma-II以及可能还有Pnma-III和P4/nmm的附加NiSi结构的痕迹。
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 ?-FeSi (B20) structure (space group P213) at 12.5 +/- 4.5 GPa and 1550 +/- 150 K. Upon further compression, the CsCl (B2) structure (space group Pm3m) 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 BirchMurnaghan equation of state. For the MnP (B31) structure this yields K0 = 165 +/- 3 GPa with K0' fixed at 4 and V0 fixed at 12.1499 angstrom 3 atom-1 [V0 from unpublished neutron diffraction measurements on the same batch of starting material; Wood (2011), personal communication]. For the epsilon-FeSi (B20) structure, K0 =161+/- 3 GPa and K0' = 5.6 +/- 0.2 with V0 fixed at 11.4289 angstrom 3 atom-1. For the CsCl (B2) structure, K0 = 200 +/- 9 GPa, K0' = 4.6 +/- 0.1 and V0 = 11.09 +/- 0.05 angstrom 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 Vocadlo, Wood & Dobson [J. Appl. Cryst. (2012), 45, 186196; part I], and labelled therein as Pbma-I, Pnma-II, and possibly also Pnma-III and P4/nmm, have been detected.