New insights into the compressibility and high-pressure stability of Ni(CN)2: a combined study of neutron diffraction, Raman spectroscopy, and inelastic neutron scattering
New insights into the compressibility and high-pressure stability of Ni(CN)2: a combined study of neutron diffraction, Raman spectroscopy, and inelastic neutron scattering
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DOI：
10.1088/0953-8984/28/4/045402
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发表时间：
2014-09
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通讯作者：
S. Mishra;R. Mittal;M. Zbiri;R. Rao;P. Goel;S. Hibble;A. Chippindale;T. Hansen;H. Schober;S. Chaplot
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作者：
S. Mishra;R. Mittal;M. Zbiri;R. Rao;P. Goel;S. Hibble;A. Chippindale;T. Hansen;H. Schober;S. Chaplot
氰化镍是一种层状材料，表现出明显的各向异性行为。高压中子衍射测量表明，在压力高达20.1千巴，压缩性是高得多的方向垂直于层，c，比在强化学键合的金属氰化物片的平面。详细研究了四方晶格参数a和c随压力变化的行为，揭示了斜率发生较大变化的区域，例如，在1千巴时c（P）。体积数据的实验压力依赖性在0-1 kbar的压力范围内拟合到1050（20）kbar的体积模量B 0，并且在1-20.1 kbar的范围内拟合到124（2）kbar。拉曼光谱测量产生关于Ni（CN）2层中的结构和键合如何随压力变化的额外信息，并且显示在约1千巴下发生相变。新的高压相（相PII）具有有序的氰化物基团，具有包含Ni（CN）4和Ni（NC）4基团的D4 h对称性片。相PII的拉曼光谱与相关层状化合物Cu 1/2 Ni 1/2（CN）2的光谱非常相似，该化合物先前已被证明含有有序的C N基团。的相变，PI到PII，也观察到在非弹性中子散射的研究，其中显示显着的变化发生在声子谱的压力从0.3到1.5千巴。这些变化反映了层间距的大幅减少，这发生在相位PI转换到相位PII和随之而来的增加，在平面外的原子运动的难度。与其他氰化物材料（例如Zn（CN）2和Ag 3Co（CN）6）不同，它们在低得多的压力（~100 kbar）下显示出非晶化和/或分解，Ni（CN）2可以在加压至200 kbar后回收，尽管是以更有序的形式。
Nickel cyanide is a layered material showing markedly anisotropic behaviour. High-pressure neutron diffraction measurements show that at pressures up to 20.1 kbar, compressibility is much higher in the direction perpendicular to the layers, c, than in the plane of the strongly chemically bonded metal-cyanide sheets. Detailed examination of the behaviour of the tetragonal lattice parameters, a and c, as a function of pressure reveal regions in which large changes in slope occur, for example, in c(P) at 1 kbar. The experimental pressure dependence of the volume data is fitted to a bulk modulus, B0, of 1050 (20) kbar over the pressure range 0–1 kbar, and to 124 (2) kbar over the range 1–20.1 kbar. Raman spectroscopy measurements yield additional information on how the structure and bonding in the Ni(CN)2 layers change with pressure and show that a phase change occurs at about 1 kbar. The new high-pressure phase, (Phase PII), has ordered cyanide groups with sheets of D4h symmetry containing Ni(CN)4 and Ni(NC)4 groups. The Raman spectrum of phase PII closely resembles that of the related layered compound, Cu1/2Ni1/2(CN)2, which has previously been shown to contain ordered C≡N groups. The phase change, PI to PII, is also observed in inelastic neutron scattering studies which show significant changes occurring in the phonon spectra as the pressure is raised from 0.3 to 1.5 kbar. These changes reflect the large reduction in the interlayer spacing which occurs as Phase PI transforms to Phase PII and the consequent increase in difficulty for out-of-plane atomic motions. Unlike other cyanide materials e.g. Zn(CN)2 and Ag3Co(CN)6, which show an amorphization and/or a decomposition at much lower pressures (~100 kbar), Ni(CN)2 can be recovered after pressurising to 200 kbar, albeit in a more ordered form.