NiAs crystal structure

LaNis has the CaCu, structure, space group P6/mmm [26] the hexagonal metal lattice is shown in Fig. 4. The crystal structure of LaNi5D7 has been determined 127, 28] and is illustrated in Fig. 5. There are three types of interstitial D sites La2Ni4 tetrahedra, and NiA tetrahedra. The unit cell is doubled along the oaxis because of the formation of a superlattice which is a consequence of long-range correlations between occupied and unoccupied... 

Fig. 1.2 Crystal structures of the major sulfides (metal atoms are shown as smaller or black spheres) (A) galena (PbS) structure (rock salt) (B) sphalerite (ZnS) structure (zinc blende) (C) wurtzite (ZnS) strucmre (D) pyrite structure and the linkage of metal-sulfur octahedra along the c-axis direction in (/) pyrite (FeSa) and (//) marcasite (FeSa) (E) niccolite (NiAs) structure (F) coveUite (CuS) structure (layered). (Adapted from Vaughan DJ (2005) Sulphides. In Selley RC, Robin L, Cocks M, Plimer IR (eds.) Encyclopedia of Geology, MINERALS, Elsevier p 574 (doi 10.1016/B0-12-369396-9/00276-8))...

In the crystal structure of nickel asenide, NiAs, the As atoms are in hep with all octahedral interstices occupied by the Ni atoms, as shown in Fig. 10.2.3(a). An important feature of this structure is that the Ni and As atoms are in different coordination environments. Each As atom is surrounded by six equidistant Ni atoms situated at the corners of a regular trigonal prism. Each Ni atom, on the other hand, has eight close neighbors, six of which are As atoms arranged octahedrally about it, while the other two are Ni atoms immediately above and belowitatz = c/2. The Ni-Ni distance is c/2 = 503.4/2 = 251.7 pm, which corresponds to the interatomic distance in metallic nickel. Compound NiAs is semi-metallic, and its metallic property results from the bonding between Ni atoms. In the NiAs structure, the axial ratio da = 503.4/361.9 = 1.39 is much... 

A number of important structure types are found in transition-metal sulphides which have no counterparts among oxide structures, notably the various layer structures and the pyrites, marcasite, and NiAs structures. Further, many sulphides, particularly of the transition metals, behave like alloys, the resemblance being shown by their formulae (in which the elements do not exhibit their normal chemical valences, as in 0983, Pd4S, TiSa), their variable composition, and their physical properties-metallic lustre, reflectivity, and conductivity. The crystal structures of many transition-metal sulphides show that in addition to M-S bonds there are metal-metal bonds as, for example, in monosulphides with the NiAs structure (see later), in chromium sulphides, and in many sub-sulphides such as Hf2S,... 

Here the = (mi x + m2 y + m3 z)a are the positions of the ions. We see immediately that there are as many values of k as there are chlorine ions these correspond to the conservation of chlorine electron states. We also see that the wave functions for states of different k are orthogonal to each other. Values for k run almost continuously over a cubic region of wave number space, — n/a < k < nia, — nja Brillouin Zone, here cubic, depends upon the crystal structure.) For a macroscopic crystal the Af, are very large, and the change in wave number for unit change in is very tiny. Eq. (24) is an exact solution of Eq. (2-2) however, we will show it for only the simplest approximation, namely, for the assumption that the s,) are sufficiently localized that we can neglect the matrix element Hji = (sj H s,) unless (1) two states in question are the same (/ = j) or... 

The phase CU3AI2 has a crystal structure of the partially filled NiAs type, and CuAl has a structure which may be described as a vacancy variant of the CsCl structure. ... 

It has been shown [123] that the metal sub-lattice in crystal structures of the ZnS, NaCl, NiAs and CsCl types has the same (or similar) Nc of metal and M-M distances (< mm), as the structure of pure metal ( mm) hence the degree of metallic bonding can be defined as... 

Figure 9 Crystal structure of NiAs-type lanthanum monoiodide, Lai...

CdSjTl P3ml a=3.645 c = 6.810 Z=1 Ordered NiAs-type. X, single crystal, structure complete. 69Gus2, 67Gusl )... 

A number of selenium and tellurium compounds of the presently discussed metals show a quite different behavior from the Fe-S system. Iron and selenium form two compounds FeSe with a broad stoichiometry range and FeSe2 with a much narrower composition field. Below 400 the non-stoichiometric Fei xSe exists by creation of iron vacancies and can have compositions lying between FeySes and Fe3Se4. At low temperatures there exist two phases an a (PbO type) and a f) (NiAs type) phase. The crystal sUiicture of the diselenide, FeSe2, is an orthorhombic, C18 (marcasite) type. In the Fe-Te system, the defect NiAs structure is found at a composition close to FeTei.s, as about one-third of the Fe atoms are missing. At compositions around FeTe the behavior is complex, and the f)-phase has the PbO structure (like FeSe) but with additional metal atoms (i.e., FeuTe). 

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