Wurtzite crystal structure

Crystal Structure. Diamonds prepared by the direct conversion of well-crystallized graphite, at pressures of about 13 GPa (130 kbar), show certain unusual reflections in the x-ray diffraction patterns (25). They could be explained by assuming a hexagonal diamond stmcture (related to wurtzite) with a = 0.252 and c = 0.412 nm, space group P63 /mmc — Dgj with four atoms per unit cell. The calculated density would be 3.51 g/cm, the same as for ordinary cubic diamond, and the distances between nearest neighbor carbon atoms would be the same in both hexagonal and cubic diamond, 0.154 nm. 

Diamond is an important commodity as a gemstone and as an industrial material and there are several excellent monographs on the science and technology of this material [3-5]. Diamond is most frequently found in a cubic form in which each carbon atom is linked to fom other carbon atoms by sp ct bonds in a strain-free tetrahedral array. Fig. 2A. The crystal stmcture is zinc blende type and the C-C bond length is 154 pm. Diamond also exists in an hexagonal form (Lonsdaleite) with a wurtzite crystal structure and a C-C bond length of 152 pm. The crystal density of both types of diamond is 3.52 g-cm. ... 

Figure 29.1 Crystal structures of ZnS. (a) Zinc blende, consisting of two, interpenetrating, cep lattices of Zn and S atoms displaced with respect to each other so that the atoms of each achieve 4-coordination (Zn-S = 235 pm) by occupying tetrahedral sites of the other lattice. The face-centred cube, characteristic of the cep lattice, can be seen — in this case composed of S atoms, but an extended diagram would reveal the same arrangement of Zn atoms. Note that if all the atoms of this structure were C, the structure would be that of diamond (p. 275). (b) Wurtzite. As with zinc blende, tetrahedral coordination of both Zn and S is achieved (Zn-S = 236 pm) but this time the interpenetrating lattices are hexagonal, rather than cubic, close-packed.

A similar distortion may occur in some crystals with the wurtzite structure. Wurtzite and greenockite show easy prismatic cleavage and difficult basal cleavage, whereas iodyrite, Agl, cleaves perfectly on the... 

The XRD pattern of the as-prepared ZnSe nanoparticles (Figure 3) exhibited predominantly wurtzite crystal structure with distinct diffraction peaks corresponding to the crystalline planes of hexagonal ZnSe and lattice constant of 0.397 nm, which was... 

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))...

Non-aqueous electrolytes have been used for the preparation of CdS, CdSe, and CdTe nanowire arrays by dc electrodeposition in porous AAO templates of various pore diameters [155, 156]. For instance, CdSe NW arrays with uniform wurtzite crystal structure were fabricated from a non-aqueous DMSO solution containing CdCl2 and elemental Se. The NWs were shown to be of uniform length (2-15 p.m) and diameter (about 20 nm). The c-axis, [00.2], of the grown... 

Figure 8.1.1 The ZnO or wurtzite crystal structure illustrating the tetrahedral arrangement of oxygen atoms about each zinc atom.

Since covalent bonding is localized, and forms open crystal structures (diamond, zincblende, wurtzite, and the like) dislocation mobility is very different than in pure metals. In these crystals, discrete electron-pair bonds must be disrupted in order for dislocations to move. 

The most common—and perhaps most important—hybrid orbitals are the tetrahdral ones formed by adding one s-, and three p- type orbitals. These can be arranged to form various crystal structures diamond, zincblende, and wurtzite. Combinations of the s-, p-, and d- orbitals allow 48 possible symmetries (Kimball, 1940). 

The familiar diamond structure, with each atom covalently bonded in a perfect tetrahedral fashion to its four neighbors, is adopted not only by C but also by Si and Ge. Silicon can also adopt a wurtzite structure (see below), an example of a polytype (one of several crystal structures possible for a substance having an identical chemical composition but differing in the stacking of layers, and which may exist in a metastable state after its formation at some different temperature or pressure). 

Zinc sulfide is white to gray-white or pale yellow powder. It exists in two crystalline forms, an alpha (wurtzite) and a beta (sphalerite). The wurtzite form has hexagonal crystal structure refractive index 2.356 density 3.98 g/cm3 melts at 1,700°C practically insoluble in water, about 6.9 mg/L insoluble in alkalis soluble in mineral acids. The sphalerite form arranges in cubic crystalline state refractive index 2.368 density 4.102 g/cm changes to alpha form at 1,020°C practically insoluble in water, 6.5 mg/L soluble in mineral... 

FIGURE 1.38 The crystal structure of wurtzite, ZnS. Zn, blue spheres S, grey spheres. 

STRUCTURE. CdS Can exist in three different crystal structures hexagonal (wurtzite), cubic (zincblende)— both tetrahedrally coordinated and cubic (rock-salt), which is sixfold coordinated. Except in a few cases, the rocksalt modification of CdS has been observed only at very high pressures CD films of this phase have never been reported. The other two phases have been reported to occur in CD films under various conditions. The wurtzite phase is thermodynamically slightly more stable, and invariably forms if the zincblende phase is heated above 300-400°C. The low-temperature CD method therefore can allow the formation of the zincblende phase, and this phase is commonly obtained in CD CdS films. Very often, a mixture of wurtzite and zincblende phases has been reported in the literature. There are many variables that affect the crystal structure, including the nature of the complex, the substrate, and sometimes even stirring. 

Cadmium Sulfide. CdS [1306-23-6] is dimorphic and exists in the sphalerite (cubic) and wurtzite (hexagonal) crystal structures (40). At very high pressures it may exist also as a rock-salt structure type. It is oxidized to the sulfate, basic sulfate, and eventually the oxide on heating in air to 700°C, especially in the presence of moisture (9). 

Fig. 4. Computer-generated crystal structure models nop row. left to right) Cuprite, zinc-blende, rutile, perovskite. iridymite (second row) Cristobalite. potassium dihydrogen phosphate, diamond, pyrites, arsenic (third rowt Cesium chloride, sodium chloride, wurtzite. copper, niccolite (fourth row) Spinel, graphite, beryllium, carbon dioxide, alpha i uanz. [AT T Bel Laboratories ...

Similar to the carbon system, BN exists in a soft hexagonal (h-BN) modification, a hard cubic (c-BN) one, and many others which are not very well crystallized, or amorphous. The properties of h-BN and c-BN are summarized in Table 1 [2-17], and the crystal structures of c-BN, w-BN (wurtzitic-BN), and h-BN are illustrated in Fig. 1. 

Compounds with the wurtzite structure are shown in Table 6.2. 6.2.2. The 2-2PT Crystal Structure of I/, Ice... 

---