Sphalerite structure cubic

B3 is the sphalerite structure (cubic) and B4 the wurtzite structure (hexagonal). The experimental values are from Strukturbericht and Structure Reports, except for BN, which is from R. H. Wentorf, Jr., J. Ckem. Phys. 26, 956 (1957). 

When the radius ratio of an ionic compound is less than about 0.4, corresponding to cations that are significantly smaller than the anion, the small tetrahedral holes may be occupied. An example is the zinc-blende structure (which is also called the sphalerite structure), named after a form of the mineral ZnS (Fig. 5.43). This structure is based on an expanded cubic close-packed lattice of the big S2 anions, with the small Zn2+ cations occupying half the tetrahedral holes. Each Zn2+ ion is surrounded by four S2 ions, and each S2" ion is surrounded by four Zn2+ ions so the zinc-blende structure has (4,4)-coordination. 

FIGURE 5.43 Hie zinc-blende (sphalerite) structure, rhe tour zinc ions (pink) form a tetrahedron within a face-centered cubic unit cell composed of sulfide ions (vellow).The zinc ions occupy half the tetrahedral holes between the sulfide ions, and the parts or the unit cell occupied by zinc ions are shaded blue. The detail shows how each zinc ion is surrounded by four sulfide ions each sulfide ion is similarly surrounded by four zinc ions. 

Ziegler-Natta catalyst A stereospecific catalyst for polymerization reactions, consisting of titanium tetrachloride and triethylaluminum. zinc-blende structure A crystal structure in which the cations occupy half the tetrahedral holes in a nearly close packed cubic lattice of anions also known as sphalerite structure. 

The cubic zinc blende or sphalerite structure of ZnS is similar to that of diamond but with alternating sheets of Zn and S stacked parallel to the axes, replacing C. 

Sphalerite and wurtzite structures general remarks. Compounds isostructural with the cubic cF8-ZnS sphalerite include AgSe, A1P, AlAs, AlSb, BAs, GaAs, InAs, BeS, BeSe, BeTe, BePo, CdS, CdSe, CdTe, CdPo, HgS, HgSe, HgTe, etc. The sphalerite structure can be described as a derivative structure of the diamond-type structure. Alternatively, we may describe the same structure as a derivative of the cubic close-packed structure (cF4-Cu type) in which a set of tetrahedral holes has been filled-in. This alternative description would be especially convenient when the atomic diameter ratio of the two species is close to 0.225 see the comments reported in 3.7.3.1. In a similar way the closely related hP4-ZnO... 

One example is the tertiary bond found in the wurtzite structure of ZnO (67454). All members of the Zn chalcogenide series crystallize with structures based on the close packing of the chalcogenide ions, with Zn occupying half the tetrahedral cavities. The higher members, ZnSe and ZnTe (31840), crystallize with the cubic sphalerite structure while ZnO crystallizes with the hexagonal wurtzite structure. ZnS (60378, 67453) is known in both forms. 

In the sphalerite structure the anions form a cubic close packed array. The structure has a single adjustable parameter, the cubic cell edge. The 0 ions are too small for them to be in contact in this structure (see Fig. 6.4) so ZnO adopts the lower symmetry hexagonal wurtzite structure which has three adjustable parameters, the a and c unit cell lengths and the z coordinate of the 0 ion, allowing the environment around the Zn " ion to deviate from perfect tetrahedral symmetry. In the sphalerite structure the ZnX4 tetrahedron shares each of its faces with a vacant octahedral cavity (one is shown in Fig. 2.6(a)), while in the wurtzite structure one of these faces is shared with an empty tetrahedral cavity which places an anion directly over the shared face as seen in Fig. 2.6(b). The primary coordination number of Zn " in sphalerite is 4 and there are no tertiary bonds, but in wurtzite, which has the same primary coordination number, there is an additional tertiary bond with a flux of 0.02 vu through the face shared with the vacant tetrahedron. 

AIN, GaN and InN crystallise in the wurtzite structure which is characterised by lattice parameters a and c, as well as by u-value (u = b/c, where b is a bond-length in the c-direction). For the ideal wurtzite structure, c/a = 1.633 and u = 0.375. In contrast to the cubic sphalerite structure, the wurtzite structure offers two possibilities to deviate from the ideal arrangement, by changing the c/a ratio and by changing the u value. Such deviations are often observed in wurtzite-type structures [1] but there exists a strong correlation between the c/a ratio and the u parameter if c/a decreases, then u increases in such a way that the four tetrahedral distances remain nearly constant and the tetrahedral angles are distorted [2]. The bond lengths would be equal if ... 

When the hard-sphere cation-anion radius ratio exceeds 0.732, as it does for the cesium halides, a different crystal structure called the cesium chloride structure, is more stable. It may be viewed as two interpenetrating simple cubic lattices, one of anions and the other of cations, as shown in Figure 21.17. When the cation-anion radius ratio is less than 0.414, the zinc blende, or sphalerite, structure (named after the structure of ZnS) results. This crystal consists of an fee lattice of... 

Figure 7.22 Three-dimensional nets (a) the cubic diamond structure (b) the net equivalent to (a) (c) the cubic zinc blende (sphalerite) structure (d) the net equivalent to (c), which is identical to that in (b) (e) the hexagonal wurtzite structure (f) the net equivalent to (e)...

Silicon carbide, carborundum, also crystallises in two forms, of which /(-SiC has the cubic zinc blende (sphalerite) structure (Figure 8.8a). When viewed along the cube face-diagonal [110] direction, the layers of both silicon and carbon are packed in the cubic closest packing arrangement. .. aAbBcCaAbBcC. .., where the uppercase and lowercase letters stand for layers of Si and C. The other form of silicon carbide, a-SiC, is a collective name for the various silicon carbide polytypes, which consist of complex arrangements of zinc blende and wurtzite slabs. Some of these are known by names such as carborundum I, carborundum II, carborundum III, and so on. One of the simplest structures is that of carbo-... 

Silver iodide undergoes a first order structural phase transition at 420 K from the / -phase (hexagonal Wurtzite structure), which is metastable with respect to the / -phase (cubic sphalerite structure), to the a-phase where the I - ions occupy a bcc lattice within which the Ag+ ions jump rapidly between a number of possible sites. The ionic conductivity is very high upon melting it actually decreases. Agl is probably the most widely studied fast ion conductor, with much of the work concentrating on determination of the exact distribution of Ag+ sites and conduction pathways. 

The most important MX structures involving tetrahedral coordination are the cubic ZnS sphalerite (Fig. 5a) and the hexagonal ZnS wurtzite (Fig. 5b) arrangements. It is striking that halides and sulfides of metal ions with d5 and d10 shells have a tendency to crystallize in the sphalerite structure for example, the cuprous halides, Agl, HgS, MnS, CdS, and ZnS. (The last three also occur in the wurtzite modification, as do the oxides of Zn and Be). (See Table V.) Here again, the simple ionic theory fails to account for the facts for (1) the radius ratios of some of these compounds are compatible with a 6-coordinated structure, and (2) interatomic distances calculated from the usual ionic radii (decreased by 5% to com-... 

Minor (<5%) quantities of cubic phase (a0 = 6.24 A, zincblende sphalerite structure, space group F 43m) may sometimes be present. Further annealing of the sample will cause transformation of all the material into the hexagonal phase. 

Farneth et al. have investigated the mechanism of the solid-state conversion of a series of II-VI precursors of general formula (R4N )4[S4Mio(SPh)i6]" (R = Me, Et M = Gd, Zn) to the bulk metal sulphide structure. The transformation, as followed by combined TGA and mass spectroscopy, proceeds in two discrete reaction steps. In the case of cadmium derivative, the loss of countercations around 200 °G produces a new molecular solid, which was characterized (X-ray) to be GdioSi6Phi2. This intermediate composition gave a broad X-ray diffraction pattern that indicated very small (<25 A) sphalerite-phase (cubic) crystals of GdS. The second decomposition reaction eliminates S6Phi2 around 350 °G and produces phase-pure GdS (wurtzite) (Equation (5)). 

The zinc blende or sphalerite structure in Table 12.1 consists of a face-centered cubic lattice of the anions, but with the cations occupying only every other tetrahedral hole. Compounds that assume this structure therefore have a I I ratio and include the following species BeO, BeS, ZnO, ZnS, ZnSe, MnS, CdS, HgS, SiC, GaP, AlP, InAs, CuF, and CuCI. 

Figure 4.12. Two modifications of boron nitride, which is isoelectronic with carbon (a) layered hexagonal a-BN, and (b) cubic ) -BN with a sphalerite structure. Both are electrical insulators, but like carbon they are either very soft or very hard.

Diamond-Like Boron Nitride Modifications Cubic Boron Nitride with Sphalerite Structure (P-BN)... 

---