Sphalerite or Zinc Blende

Thus MgTe with r+/r = 0.37 and BeO (0.26) possess a tetrahedral arrangement (sphalerite or zinc blende structure),... 

The principal ore of zinc is sphalerite or zinc blende, ZnS. Less important ores include zincite, ZnO smithsonite, ZnCO, xoillemite, ZiioSiO calamine, Zi, SiC). (()H).. and franklinitr, Fe.,Zn04. 

Zinc never occurs as a free element in the earth. Some of its most important ores include smithsonite, or zinc spar or zinc carbonate (ZnC03) sphalerite, or zinc blende or zinc sulfide (ZnS) zincite, or zinc oxide (ZnO) willemite, or zinc silicate (ZnSi03) and franklinite [(Zn,Mn,Fe)0 (Fe,Mn2)03]. 

Recently, Mg and Be compounds have been used in alloys with ZnSe to make blue and green semiconductor lasers. Bulk growth by zone melting and molecular beam epitaxy (MBE) ° has been used. In these cases, good semiconductor material has been obtained dilution with group IIB compounds may be responsible. However, growth of pure MgS in very thin films on ZnSe has been achieved the epitaxial orientation effect of the substrate results in a tetrahedral cubic (sphalerite or zinc-blende) structure. It is likely that improvements in these materials will take place at a rapid rate, driven in part by applications and in part by newer, cleaner synthetic methods. 

The diamond structure and the cubic ZnS (sphalerite or zinc-blende) structure can be seen as the superposition of two identical fee Bravais sublattices translated by one quarter of the diagonal of their unit cell. In these structures,... 

Sphalerite or zinc blende (figure M47) is a yellow, brown, or black mineral (Zn,Ee)S. It often contains manganese, arsenic, cadmium and other elements. It is a widely distributed ore of zinc, commonly associated with galena PbS in veins and other deposits. Sphalerite is the principal ore mineral for zinc in the world. 

Sphalerite or zinc blende is the chief ore of ZnS. ZnS as well as many of the III-V and II-VI compound semiconductors such as GaAs form a diamond-like stmeture with one type of atom on the fee lattice sites and the other type of atom on every other tetrahedral site. The space group is F43wx (the d-glide plane symmetry in diamond is lost by the fact that different atoms occupy the interstitial sites). Since there are four atoms on the lattice points of the fee unit cell, the stoichiometry is maintained if half of the eight tetrahedral sites are occupied by the second atom. For these systems, the double stacking described above would have different atoms in doubled layers, i.e., A(Zn) A (S) B(Zn) B (S) C(Zn) C (S), etc. This type of structure is the same as shown in Figure 5.9 if the black spots are... 

BN has at least four crystal structures, namely, hexagonal (h-BN), cubic or zinc blende or sphalerite (c-BN), wurtzite (w-BN), and rhombohedral (r-BN). Among these, the... 

C, b.p. 907"C, d 713. Transition element occurring as zinc blende, sphalerite (Zn,Fe)S calamine or smithsonite (ZnCO j), willemite (Zo2Si04), franklinite (ZnFe204). Extracted by roasting to ZnO and reduction with carbon. The metal is bluish-white (deformed hep) fairly hard and brittle. Burns... 

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. 

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))...

For compounds of the composition MX (M = cation, X = anion) the CsCl type has the largest Madelung constant. In this structure type a Cs+ ion is in contact with eight Cl-ions in a cubic arrangement (Fig. 7.1). The Cl- ions have no contact with one another. With cations smaller than Cs+ the Cl- ions come closer together and when the radius ratio has the value of rM/rx = 0.732, the Cl- ions are in contact with each other. When rM/rx < 0.732, the Cl- ions remain in contact, but there is no more contact between anions and cations. Now another structure type is favored its Madelung constant is indeed smaller, but it again allows contact of cations with anions. This is achieved by the smaller coordination number 6 of the ions that is fulfilled in the NaCl type (Fig. 7.1). When the radius ratio becomes even smaller, the zinc blende (sphalerite) or the wurtzite type should occur, in which the ions only have the coordination number 4 (Fig. 7.1 zinc blende and wurtzite are two modifications of ZnS). 

In theory, the III-V compound semiconductors and their alloys are made from a one to one proportion of elements of the III and V columns of the periodic table. Most of them crystallize in the sphalerite (zinc-blende ZnS) structure. This structure is very similar to that of diamond but in the III-V compounds, the two cfc sublattices are different the anion sublattice contains the group V atoms and the cation sublattice the group III atoms. An excess of one of the constituents in the melt or in the growing atmosphere can induce excess atoms of one type (group V for instance) to occupy sites of the opposite sublattice (cation sublattice). Such atoms are said to be in an antisite configuration. Other possibilities related with deviations from stoichiometry are the existence of vacancies (absence of atoms on atomic sites) on the sublattice of the less abundant constituent and/or of interstitial atoms of the most abundant one. 

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. 

The zinc that is produced today starts as the zinc sulfide (ZnS) minerals zinc blende or sphalerite or from zinc carbonate (ZnCO ) known as smithsonite or calamine. In the electrolytic process, these minerals are dissolved in water to form the electrolyte in the cell where the zinc cations are attracted and collected at the cathode and deposited as a dull, brittle type of zinc. 

Practically aU zinc produced today comes from sulfide ores, sphalerite or blende. The ore is first roasted to form zinc oxide. The primary reaction is ... 

The major ores of Zn are zinc blende ZnS (also known as sphalerite) and calamine ZnC03. Much more Zn is now produced from ZnS which is concentrated from its rock matrix by flotation or sedimentation. The concentrate is then roasted to generate ZnO, which is smelted with coke, or which is dissolved in H2SO4 and the solution is electrolyzed. 

FIGURE 1.37 The crystal structure of zinc blende or sphalerite, ZnS. Zn, blue spheres S, grey spheres (or vice versa). 

Zinc blende structure (Fig. 4-l%)- Zinc blende or sphalerite (ZnS) has a cubic structure in which we again have interchangeable, interpenetrating fee arrays of Zn2+ and S2. If, as in Fig. 4.12, we call the shaded ions zinc and divide the unit cell into eight subcubes, we see that the zinc ions occupy the body centers of every alternate subcube. Furthermore, the coordination number of each ion is now four, and the nuclei of the four nearest neighbors... 

Wurtzite structure. Zinc sulfide can also crystallize in a hexagonal form called wurtzite that is formed slightly less exothermically than the cubic zinc blende (sphalerite) modification (Afff = —192.6 and —206.0 kJ mol-1, respectively) and hence is a high temperature polymorph of ZnS. The relationship between the two structures is best described in terms of close packing (Section 4.3) in zinc blende, the anions (or cations) form a cubic close-packed array, whereas in wurtzite they form hexagonal close-packed arrays. This relationship is illustrated in Fig. 4.13 note, however, that this does not represent the actual unit cell of either form. 

We introduced the basic principles of semiconduction in Section 5.3. Many semiconductors have the cubic sphalerite (zinc blende) structure (Fig. 4.12), which is the same as the diamond lattice (Fig. 3.1) if all the atoms are the same, as in Si or Ge. Inorganic semiconductors generally have four valence electrons per atom, as is the case for Si and Ge. They can be classified according to the number of valence electrons of the participating atoms15 ... 

SPHALERITE BLENDE. Also known as zinc blende, this mineral is zinc sulfide, tZn, Fc)S, practically always containing some iron, crystallizing in the isometric system frequently as tetrahedrons, sometimes as cubes or dodecahedrons, but usually massive with easy cleavage, which is dodecahedral. It is a brittle mineral with a conchoidal fracture hardness, 2.5-4 specific gravity, 3.9-4.1 luster, adamantine to resinous, commonly the latter. It is usually some shade of yellow brown or brownish-black, less often red, green, whitish, or colorless streak, yellowish or brownish, sometimes white transparent to translucent. Certain varieties... 

When the radius ratio of an ionic compound is less than ahout 0.4, tetrahedral holes may be filled. An example of such a structure is the zinc-blende structure (or sphalerite structure), which is named after a form of the mineral ZnS (Fig. 5.46). This structure is based on an expanded cubic close-packed lattice for the anions, with the 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. 

The PT structure has filled P layers and one T layer filled between P layers. Zinc sulfide has two modifications zinc blende or sphalerite... 

There are two polymorphic structures of ZnS, zinc blende (or sphalerite) (3 2PT) and wurtzite (2 2PT). In zinc blende there is a ccp arrangement of S atoms with Zn atoms filling one of the two T layers as shown in Figure 6.1. The diamond has the same structure, with the sites of P and one T layer filled by C atoms (Section 4.3.3). The structure of zinc blende has six (3 2) layers in the repeating unit. This structure is encountered for many binary compounds with significant covalent character as shown in Table 6.1. The space group for zinc blende is T%, F43m, and a0 = 5.4093 A, for the cubic unit cell. ... 

The elements are found in nature as sulphides, especially ZnS (zinc blende or sphalerite) and HgS (cinnabar). Overall abundance in the crust are low. Zinc is an important element of life Cd and Hg are not essential and are very toxic. 

Among the oxides and sulphides, only CdO adopts the octahedral rock salt structure found with group 2 element, although the solid is normally very deficient in oxygen and the electrons not used in bonding give rise to metallic properties. ZnO and ZnS are prototypes of the tetrahedrally coordinated wurtzite and zinc blende (or sphalerite) structures in fact, ZnS can adopt either structure, as can CdS and CdSe. HgO and HgS have chain structures with linear two-coordination of Hg. 

ZnS, zinc blende or sphalerite, is the most common ore of zinc, but it is also foimd in a rarer mineral, wurtzite, which is the more stable at high temperatures. These minerals are important archetypal structures found in many other AB compounds that are essentially nonionic and these structures bear the names of the respective minerals. In both, each Zn is tetrahedrally coordinated by four S and each S is coordinated tetrahedrally by four Zn. The stractures differ only in the type... 

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