Structure types zinc blend

GasSeg Black aggregate, red when ground. Fairly hard and brittle. M.p. 1020°C, d (x-ray) 5.203. B3 structure type (zinc blende). 

All three compounds crystallize in B3 structure type (zinc blende). 

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 four other carbon atoms by sp3 ct bonds in a strain-free tetrahedral array, Fig. 2A. The crystal structure 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 em 3. 

Among compounds of this type, zinc blende and wurtzite structures often occur viz, (BeS, BeSe, BeTe, ZnS, ZnSe, ZnTe, CdS, CdSe, GdTe, HgS, HgSe, HgTe, MgTe, AIN, AlP, AlAs, AlSb, GaP, GaAs, GaSb). In these structures where the coordination number is 4, the bond is predominantly covalent, as we have seen previously. 

AX-type structures which include the rock salt structure, CsCl, zinc blende, and wurtzite structures. The rock salt structure (Fig. 3.la), named after... 

The sodium chloride (NaCl also called the rock salt structure) and zinc blende (ZnS) structures are based on a face-centered cubic lattice. In both structures the anions sit on the lattice points that lie on the corners and faces of the unit cell, but the two-atom motif is slightly different for the two structures. In NaCl the Na ions are displaced from the CF ions along the edge of the unit cell, whereas in ZnS the Zn ions are displaced from the ions along the body diagonal of the unit cell. This difference leads to different coordination numbers. In sodium chloride, each cation and each anion are surrounded by six ions of the opposite type, leading to an octahedral coordination environment. In zinc blende, each cation and... 

One particular type of cubic structure, the zinc blende structure found in several important compound ceramic semiconductors such as GaAs and InP, has been known to exhibit a particular type of composition hardness anisotropy first noted more than 40 years ago when it was christened hardness polarity. This effect is seen on (111) and (ITT) faces of the group Ill-group V ceramics, of which GaAs is the most investigated. The hardness difference is ascribed initially to the fact that these two planes are formed either by... 

The bulk crystal structure of zinc-blende-type III-V semiconductors is cubic, that is, of point group symmetry (Section 13.2). Such crystals are optically isotropic in first-order approximation, that is, if symmetry reducing effects, such as finite k-vector electric fields and other effects are neglected [138]. Then the RAS signal should originate from the surface that is anisotropic due to the termination of crystal periodicity and due to the surface reconstraction [127-129]. Apart from the structural anisotropy and related effects such as strain, the surface electric field accompanied by the band bending will modify electronic eigenstates and induce an optical anisotropy as well. 

Betyllium, because of its small size, almost invariably has a coordination number of 4. This is important in analytical chemistry since it ensures that edta, which coordinates strongly to Mg, Ca (and Al), does not chelate Be appreciably. BeO has the wurtzite (ZnS, p. 1209) structure whilst the other Be chalcogenides adopt the zinc blende modification. BeF2 has the cristobalite (SiOi, p. 342) structure and has only a vety low electrical conductivity when fused. Be2C and Be2B have extended lattices of the antifluorite type with 4-coordinate Be and 8-coordinate C or B. Be2Si04 has the phenacite structure (p. 347) in which both Be and Si... 

The predominantly ionic alkali metal sulfides M2S (Li, Na, K, Rb, Cs) adopt the antifluorite structure (p. 118) in which each S atom is surrounded by a cube of 8 M and each M by a tetrahedron of S. The alkaline earth sulfides MS (Mg, Ca, Sr, Ba) adopt the NaCl-type 6 6 structure (p. 242) as do many other monosulfides of rather less basic metals (M = Pb, Mn, La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Th, U, Pu). However, many metals in the later transition element groups show substantial trends to increasing covalency leading either to lower coordination numbers or to layer-lattice structures. Thus MS (Be, Zn, Cd, Hg) adopt the 4 4 zinc blende structure (p. 1210) and ZnS, CdS and MnS also crystallize in the 4 4 wurtzite modification (p. 1210). In both of these structures both M and S are tetrahedrally coordinated, whereas PtS, which also has 4 4... 

The principal compounds in this category are the monochalacogenides, which are formed by all three metals. It is a notable indication of the stability of tetrahedral coordination for the elements of Group 12 that, of the 12 compounds of this type, only CdO, HgO and HgS adopt a structure other than wurtzite or zinc blende (both of which involve tetrahedral coordination of the cation — see below). CdO adopts the 6-coordinate rock-salt structure HgO features zigzag chains of almost linear O-Hg-0 units and HgS exists in both a zinc-blende form and in a rock-salt form. 

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). 

The zinc blende type is unknown for truly ionic compounds because there exists no pair of ions having the appropriate radius ratio. However, it is well known for compounds with considerable covalent bonding even when the zinc blende type is not to be expected according to the relative sizes of the atoms in the sense of the above-mentioned considerations. Examples are CuCl, Agl, ZnS, SiC, and GaAs. We focus in more detail on this structure type in Chapter 12. 

When the positions of cations and anions are interchanged, the same structure types result for the CsCl, NaCl and zinc blende type. In the case of the fluorite type the interchange also involves an interchange of the coordination numbers, i.e. the anions obtain coordination number 8 and the cations 4. This structure type sometimes is called anti-fluorite type it is known for the alkali metal oxides (Li20,..., Rb20). 

Of the numerous ternary and polynary diamond-like compounds we deal only with those that can be considered as superstructures of zinc blende. A superstructure is a structure that, while having the same structural principle, has an enlarged unit cell. When the unit cell of zinc blende is doubled in one direction (c axis), different kinds of atoms can occupy the doubled number of atomic positions. All the structure types listed in Fig. 12.8 have the tetrahedral coordination of all atoms in common, except for the variants with certain vacant positions. 

The relation between diamond and zinc blende shown above is a formal view. The substitution of carbon atoms by zinc and sulfur atoms cannot be performed in reality. The distortion of the NiAs structure according to Fig. 18.4, however, can actually be performed. This happens during phase transitions (Section 18.4). For example, MnAs exhibits this kind of phase transition at 125 °C (NiAs type above 125 °C, second-order phase transition another transition takes place at 45 °C, cf. p. 238). 

Vaughey J. T., O Hara J., Thackeray M. M., Intermetallic insertion electrodes with a zinc blende-type structure for Li Batteries A study of LixInSb (0 <= x <= 3), Electrochem. and Solid State Lett., (2000) 3 (1), 13-16. 

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. 

Yellow to orange crystal occurs as two polymorphs, hexagonal alpha form and cubic beta form exhibits stable wurtzite structure at lower temperature, and zinc blende type structure at higher temperatures the beta form converts to alpha form when heated at 750°C in sulfur atmosphere sublimes at 980°C practically insoluble in water (1.3 mg/L at 20°C) Ksp 3.6x10-29 dissolves in dilute mineral acids on heating or concentrated acids at ordinary temperatures (decomposes with liberation of H2S). 

AB structures. The five principal structures of AB type compounds are rocksalt (Bl), CsCl (B2), zinc blende (B3), wurtzite (B4) and NiAs (B8) and these are shown in Fig. 1.5. In the first four of the structures, the cation and anion sublattices are entirely equivalent and the coordination geometry around the cation and anion is the same. The rocksalt NaCl) structure is exhibited by a large number of AB type compounds. The structure (Fig. 1.5) may be thought of as consisting of two interpenetrating... 

Fig. 3.4 The Phiilips-Van Vechten structure map ( c, ) for the sp-valent octet AB compounds. The four-fold coordinated zinc blende and wurtzite structure types are separated from the six-fold coordinated NaCI structure type by the straight line corresponding to the degree of ionicity a = 0.785. (After Phillips and Van Vechten (1969).)...

Where there is very strong polarization, such as in hydrogen compounds, it can happen that molecules of the type AB no longer have coordinated structures this is so in hydrogen compounds such as HG1, HBr, HI and H20. The strong polarization in these molecules would disappear if they were arranged in a coordination lattice of the NaCl or zinc-blende type. 

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