Polymorphism zinc sulfide

Unit cells of these two structures are shown in Figure 1.37 and Figure 1.38, respectively. They are named after two different naturally occurring mineral forms of zinc sulfide. Zinc blende is often contaminated by iron, making it very dark in colour and thus lending it the name of Black Jack . Structures of the same element or compound that differ only in their atomic arrangements are termed polymorphs. 

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. 

Other AZ stmcture types include cesium chloride, CsCl (Fig. 3.11) two polymorphs of zinc sulfide-wurtzite and zinc blende and NiAs. Although these stmcture t) pes are... 

The zinc blende lattice Is named after its parent compound, ZnS. Zinc sulfide also exists in a different structure known as the wurtzite lattice. Molecules that can exist in more than one type of crystalline form exhibit polymorphism. The wurtzite lattice is comprised of one type of ion forming a hexagonal closest-packed unit cell, with the other type of ion occupying half of the tetrahedral holes. The following molecules can assume the wurtzite lattice ZnO, ZnS, ZnSe, ZnTe, BeO, Agl, CdS, MnS, SiC, AIN, and NH4F. Both types of lattices consist of corner-shared tetrahedrons, but the tetrahedrons in wurtzite are canted in alternating layers. 

Zinc sulfide, ZnS, crystallizes in either of two structures. The zinc sulfide mineral having cubic structure is called zinc blende or sphalerite. Zinc sulfide also exists as hexagonal crystals. (The mineral is called wurtzite.) A sohd substance that can occur in more than one crystal structure is said to be polymorphic. We will discuss only the zinc blende structure (cubic ZnS). 

Sphalerite (zinc blende) is the cubic polymorph of zinc sulfide, ZnS, a II-VI semiconductor. The sulfur atoms form an fee array and the zinc atoms fill half of the... 

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