Wurtzite structure stacking sequence

The sphalerite- and wurtzite-type structures belong to a homeotect structure type set. The layer stacking sequence symbols (triangular nets) of the two structures are ... 

In hexagonal diamond (wurtzite structure) the wrinkled sheets are stacked in an ABABAB sequence, as shown in the Figure 7. Looking down on the stack from above, hexagonal holes can be seen formed by the six-membered carbon rings. The crystal has hexagonal symmetry about this axis, hence the name hexagonal diamond, or wurtzitic carbon. 

The way in which these materials change their structures as the anion to cation ratio is varied is of interest. The structures are all variants of the hexagonal wurtzite structure of AIN in which we have alternate sheets of A1 and N atoms packed normal to the hexagonal c-axis. The stacking sequence can be represented by drawing the atom positions on the (110) planes, as all possible atom sites lie on such planes. In... 

Bulk CdS possesses wurtzite structure ( 4 type) or zincblende structure ( 3 type). Both phases are formed by stacking of close-packed planes of cadmium and sulfur atoms. Hexagonal wurtzite structure can be represented as the periodic sequence AB AB AB... of closed-packed planes. Cubic zincblende is a sequence ABCABC... of closed-packed planes. For both structures the tetrahedral surrounding of both elements, cadmium and sulfur, takes place. According to the available literature data X-ray diffraction patterns of nanostructured CdS films and powders synthesized by different methods have similar features. Analysis of these features shows that the atomic structure of CdS nanoparticles differs from that of the bulk material. 

All of the above diamond-like structures were based on the basic fee lattice. It is also possible for sp bonded compounds to form hep-like structures. Consider the stacking sequence AABBAABB. Carbon stacked in this sequence is known as lonsdaliete or hexagonal diamond and is found in meteorites. The structure (space group PS /mme) is similar to the wurtzite structure shown in Figure 5.10 except all of the atoms are the same. 

It is well known that the equilibrium crystal structure of AlN is wurtzite (2H). 2H-A1N is comprised of a series of Al—N bilayers with the stacking sequence (ABABAB...) along the [0001] direction as shown in Figure 4.1a. The two bilayers, A and B, are identical except for their positions within the (0001) plane. 

Both GaN and AlN crystallize, in equilibrium, in the wurtzite structure, which exhibits an ABAB stacking sequence. 6H-SiC, however, exhibits a ABCACB stacking sequence, which is exposed to GaN nucleating on the (1100) surface. 

Three types of BSFs have been identified in the wurtzite structure the intrinsic fi-type with stacking sequence ABABCBCBC, the intrinsic f2-type with stacking sequence ABABCACA, and the extrinsic E type ABABCABAB. These BSE configurations are depicted in Figure 11.12a-c. Zakharov et al. [46] reported the existence of another type of BSE, namely, a double I sequence stacking fault in a-plane GaN grown on SiC. 

Figure 11.12 Types of intrinsic (/) and extrinsic (E) BSF types in the wurtzite structure showing the change of stacking sequence of the tetrahedrons drawn around the N-atoms h, nd 1 (cf Color Plate XXXIII).

Figure 32. The wurtzite type structure of a-BeO, space group Ptjmc. The three-dimensional network of condensed Be04-tetrabedra is outlined. The stacking of these tetrahedra has the sequence AB, AB. The corresponding stacking ABC, ABC is known to occur for the zinc blende (sphalerite) structure (Fig. 3).

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