Wurtzite lattice

Cadmium sulfide [68859-25-6], CdS, Mr 144.48, occurs as greenockite or cadmium-blende in several natural deposits, which are, however, of no importance as pigments. The mineral crystallizes hexagonally in the wurtzite lattice (a-form). 

The luminescent properties can be influenced by the nature of the activators and coactivators, their concentrations, the composition of the flux, and the firing conditions. In addition, specific substitution of zinc or sulfur in the host lattice by cadmium or selenium is possible, which also influences the luminescent properties. Zinc sulfide is dimorphic and crystallizes below 1020 °C in the cubic zinc-blende structure and above that temperature in the hexagonal wurtzite lattice. When the zinc is replaced by cadmium, the transition temperature is lowered so that the hexagonal modification predominates. Substitution of sulfur by selenium, on the other hand, stabilizes the zinc-blende lattice. 

Impurity ions in wurtzite lattices are described by the same expressions for P2, and P3c, with a numerically insignificant difference in P3o. These expressions are only quantitatively accurate in the dilute limit, but many of the doped nanocrystals discussed in this chapter fall in this limit. The reader is referred to Ref. 42 for a generalized treatment of the problem. Figure 2(b) plots the probabilities calculated from Eq. 4a-d as a function of impurity concentration. The fraction of dopants having at least one nearest-neighbor dopant is quite high even at moderate impurity concentrations (<5%). Needless to say, whereas purification to ensure size uniformity is possible (size-selective precipitation), no purification method has yet been developed for ensuring uniform dopant concentrations in an ensemble of nanocrystals. 

Fig. 1.16. Diffusion paths accessible to oxygen interstitials on the wurtzite lattice...

The wurtzite lattice of ZnO and its low-index surfaces are shown in Fig. 4.5. The basic low index surface terminations are (0001), (0001), (1010), and (1120). The (0001) and (0001) represent the zinc and oxygen-terminated surfaces of the polar 0001 direction, which corresponds to the 111 direction of the cubic zincblende lattice. In contrast to the polar (100) and (100) surfaces of the zincblende lattice, the surfaces with threefold symmetry (111)... 

All the normal oxides have the sodium chloride structure, except BeO which has a wurtzite lattice (4 4 co-ordination). The heats of formation are very large (135-150 kcal/mole). BeO is unreactive to water even the large heat of hydration of Be is evidently insufficient to overcome the stabilising effect of the high lattice energy. MgO reacts with water only when prepared at a low temperature, but the alkaline earth oxides slake readily ... 

The sulphides M2S3 are all made by direct combination of the elements. But GaS is also known and has an unusual layer lattice containing Ga2 ions (Hahn and Frank, 1955). The nitride GaN,unreactive to water and acids, is made by heating gallium in ammonia at 1000° the corresponding indium compound is best made by heating (NH4)3lnFg. Both have the wurtzite lattice. 

A thin film of TIN, formed from Tl+N2 by reaction during cathode sputtering, has the hexagonal, wurtzite lattice.587... 

CdTe, HgS, HgSe and HgTe. Each binary compound (including zinc blende) is an intrinsic semiconductor. The wurtzite lattice is also important in semiconducting materials ZnO, CdSe and InN are examples of compounds adopting this structure. 

BerylUum oxide, BeO, is formed by ignition of Be or its compounds in O2. It is an insoluble white solid which adopts a wurtzite lattice (see Figure 5.20). The oxides of the other group 2 metals are usually prepared by thermal decomposition of the corresponding carbonate (equation... 

Of the group 13 metals, only A1 reacts directly with N2 (at 1020K) to form a nitride AIN has a wurtzite lattice and is hydrolysed to NH3 by hot dilute alkali. Gallium and indium nitrides also crystallize with the wurtzite structure, and are more reactive than their B or A1 counterparts. The importance of the group 13 metal nitrides, and of the related... 

Fig. 25. Arrangement of the hexagonal Wurtzite lattice corresponding to the presence of stacking faults, with 3 or 4 planes presenting the cubic blende modification, (from [175]) With permission of Elsevier...

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