Figure 38. X-ray diffractograms of two CoAl2O4 samples prepared by multicomponent (a) and single-source (b) precursor routes. Reprinted with permission from [244], F. Meyer et al., J. Mater. Chem. 9, 1755 (1999). © 1999, Royal Society of Chemistry.

Similarly, nanocrystalline CuAl2O4 and NiAl2O4 could be obtained by processing [CuAl2(OBu()8] and [NiAl2(OBu')8], respectively.

Similarly, zinc aluminate (ZnAl2O4), a well-known wide bandgap semiconductor with a spinel structure, was prepared by the sol-gel processing of the bimetallic precursor shown in Figure 39. Recent investigations of ZnM2O4 (M = Al, Ga) compounds have shown these systems to be new transparent and conductive materials [552]. The optical bandgap of polycrystalline ZnAl2O4 (3.8 eV) indicates the material to be transparent for light with a wavelength larger than 320 nm. Thus it can be utilized for UV-photoelectronic devices. Moreover, the ZnAl2O4 spinel is useful in many catalytic reactions, such as cracking, dehydration, hydrogenation, and dehydrogenation [553]. The XRD pattern of the sample calcined at 400 °C shows zinc aluminate (Gahnite) to be the only crystalline phase. This is the lowest reported temperature for the formation of single-phase crystalline ZnAl2O4. The crystallite size calculated from the line shape analysis of the diffraction peaks showed a log normal grain growth with increasing calcination temperature (Fig. 40). The above observations are in accordance with the TEM observations showing a systematic crystal growth (Fig. 41).

Figure 39. Molecular structure of [ZnAl2(OBu')8

Figure 37. Molecular structure of [CoAl2(OBu')8].

Figure 39. Molecular structure of [ZnAl2(OBu')8


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