Binary oxides electronic band structures

Electronic Band Structures of Binary Oxides Used as Transparent... 

As we have seen, two binary oxides - MgO in sodium chloride structure and Ti02 in rutile structure (see Chap. 2 for descriptions of these structures) - differ significantly in the character of chemical bonding, which is due to the electron-density distribution being much different in them. We discuss now the differences in the band structures of these crystals. 

The electronic structures of both compounds have been well studied experimentally. The experimental data show that the MgO crystal is a wide-bandgap insulator Eg = 7.8 eV) titanium dioxide Ti02 in the rutile structure is a semiconductor with an experimental bandgap of approximately 3 eV. These differences are reproduced in the band strucrure of these two binary oxides, calculated in [623] by HF and LDA LCAO methods and shown in Figures 9.5 and 9.6, respectively. The details of the AO basis-set choice and BZ summation can be found in [623]. 

In the first half of this book, chemical stability, reactivity, structural features, and chemical bonding including band calculation of the rare earth oxides, have been examined from the viewpoints of the fundamental characterization and appearance mechanism of the properties. Particularly, further development of high resolution electron microscopy (HREM) and quantum band calculation will be of great aid for us to understand the unique characteristics of binary rare earth oxides from both the experimental and theoretical approaches. In addition, physical and chemical properties of the rare earth oxides such as electrical, magnetic, optical, and diffusion properties are also analyzed in details, leading to find relationships between basic science and applications in several functional materials. 

The synthesis of lanthanide and actinide compounds is the topic of a book edited by Meyer and Morss (1991). Topics that relate to halides, with the author(s) in brackets, include Lanthanide fluorides [B.G. Muller], Actinide fluorides [N.P. Freestone], Binary lanthanide(III) halides, RX3, X = Cl, Br, and I [G. Meyer], Complex lan-thanide(III) chlorides, bromides and iodides [G. Meyer], Conproportionation routes to reduced lanthanide halides [J.D. Corbett], and Action of alkali metals on lanthanide(III) halides an alternative to the conproportionation route to reduced lanthanide halides [G. Meyer and T. Schleid]. Meyer and Meyer (1992) reviewed lanthanide halides in which the valence of the lanthanide was considered unusual, with unusual being defined as compounds in which the localized valence of an atom differs from its oxidation number. A metallic halide such as Lalj [oxidation number (0)= -1-2 valence (V)= -l-3, since the 5d electron is delocalized in the conduction band] or a semiconducting halide such as PrjBtj (O = -t- 2.5 V = -I- 3) is unusual by this definition, but Tmlj (O = -1-2 V = +2) is not. In this review synthesis, properties, and calculated electronic structures are considered with emphasis on praseodymium halides and hydrogen intercalation into lanthanide dihalides and monohalides . 

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