Electrical properties band structure

Although the band model explains well various electronic properties of metal oxides, there are also systems where it fails, presumably because of neglecting electronic correlations within the solid. Therefore, J. B. Good-enough presented alternative criteria derived from the crystal structure, symmetry of orbitals and type of chemical bonding between metal and oxygen. This semiempirical model elucidates and predicts electrical properties of simple oxides and also of more complicated oxidic materials, such as bronzes, spinels, perowskites, etc. 

Ratnayake, C. K., Oh, C. S., and Henry, M. P. (2000). Characteristics of particle-loaded monolithic sol-gel columns for capillary electrochromatography I. Structural, electrical and band-broadening properties. /. Chromatogr. A 887, 277-285. 

The influence of pyrolysis conditions on the structure, morphology, electrical properties, and electrochemical behavior has been investigated. Raman spectroscopy shows that characteristic sp carbon bands form from the pyrolysis treatments. The electrochemical properties for a few of the electrode systems have been reported and, for the most part. 

The electrical properties of any material are a result of the material s electronic structure. The presumption that CPs form bands through extensive molecular obital overlap leads to the assumption that their electronic properties can be explained by band theory. With such an approach, the bands and their electronic population are the chief determinants of whether or not a material is conductive. Here, materials are classified as one of three types shown in Scheme 2, being metals, semiconductors, or insulators. Metals are materials that possess partially-filled bands, and this characteristic is the key factor leading to the conductive nature of this class of materials. Semiconductors, on the other hand, have filled (valence bands) and unfilled (conduction bands) bands that are separated by a range of forbidden energies (known as the band gap ). The conduction band can be populated, at the expense of the valence band, by exciting electrons (thermally and/or photochemically) across this band gap. Insulators possess a band structure similar to semiconductors except here the band gap is much larger and inaccessible under the environmental conditions employed. 

As early as 1943, Sommer (101) reported the existence of a stoichiometric compound CsAu, exhibiting nonmetallic properties. Later reports (53, 102, 103,123) confirmed its existence and described the crystal structure, as well as the electrical and optical properties of this compound. The lattice constant of its CsCl-type structure is reported (103) to be 4.263 0.001 A. Band structure calculations are consistent with observed experimental results that the material is a semiconductor with a band gap of 2.6 eV (102). The phase diagram of the Cs-Au system shows the existence of a discrete CsAu phase (32) of melting point 590°C and a very narrow range of homogeneity (42). 

The electronic properties are also modified by polymerization. Experimentally, the band gap decreases to less than 1.2 eV in the low-pressure orthorhombic phase [65], and experiments [66,88,108] and calculations [80,109-111] agree that the band gap should decrease with an increasing number of intermolecular bonds. (We note the possible exception of the high-pressure polymerized orthorhombic phase, as discussed above.) Calculations [85, 111] show that the rhombohedral phase should have a more three-dimensional band structure than the orthorhombic phase but still be a semiconductor. However, recent measurements by Makarova et al. [88] showed that oriented samples of the rhombohedral phase had an extremely large electrical anisotropy, larger than that of single-crys-... 

The one-electron band structure of organic conductors is typical of molecular solids with a narrow bandwidth. In particular, the bandwidth W is significantly smaller than the on-site Coulomb repulsion U, in general (see also Chapter 2), so that the electrical properties of these conductors are strongly influenced by electron-electron interactions. 

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