Electronics, pnictides

Among binary transition-metal pnictides, only the first-row transition-metal phosphides have been analysed by XPS extensively, whereas arsenides and antimonides have been barely studied [51-61]. Table 2 reveals some general trends in the P 2p3/2 BEs for various first-row transition-metal monophosphides, as well as some metaland phosphorus-rich members forming for a given transition metal. Deviations of as much as a few tenths of an electron volt are seen in the BEs for some compounds measured multiple times by different investigators (e.g., MnP), but these... 

B. Electronic Features and Structural Principles of Molecular Main Group Metal Pnictides... 

The electrostatically favored cation (Li) and anion (RE) arrangement implies the presence of two different E-, Si- and Li sorts, which has been established by solution and solid-state NMR spectroscopy. The electronic structures of the mixed-valent pnictides 10 and 11 have been simply described as electron-deficient clusters with delocalized framework electrons. Formally the latter consist of two low-valent anediyl moieties RE and eight andiides (RE)2- (E = P, As). The relatively large E-E distances of >4 A exclude the occurrence of localized E-E bonds. However, delocalization of the cluster valence electrons is achieved without Li-Li bonds via Li-mediated multiple bonding. Evidence for this has been seen in the NMR spectra (31P, 7Li, 29Si), which are in accordance with the electron delocalization model (see later discussion). 

The general shape of these curves at least for pnictides up to AnAs indicates clearly that the metallie bond is dominated by the electronic structure of the actinide atom. In the further discussion of this chapter (and in Chaps. C-F) it will be made clear that the shape is explained, contrarily to Zachariasen s hypothesis, by means of the f participation in the bond. 

From a chemical point of view, 5 f electrons will participate in the chemical bond as evidenced by their very high melting points when one compares them with the ones of lanthanide pnictides and chalcogenides. 

Pnictide-transition metal bonds are essentially covalent coordinate, in which the pnictide provides the electrons. However, this simple picture does not account for all the structural data now available. The consensus view is that three factors are involved in the ligand contribution to the M—E bond (a) a bonding (Section 14.4.2), (b) n bonding (Section 14.4.3), and (c) steric factors (Section 14.3). The effect of the metal will not be discussed here, except insofar as individual complexes are used as examples. 

Though all TiP-type representatives are metallic their structure indicates a striving towards bond saturation. Only Ti-group pnictides are known with this structure, hence the cations carry one excess valence electron. As is needed to bind this excess d electron, the structure indeed shows cation pairs (Fig. 48d), but obviously the actual M—M distances are too long to represent single bonds (2.91 A in TiP, 3.23 A in TiAs and 3.13 A in ZrP). 

There are several materials which exhibit semiconducting behaviour in glassy state and are technologically important for their proven and potential device applications. The most notable of them are the amorphous silicon and a number of chalcogenide and pnictide glasses. In this chapter, we put together briefly the understanding we have of electron transport in such amorphous semiconductors. 

Consider that atoms have a size range of about 1-2 A. Most inorganic solids, with the exception of halides, sulfides (and other pnictides), are based upon the oxygen atom, i.e.- oxide = O", whose atomic radius does not change even when sulfates, phosphates and silicates are formed. Oxide has an atomic diameter of 1.5 A or 0.15 nm. = 0.00015 (om. Nanoparticles are clumps of 1000 to 10,000 atoms. The latter would be a particle of 0.15 (om. in diameter. They can be metal oxides, semiconductors, or metals with novel properties useful for electronic, optical, magnetic and/or catalytic uses. 

Metal pnictides are best represented by the 13-15 compounds (e.g., GaAs), which are well known for their electronic and optoelectronic applications. Molecular precursor approach to the preparation of these materials has been investigated and reviewed by Maury and Cowley,who have also actively contributed to the field. 

Antimony, the fourth member of the pnictide family, is the only one to exhibit substantial natural isotope variability. The electronic structure of antimony is... 

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