Interstitial electron model

The description of metal bonding by interstitial electrons was given in 1972. In the interstitial electron model, atoms in metals shed some of their valence electrons, which occupy interstitial holes in the metal ion lattice. Not all of the valence electrons are in the interstices. The more electrons that are removed from the atoms, the more electronegative the cations become and the less they tend to donate further electrons to the interstices. Thus some valence electrons stay behind on the metal ions. How many depends on the atom. 

Figure 2.24. The interstitial spaces in fee and bee lattices (I) The cubic fee lattice with an octahedral and a tetrahedral interstitial site indicated. In the interstitial electron model the valence electrons in fee metals occupy these sites. (II) The cubic bcc lattice a and the types of interstitial sites. The octahedral sites in one of the cube faces are shown as squares in b. The tetrahedral sites (triangles) are closely connected and form rings in the side planes and around the cube ribs as shown in c and d.

Johnson s interstitial electron model has not been used by others, the dominant model for metallic bonding being the band model. Recently the interstitial view was revived because new ab initio calculations (calculated approximations without... 

Discuss the electric and magnetic properties of metals in terms of the interstitial electron model. 

Find the Hume-Rothery criterion (15% rule) of mutual solubility of elementary metals and discuss it in terms of the Johnson interstitial electron model. 

Li, M. and Goddard III, W.A. Interstitial-electron model for lattice dynamics in fee metals. Physical Review B, 40,12155-12163,1989. 

Thermodynamic considerations imply that all crystals must contain a certain number of defects at nonzero temperatures (0 K). Defects are important because they are much more abundant at surfaces than in bulk, and in oxides they are usually responsible for many of the catalytic and chemical properties.15 Bulk defects may be classified either as point defects or as extended defects such as line defects and planar defects. Examples of point defects in crystals are Frenkel (vacancy plus interstitial of the same type) and Schottky (balancing pairs of vacancies) types of defects. On oxide surfaces, the point defects can be cation or anion vacancies or adatoms. Measurements of the electronic structure of a variety of oxide surfaces have shown that the predominant type of defect formed when samples are heated are oxygen vacancies.16 Hence, most of the surface models of... 

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