Electron deficiency boron-rich solid

Table 8 shows that, for a-rhombohedral boron, p-rhombohedral boron and boron carbide, the electron deficiencies determined by electronic band structure calculations are correlated with the densities of defects in the structures. Since calculations of the electronic properties of defects in icosahedral boron-rich solids are missing, the following assumptions (202) were made in accordance with general results obtained on defects in semiconductors. 

The shown possibility to exactly explain the structural defects of some icosahedral boron-rich solids by the electron deficiency considerably raises the estimation of the theoretical band structure calculations, hitherto essentially based on the more or less significant shortage of agreement with experimental results. Calculations of the electronic orbitals of defects are desirable to improve the quantitative understanding of the different defects. It seems that, on one hand, the electron deficiency is the driving force for the generation of structural defects in the icosahedral boron-rich solids in general, and on the other hand, the influence of these defects on the electronic properties is a main reason for their peculiar properties. 

The a-rhombohedral structure of elemental boron has an electron deficiency that can be reduced by the incorporation of interstitial atoms in structural voids. Filling these voids with atoms can result in cross-linking of the boron icosahedra which is realized for example in the structures of B4C (B12C3), B12P2, B4N, or boron rich boron suboxides (see Fig. 11) and can contribute to a significant increase of the rigidity of the solid state structure. 

---