INTERBAND CRITICAL-POINTS OF SOME ICOSAHEDRAL BORON-RICH SOLIDS

The complex dielectric functions of beta-rhombohedral boron, of boron carbide with compositions between B4.23C and B10.37C and YB66, mere me asured between about 2.5 and 9.5 eV. Similarities of the electronic st ructures probably due to the icosahedra are indicated by obvious quali tative similarities of the spcetra, Numerous critical points have been determined and confirm the dense sequence of energy bands, For beta-r hombohedral boron the critical points are compatible with the combined density of states maxima derived from cluster calculations by K. Shir ai and H. Nakamatsu (1994, in ''Proc. 11th Int. Symp. Boron, Borides a nd Related Comp, Tsukuba, 1993,'' JJAP Series 10, p. 70), Otherwise no satisfactory correlation with theoretical band structure calculations is possible, In the case of boron carbide the critical points art the same within the whole homogeneity range, while the values of the diel ectric function at higher energies indicate composition-dependent dens ities of states, which are correlated with the density of B-12 icosahe dra. (C) 1997 Academic Press.