ASSOCIATION OF BROAD ICOSAHEDRAL RAMAN BANDS WITH SUBSTITUTIONAL DISORDER IN SIB3 AND BORON-CARBIDE

The structure of silicon boride, SiB3, is based on 12-atom, boron-rich icosahedra in which silicon atoms substitute for some boron atoms. Ra man bands associated with vibrations of icosahedral atoms in SiB3 are quite broad, reflecting this substitutional disorder. Comparing the Ra man spectra of other icosahedral borides with SiB3, only boron carbide s have similarly broad icosahedral Raman bands. The direct correlation of broad icosahedral Raman bands with substitutional disorder support s the proposition that carbon atoms replace icosahedral boron atoms in boron carbides of all compositions.