Interband transitions and optical phonons of B48Al3C2

The optical absorption edge of B48Al3C2 has been measured. It is decomposed into several interband transitions between 0.97 and 2.5 eV. Additionally, several gap-state-related transitions with energies between 0.45 and 0.96 e V were determined. They are attributed to defects in the structure, whose c haracter is not yet known, The spectra of IR- and Raman-active phonons and their resonance frequencies are presented. According to other icosahedral b oron-rich solids, the phonons can roughly be separated into vibrations of i cosahedra and those of single atoms. The vibrations of the tetrahedrally bo nded All atom are discussed in analogy to the tetrahedral XY4 molecule. (C) 2000 Academic Press.