Vibrational spectra of transition metal phosphosilicides MSi4P4 (M = Fe, Ru, Os)

MSi4P4 compounds (M = Fe, Ru, Os) were studied at 300 K by Raman and IR spe ctroscopy. The low symmetry and the absence of a center of inversion were c onfirmed. The low-wavenumber modes are downshifted after substitution of Ru and Os for Fe, These modes were assigned to relative motions of octahedra and tetrahedra (SiP4 or PSi4) units. The upshift of high-energy modes was r elated to electronic transfer between the metal and the Si-P host lattice a nd to steric effects due to the atomic size increase from Fe to Os. Copyrig ht (C) 1999 John Wiley & Sons, Ltd.