Raman spectra of CaAs3, EuAs3, SrAs3, BaAs3, and α-EuP3 and the mixed phases, Eusub(1-x)Srsub(x)As3, and Eu(Psub(1-x)Assub(x))3

The Raman spectra of the triarsenides MAs3 (M = Ca, Eu, Sr, Ba), α-EuP3 and of solid solutions, Eusub(1-x)Srsub(x)As3 and Eu(Psub(1-x)Assub(x))3, are measured. A great similarity between the phonon spectra and simple scaling relations between the corresponding lattice vibrations of the triarsenides reflect the strong structural relationships between the monoclinic MAs3 and slightly distorted triclinic CaAs3 and suggest very similar vibrational eigenvectors. The Raman spectra of the solid solutions, Eusub(1-x)Srsub(x)As3 and Eu(Psub(1-x)Assub(x))3, display a mixed one- and two-mode behaviour. It is shown that the strong coupling between atoms in the puckered As(P) layers reflects itself in the appearance of high-frequency modes associated mainly with vibrations of atoms within the puckered layer, whereas the low-frequency modes are dominated by metal vibrations. (author)