Spectre vibrationnel des composés du type Ba3(XO4)2 et Sr3(XO4)2 (Xv = P, As, V, Cr, Mn)

A systematic study has been made of the Raman and i.r. spectra of the isomorphic ortho-phosphates, -arsenates and -vanadates of barium and strontium, and of the i.r. spectra of the corresponding chromates (V) and manganates (V). The spectra are consistent with the C3v local symmetry of the anion, and with the D3d symmetry of the rhombohedral unit cell. Out of a total of 12 predicted internal frequencies (six Raman-, and six i.r.-active, with no coincidence), six have been observed in the Raman spectrum, whereas this number reduces to four or five in the i.r. spectrum, as a consequence of the superposition of strong and weak bands in the same spectral region. The external frequencies are more or less sensitive to the nature of both cation and anion. © 1972.