Vibrational spectra of double diphosphates CsLnP(2)O(7) (Ln=Gd, Tb, Dy, Ho, Y, Er, Tm, Yb)

Raman and infrared absorption spectra of diphosphates CsLnP(2)O(7) (Ln = Gd , Tb, Dy, Ho, Y, Er, Tm, Yb) have been recorded and interpreted using facto r group analysis. The spectral features predicted with factor group arising from the X-ray crystallographic space group P2(1)/c (C-2h(5)) for these co mpounds fit the observed results. Non-coincidences observed between most in frared and Raman bands confirmed that these materials possess the centrosym metric structure. The similarities between the vibrational spectra of CsLnP (2)O(7) suggested that they are isostructural. The shift of the frequencies v(as) (POP) and v(s) (POP) on the vibrational spectra is due to the influe nce of the cation Ln(3+) on the P-O-P bridge angle. The POP angle values we re estimated using the Lazarev's relationship. (C) 2001 Elsevier Science B. V. All rights reserved.