Vibrational spectra of double diphosphates CsLnP2O7 (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 factor 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 compounds fit the observed results. Non-coincidences observed between most infrared and Raman bands confirmed that these materials possess the centrosymmetric 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 influence of the cation Ln(3+) on the P-O-P bridge angle. The POP angle values were estimated using the Lazarev's relationship. (C) 2001 Elsevier Science B.V. All rights reserved.