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

The rubidium double diphosphates RbLnP(2)O(7) (Ln = Dy, Ho, Y, Er, Tin, Yb) have been conjointly studied by X-ray diffraction and vibrational spectros copy. The infrared and Raman spectra of these compounds were established an d 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. The similarities between the vibrational spectra of RbLnP(2)O(7) show that they are isostru ctural. Non-coincidences are observed., between most infrared and Raman ban ds confirm a centrosymetric structure for these compounds. The vibrational spectra point to a beat POP bridge angle in all these materials. The slight shift of the frequencies of v(as)(POP) and v(s)(POP) on the vibrational sp ectra is due to the influence of the cation Ln(3+) on the POP bridge angle, The POP angle values were estimated using the Lazarev's relationship. (C) 2001 Elsevier Science B.V. All rights reserved.