Rietveld refinements and vibrational spectroscopic studies of Na 1-xKxPb4(PO4)3 lacunar apatites (0≤x≤1)

M. Azrour, M. Azdouz, B. Manoun, R. Essehli, S. Benmokhtar, L. Bih, L. El Ammari, A. Ezzahi, A. Ider, A. Ait Hou

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Abstract

Synthesis of apatites, Na1-xKxPb4(PO 4)3 0≤x≤1, with anion vacancy was carried out using solid state reactions. The solid solution of apatite-type structure crystallizes in the hexagonal system, space group P63/m (No 176). Rietveld refinements showed that 75% of Pb2 cations are located in the (6h) sites; the ninefold coordination sites (4f) are equally occupied by the other 25% lead cations and the K and Na monovalent ions. The structure can be described as built up from [PO4]3- tetrahedra and Pb 2 of sixfold coordination cavities (6h positions), which delimit void hexagonal tunnels running along [0 0 1]. These tunnels are connected by cations of mixed sites (4f) half occupied by Pb2 and half by Na/K mixed cations. The assignment of the observed frequencies in the Raman and infrared spectra is discussed on the basis of a unit cell group analysis and by comparison with other apatites. The Raman modes of all the compositions show some linear shifts of the frequencies as a function of the composition toward lower values due the substitutions of Na by K with a larger radius.

Original languageEnglish
Pages (from-to)1199-1205
Number of pages7
JournalJournal of Physics and Chemistry of Solids
Volume72
Issue number11
DOIs
Publication statusPublished - Nov 2011

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Keywords

  • C. Raman and infrared spectroscopies
  • C. X-ray diffraction

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Cite this

Azrour, M., Azdouz, M., Manoun, B., Essehli, R., Benmokhtar, S., Bih, L., El Ammari, L., Ezzahi, A., Ider, A., & Hou, A. A. (2011). Rietveld refinements and vibrational spectroscopic studies of Na 1-xKxPb4(PO4)3 lacunar apatites (0≤x≤1). Journal of Physics and Chemistry of Solids, 72(11), 1199-1205. https://doi.org/10.1016/j.jpcs.2011.06.013