title: Elaboration, Rietveld refinements and vibrational spectroscopic study of Na₁-xKxCaPb₃(PO₄)₃ lacunar apatites (0 ⩽ x ⩽ 1).
abstract: Synthesis of apatites, Na1-xKxCaPb3(PO4)3 0 ⩽ x ⩽ 1, with anion vacancy were carried out using solid state reactions. The solid solution of apatite-type structure crystallize in the hexagonal system, space group P63/m (No. 176). Rietveld refinements showed that around 90% of Pb(2+) cations are located in the (6h) sites, the left amount of Pb(2+) cations are located in the (4f) sites; 27-31% of Ca(2+) cations are located in the (6h) sites, the left amount of Ca(2+) cations are located in the (4f) sites. The ninefold coordination sites (4f) are also occupied by the K(+) and Na(+) monovalent ions. The structure can be described as built up from [PO4](3-) tetrahedra and Pb(2+)/Ca(2+) of sixfold coordination cavities (6h positions), which delimit void hexagonal tunnels running along [001]. These tunnels are connected by cations of mixed sites (4f) which are half occupied by Pb(2+)/Ca(2+) 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. Vibrational spectra of all the compositions are similar and 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.
authors: Univ. Hassan 1(er), Laboratoire des Sciences des Matériaux, des Milieux et de la Modélisation (LS3M), 25000 Khouribga, Morocco; Univ. Hassan 1(er), Laboratoire de Chimie et Modélisation Mathématique, 25000 Khouribga, Morocco.
authors: S
authors: S
authors: Lahrich
authors: Univ. Hassan 1(er), Laboratoire de Chimie et Modélisation Mathématique, 25000 Khouribga, Morocco.
authors: M A
authors: MA
authors: Elmhammedi
authors: Univ. Hassan 1(er), Laboratoire des Sciences des Matériaux, des Milieux et de la Modélisation (LS3M), 25000 Khouribga, Morocco. Electronic address: manounb@gmail.com.
authors: B
authors: B
authors: Manoun
authors: Univ. Hassan 1(er), Laboratoire des Sciences des Matériaux, des Milieux et de la Modélisation (LS3M), 25000 Khouribga, Morocco.
authors: Y
authors: Y
authors: Tamraoui
authors: Univ. Hassan 1(er), Laboratoire des Sciences des Matériaux, des Milieux et de la Modélisation (LS3M), 25000 Khouribga, Morocco.
authors: F
authors: F
authors: Mirinioui
authors: Laboratoire de Physico-chimie des Matériaux, FST Errachidia, Morocco.
authors: M
authors: M
authors: Azrour
authors: Department of Earth Sciences, Uppsala University, SE-752 36 Uppsala, Sweden.
authors: P
authors: P
authors: Lazor
mesh_terms: D001031:Apatites / Q000737:chemistry*; D002412:Cations; D018360:Crystallography, X-Ray; D007854:Lead / Q000737:chemistry; D011188:Potassium / Q000737:chemistry; D011208:Powders; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D014732:Vibration
chemical_list: D001031:Apatites; D002412:Cations; D011208:Powders; D007854:Lead; D011188:Potassium
keywords: Lacunar apatite; Na(1−)(x)K(x)CaPb(3)(PO(4))(3); Raman and infrared spectroscopies; Rietveld; X-ray diffraction