Elaboration, Rietveld refinements and vibrational spectroscopic study of Na1-xKxCaPb3(PO4)3 lacunar apatites (0 < x < 1)

• 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 P6(3)/m (No. 176). Rietveld refinements showed that around 90% of Pb2+ cations are located in the (6h) sites, the left amount of Pb2+ cations are located in the (4f) sites; 27-31% of Ca2+ cations are located in the (6h) sites, the left amount of Ca2+ 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 Pb2+/Ca2+ 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 Pb2+/Ca2+ 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.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Multidisciplinär geovetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geosciences, Multidisciplinary (hsv//eng)

Keyword

Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics

Geovetenskap med inriktning mot mineralogi, petrologi och tektonik

Publication and Content Type

ref (subject category)

art (subject category)