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 language | English |
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Pages (from-to) | 1199-1205 |
Number of pages | 7 |
Journal | Journal of Physics and Chemistry of Solids |
Volume | 72 |
Issue number | 11 |
DOIs | |
State | Published - Nov 2011 |
Externally published | Yes |
Funding
The authors are grateful to the Swedish Research Council and the Swedish International Development Co-operation Agency (Sida) for the financial grant (MENA) offered in support of this work.
Funders | Funder number |
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MENA | |
Swedish International Development Co-operation Agency | |
Vetenskapsrådet |
Keywords
- C. Raman and infrared spectroscopies
- C. X-ray diffraction