Rietveld refinement and spectroscopic studies of sodium lead fluoroapatite lacunaire synthesized by hydrothermal method

The structure of NaPb9(PO4)6F(H2O)0.33, isostructural with apatite, was determined by X-ray powder diffraction methods and the result of Rietveld refinement is P63/m, a = 9.76396(8) Å and c = 7.27520(9) Å. The final refinement led to RF = 5.4%, RB = 6.6%. In the tunnel, the water molecule (Ow) and F− ions appear to be located in 2b and 4e sites, with occupancies of 0.028(6) and 0.075(8), respectively. In the M(1) and M(2) sites the occupancies of Pb and Na are 0.282(3)/0.051(3) and 0.467(5)/0.033(5), respectively. The formula assigned to the compound is [Pb3.38(4)Na0.62(4)](1)[Pb5.60(6)Na0.40(6)](2)(PO4)6F0.90(10)(H2O)0.33(7)□0.77(17), where □ = vacancy. 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 fluor and chloroapatite analogs. The result of 31P and 23Na magic angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopies confirmed the structural results.