Synthesis,crystal structure and vibrational spectroscopy studies of the lacunar apatite NaPb2Ca2(PO4)3

Powder napb2ca2(po4)3 lacunar apatite was synthesized by the solid-state reaction method,and its crystal structure was investigated by rietveld analysis. napb2ca2(po4)3 material is hexagonal apatite at room temperature,adopting the space group p63/m (ita no. 176),a=b=9.6075(2)å,c=7.0167(1)å,z=2. rietveld refinements showed that the site 4f is shared by three cations ca,pb and na; while,the 6h is occupied by the pb and na cations. the structure can be described as built up from the po4tetrahedra and the sixfold coordination cavities,which delimit hexagonal tunnels along the c-axis direction. these tunnels are linked by the cations occupying the 4f sites. raman spectroscopy analysis has been carried out. the observed frequencies were assigned and discussed on the basis of unit-cell group analysis and by comparison to other apatite-type materials.