Polycrystalline Pb6Ca2Na2(PO4)6 was obtained via a solid-state reaction. It was characterized by using infra-red spectrometry and X-ray diffraction, its structure was refined by using the Rietveld method. It crystallizes in the hexagonal system (s.g. P63/m, a = 0.9658nm and c = 0.7081nm) and presents a lacunary structure stabilized by the electron lone pair of Pb(II) ions. At 720K, an order–disorder phase transition probably of first order was observed either in conductivity or X-ray diffraction studies versus temperature. Electric conductivity was dominated by the mobility of Na in the tunnels.

Structure and Ionic Conductivity of the Lacunary Apatite Pb6Ca2Na2(PO4)6. T.Naddari, H.El Feki, J.M.Savariault, P.Salles, A.Ben Salah: Solid State Ionics, 2003, 158[1-2], 157-66

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