Synthesis and distribution of cations in substituted lead phosphate lacunar apatites

Synthesis of apatites, Pb 7.4Bi 0.3Na 2.3(PO 4) 6 (I), Pb 7.36Bi 0.32Na 2.08Li 0.24(PO 4) 6 (II) and Pb 5.78Bi 0.81Ca 0.60Na 2.81(PO 4) 6 (III), with anion vacancy were carried out during solid state reactions. The three compounds of apatite-type structure crystallize in the hexagonal system, space group P6 3/ m. In every compound, a preferential occupation of the (6h) site by Pb and Bi cations is shown revealing the influence of their lone electronic pair. The introduction of calcium increases the quantity of bismuth in these apatites. Alkaline metals occupy mainly the (4f) site. Infrared spectroscopy is correlated to the bonding scheme. A connection between the cations occupying (4f) sites and the c cell parameters is presented.