Lattice parameters and cation distribution of solid solutions of calcium and lead hydroxyapatite
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- Verbeeck, R.M.H., Lassuyt, C.J., Heijligers, H.J.M. et al. Calcif Tissue Int (1981) 33: 243. doi:10.1007/BF02409444
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Solid solutions of calcium hydroxyapatite (CaOHA) and lead hydroxyapatite (PbOHA) of the formula Ca10−x Pbx (PO4)6 (OH)2 were prepared by coprecipitation followed by heating at 800°C in a stream of CO2-free water vapor of 1 atm. The samples were apatitic in the range 0<x<6 and contained lead phosphates as a second phase at higher Pb/Ca ratios. Lattice parameters and cation distribution of the apatitic samples were determined by X-ray diffraction. The lattice parameters varied linearly with x in the range considered, whereas all Pb2+ were located in the sixfold position for cations. There was a miscibility gap in the apatite series of solid solutions in the range 1<x<4, whereas apatites in the range 6<x<10 were not stable under the conditions of preparation. It is concluded that apatites in the range 4<x<6 represent a minimum in the free energy of solid solutions between CaOHA and PbOHA.