title: Lattice parameters and cation distribution of solid solutions of calcium and lead hydroxyapatite.
abstract: 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 degrees C in a steam of CO2-free water vapor of 1 atm. The samples were apatitic in the range 0 less than x less than 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 six-fold position for cations. There was a miscibility gap in the apatite series of solid solutions in the range 1 less than x less than 4, whereas apatites in the range 6 less than x less than 10 were not stable under the conditions of preparation. It is concluded that apatites in the range 4 less than x less than 6 represent a minimum in the free energy of solid solutions between CaOHA and PbOHA.
mesh_terms: D002118:Calcium; D002412:Cations; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003461:Crystallography; D017886:Durapatite; D006801:Humans; D006882:Hydroxyapatites / Q000032:analysis; D007854:Lead; D008956:Models, Chemical; D014961:X-Ray Diffraction
chemical_list: D002412:Cations; D006882:Hydroxyapatites; D007854:Lead; D017886:Durapatite; D002118:Calcium