CRYSTAL-STRUCTURE OF SR-SUBSTITUTED HYDROXYAPATITE SYNTHESIZED BY HYDROTHERMAL METHOD

Single crystals of Sr-substituted hydroxyapatite, (Ca9.42Sr0.18 H0.8(PO4)6(OH)2, up to 0.2 x 0.2 x 5 mm3 maximum size were grown hydrothermally from calcium hydrogenphosphate (CaHPO4) and strontium hydrogenphosphate (SrHPO4) in a long tube-type autoclave using a temperature gradient technique. The single crystals, containing 1.92 mole% Sr to (Ca + Sr) and having a (Ca + Sr)/P atomic ratio of 1.60, had a hexagonal-prismatic shape with density of 3.207 g/cm3. The crystal had a hexagonal system, space group P6(3)/m with a = 9.3920(7) angstrom, c = 6.890(1) angstrom, and Z = 1. A hexagonal-prismatic crystal, 165 x 165 x 231 mum3 in size, was used for crystal structure refinement. The atomic parameters in P6(3)/m were refined to R = 5.9% and R(W)angstrom = 6.3% with 2018 independent reflections. The preferential substitution site of Sr for Ca was determined as the Ca(1) site. (C) 1994 Academic Press, Inc.