Preparation and structure refinement of monoclinic hydroxyapatite

Monoclinic hydroxyapatite was synthesized by a wet method followed by heati ng in air at 1473 K for 1 h, The product is carbonate-free and has a Ca/P r atio of 1.65, which is slightly lower than the theoretical value (1.67) of hydroxyapatite. The crystal structure mas investigated by Rietveld refineme nt using X-ray powder diffraction data. The structure has monoclinic symmet ry with the space group P2(1)/b (No, 14), Z = 4, Dx = 3.14 g cm(-3), and th e lattice constants are a = 9.426(3) Angstrom, b = 18.856(5) Angstrom, c = 6,887(1) Angstrom, and gamma = 119.97(1)degrees. The hydroxyl ions have an ordered arrangement along the hydroxyl columns. The hydroxyapatite prepared in the present study is 98% monoclinic. (C) 1999 Academic Press.