Carbonate apatite type A synthesized at high pressure: new space group (P(3)over-bar) and orientation of channel carbonate ion

摘要

A new space group and structure are reported for type A carbonate apatite (CAp) of composition Ca-10(PO4)(6)[(CO3)(x)(OH)(2-2x)] x greater than or equal to 0.5, synthesized at 2 GPa, 1400-1500degreesC. Crystal data are trigonal, space group P (3) over bar, Z = 1; x approximate to 0.75, a = 9.5211(3), c = 6.8725(2)Angstrom , V = 539.5 Angstrom(3), R = 0.030, and D-x = 3.152g/cm(3); x approximate to 0.50, a = 9.4917(2), c = 6.8758(3) Angstrom, V = 536.5 Angstrom(3), R = 0.030, and D-x = 3.150g/cm(3). In the P (3) over bar structure, the type A carbonate ion is ordered along the apatite channel at z = 0.5. Two of the oxygen atoms of the carbonate ion lie close to the c-axis, with the plane of the ion canted similar to 12degrees. FTIR spectra are similar to that of type A carbonate hydroxylapatite. The present structure may be an appropriate model for the orientation of the type A carbonate ion in bone and enamel. (C) 2003 Elsevier Inc. All rights reserved. [References: 34]