Location of type B carbonate ion in type A-B carbonate apatite synthesized at high pressure

The structure of a complex, disordered type A-B carbonate apatite (CAp) of approximate composition Ca-10(PO4)(6-y)(CO3)(x+(3/2)y)(OH)(2-2x), x-0.7, y-0.6, synthesized at 3GPa, 1400degreesC has been determined using single-crystal X-ray diffraction and FTIR spectroscopy at room temperature and pressure. Crystal data are: hexagonal, space group P6(3)/M, Z = 1; a = 9.5143(3), c = 6.8821(2) Angstrom, V = 539.5 Angstrom(3), and R = 0.025. There are three structural locations for the carbonate ion. The channel carbonate is mainly in the closed vertical configuration of the M structure, with two of its oxygen atoms close to the c-axis (A1 carbonate; IR bands at 1541 and 1449cm(-1)), but subordinate amounts are also located in an open vertical configuration (A2 carbonate; IR bands at 1563 and 1506cm(-1)). The type B carbonate ion is located close to the sloping faces of the PO4 tetrahedron (IR bands at 1474 and 1406cm(-1)), confirming earlier inferences from polarized IR spectra. (C) 2004 Elsevier Inc. All rights reserved.