Crystal structure of cobalt-substituted calcium hydroxyapatite nanopowders prepared by hydrothermal processing

A series of cobalt-exchanged hydroxyapatite (CoHAp) powders with different Ca/Co ratios and nominal unit-cell contents Ca_10−xCo_x(PO₄)₆(OH)₂, x = 0, 0.5, 1.0, 1.5 and 2.0, were synthesized by hydrothermal treatment of a precipitate at 473 K for 8 h. The effects of cobalt content on the CoHAp powders were investigated using inductively coupled plasma emission spectroscopy, particle size analysis, transmission electron microscopy and high-resolution transmission electron microscopy analyses, as well as X-ray powder diffraction including Rietveld analysis.