Rietveld analysis and Fourier maps of hydroxyapatite

Rietveld analysis was applied to the X-ray powder diffraction data of well-crystallized hydroxyapatites synthesized at 80 °C and pH 7.4. The least-squares refinement program adopted for Rietveld analysis showed good pattern fitting with the calculated profile. The a- and c-axis dimensions, a = 0.943046 ± 0.000126 nm and c = 0.687485 ± 0.000104 nm, were obtained and compared with the data estimated from a single peak. The lattice dimensions obtained by Rietveld analysis were much closer to the values of a single crystal, a = 0.9432 nm and c = 0.6881 nm. Fourier analysis was also performed. The maps of electron densities expressed the existing possibility of each atom composing hydroxyapatite in the crystal structure. In particular, columnar calcium and screw-axis calcium were clearly revealed. These data agreed well with the computer graphics model of hydroxyapatite reported previously.