A synchrotron study of Na(2.27)Ho(7.73)(SiO(4))(6)O(0.72).

ABSTRACT

A well crystallized powder sample of sodium holmium orthosilicate oxyapatite, Na(2.27)Ho(7.73)(SiO(4))(6)O(0.72), was obtained after mechanical milling and thermal treatment at 1123 K. Crystal structure analysis was performed from the results of Rietveld refinement of the synchrotron diffraction data. As in other rare-earth orthosilicate apatites, sodium cations appear located sharing with holmium the 4f Wyckoff position at the center of a tricapped trigonal prism. In its turn, holmium almost fully occupies the 6h position at the center of a seven-coordinated penta-gonal bipyramid. A small quantity of Na atoms was found at this site. No vacancies are present in the two independent crystallographic sites available for Ho and Na atoms.