New bismuth calcium oxysilicate with apatite structure: Synthesis and structural characterization

New bismuth calcium silicon oxide Ca4Bi4.3(SiO4)(HSiO4)5O0.95, with apatite structure has been synthesized. The structure was refined from powder X-ray diffraction data. The refinement revealed that the phase has P63/m (176) space group with unit cell parameters a=b=9.6090(7) Å, c=7.0521(7) Å, V=563.9 Å3 and c/a=0.734. The Rwp factor at Rietveld refinement was equal to 0.082. The synthesized phase has an unusual quantity of cation vacancies in a crystal lattice. Mechanisms of compensation of the excess charge of a lattice are considered and checked experimentally using the FT-IR spectroscopy, the thermal analysis and the XPS analysis.