MN(V) POLYHEDRON SIZE IN BA-10((P,MN)O-4)(6)F-2 - VIBRATIONAL SPECTROSCOPY AND EXAFS STUDY

This paper reports the study of manganese substituted barium fluoroapa tite Ba-10(P1-xMnxO4)(6)F-2 with 0 less than or equal to x less than o r equal to 0.20. X-rays diffraction investigation indicates that the p hosphate-manganate solid solution is complete, at least for this compo sition range, and follows Vegard's law, while diffuse reflectance and fluorescence spectra confirm that Mn(V) substitutes for P(V) in the ba rium apatite lattice. EXAFS experiment, at the manganese K edge, perfo rmed on the x = 0.2 compound, indicates that the Mn(V)-O distance is 1 .73 Angstrom, a much larger value than the P-O distance equal to 1.54 Angstrom. The (MnO4)(3-) vibrational mode frequencies, deduced from th e IR and Raman spectra are almost independent of the x value. This ind icates that, even at very low manganese content (x = 0.001), the Mn-O distance is also very close to 1.73 Angstrom. The Mn(V) ion distorts t he barium apatite lattice to a large extent when it substitutes for P( V) and imposes its own size to the host sites.