Coexistence of rutile and trirutile phases in a natural tapiolite sample

摘要

We report X-ray powder diffraction (XRD), electron probe microanalysis (EPMA), and Mossbauer spectroscopy (MS) measurements performed on a natural tapiolite with composition Fe0.57Mn0.37Ti0.10Ta1.27Nb0.67O6. XRD and MS suggest that besides being partially ordered the as-collected sample is a mix- ture of trirutile (P4(2)/mnm, a = 4.7532 (9) Angstrom, c = 9.228 (7) Angstrom) and Nb-rich rutile (P4(2)/mnm, a = 4.856(2) Angstrom, c = 3.098(1) Angstrom) structures. The Mossbauer spectra of the rutile (Fe, Mn, Ta, Nb)O-2 were fitted to Delta = 1.72+/-0.05 mm/s and delta = 1.10+/-0.03 mm/s at 300 K and to Delta =2.10+/-0.06 mm/s and delta = 1.18+/-0.03 mm/s at 80 K. The present results suggest that cation ordering in compounds of the tapiolite series can be easily assessed by Mossbauer spectroscopy in a way similar to that as previously demonstrated for the columbite series. (C) 2002 Elsevier Science. [References: 22]