A new approach for the determination of multiple cation locations and ordering, using the example of natural and heat-treated columbites

A new approach is proposed to determine unambiguously the location of four cations within the crystal structure of a natural AB(2)O(6) columbite-type compound and derivatives, when submitted to order-disorder transitions caused by heat treatments. This method is based on the successive use of electron microprobe analysis to determine the cation concentration, Mossbauer spectroscopy to identify the Fe occupation, and a crystal structure determination of the samples combining Rietveld refinements of both neutron and X-ray diffraction. This approach is tested successfully to investigate (Fe, Mn, Nb, Ta) natural minerals as well as oxides obtained by heat treatment of the initial AB(2)O(6) columbite-type compound.