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

Abstract

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, Mö ssbauer 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.

Effect of Lubricants and Annealing Treatment on the Electrical Conductivity and Microstructure of Rolled Copper Foil

“…Figure 3a shows the modulated crystal structure; several different orientations are clearly apparent. Modulated structures are caused by ordering of the cations occupying different crystal sites 19 and by slight shifts in the position of atoms in space (vide infra). Slippage is among the copper crystals is apparent in Fig.…”

Magnetic behavior of the NixFe1−xNb2OSarvezuk1, Gusmao2, Cunha3 et al. 2012Phys. Rev. BSelf Cite173131View full textAdd to dashboardCite

“…The site assignment is justified because the quadrupole splitting is inversely correlated with the octahedral distortions. 29 Indeed, it has been shown 24,30 that the FeO 6 octahedra are less distorted than the NbO 6 ones. We consequently attribute the single doublet observed here ( E Q ∼ 1.8 mm/s) to Fe 2+ in the more distorted FeO 6 octahedra.…”

“…In natural (and, consequently, partially ordered) columbite samples, [27][28][29] the Mössbauer spectra present two quadrupole doublets ( E Q ), both attributed to Fe 2+ in different octahedrally coordinated sites. The site assignment is justified because the quadrupole splitting is inversely correlated with the octahedral distortions.…”

Wodginite as an indicator mineral of tantalum-bearing pegmatites and granites

“…Thus, the crystal lattice of wodginite is a derivative of a disordered lattice of ixiolite and more ordered than the columbite-tantalite lattice AB2O6, consisting of layers of octahedra ABB. Wodginite can be considered as a maximally ordered ixiolite with an enlarged fourfold elementary cell [60][61][62]. This is confirmed experimentally: ixiolite containing SnO2 (up to 19.5 %) and TiO2 (up to 15.8 %) when heated turns into wodginite.…”

“…The Fe 3+ /Fe 2+ ratio in wodginite has a higher value than in tantalite [41]. Sn 4+ and Fe 3+ cations are interchangeable in the structure of wodginite and in the absence of tin, its role is played by Fe 3+ [8,61,62]. In iron-bearing varieties of WGMferrowodginite, ferrotitanowodginite, "wolframowodginite"electron neutrality is achieved by occupying position B of a part of tantalum cations: 2 [15,59].…”