Local structural properties of (Mn,Fe)Nb₂O₆ from Mössbauer and X-ray absorption spectroscopy

Abstract

The MnNb 2 O 6 -FeNb 2 O 6 solid solution has been investigated by Fe-K-and Mn-K-edge X-ray absorption (XANES and EXAFS), and Mö ssbauer spectroscopy. The first-shell M-O bond lengths deduced from EXAFS show a fairly small compositional dependence. A degree of static disorder, which increases with increasing manganese content, is clearly seen by the loss of correlation for the next-neighbour (NN) interaction. Hyperfine parameters from Mö ssbauer spectra are consistent with variations in the average environment, as recorded by X-ray data. Line broadening of the Mö ssbauer spectra provides evidence for next-neighbour effects and is consistent with there being no significant clustering of Fe or Mn within the samples. There appear to be differences in the way the columbite structure accommodates Fe 2+ and Mn 2+ions. In ferrocolumbite all the Fe octahedra are close to being identical, while there are local structural heterogeneities at a longer length scale, presumably in ordering the precise topology of polyhedra immediately adjacent to the octahedron. By contrast, the manganocolumbite seems to have some diversity in the precise coordination at the MnO 6 octahedra, but a greater uniformity in how the adjacent polyhedra are configured around them.

Effect of Cobalt Substitution on Li3–2xCoxN Local Structure: A XAS Investigation

“…This disorder effect on the diffraction patterns is fully described in Guinier’s textbook . It has been confirmed by the complementary diffraction and EXAFS studies of various materials such as metallic alloys, , metallic oxides, − and lamellar compounds. , As in our case, all these materials are solid solutions. Their XRD refinements lead to linear variations of crystal lattices versus composition.…”

Morphological control of CaxMn1−xNb2O6 columbites for use as lithium hosts in batteries

“…In the case of the series of naturally occurring (Fe x Mn 1− x )(Ta y Nb 2− y )O 6 , site mixing between Mn and Fe O h sites in the TaO 6 and NbO 6 was found when neutron and PXRD refinements were combined. 14 Tarantino et al 20 showed for a series of (Mn,Fe)Nb 2 O 6 that the EXAFS data have small composition dependence in the first shell (metal–oxygen bond lengths from Mn K- and Fe K-edges), which suggests that differences between the local structure of an ordered or disordered MNO would be minor, and it agrees with the observations here made.…”

“…The structure of the mineral columbite (Fe,Mn)(Nb,Ta) 2 O 6 and annealed samples have been investigated through combining laboratory X-ray and neutron diffraction refinements and 57 Fe Mössbauer spectroscopy. 14,19,20 These studies concluded that interlayer mixing between A and B exists. In the extreme case the ixiolite structure is observed.…”

Pressure-Induced Phase Transition in Mn(Ta,Nb)2O6: An Experimental Investigation and First-Principle Study

“…The families of oxide compounds with the general formula AB 2 O 6 (A-Fe, Mn, Mg, Zn, Ca, Co, Ni; B-Ta, Nb, V, Pb) have attracted much interest because of their important use in technological applications. − The high permittivity and low dielectric loss at microwave frequencies make these materials suitable for use as resonators in the fields of satellite communications, supercapacitors in electric cars, ceramics in microwave technology, and many other electric devices. − The AB 2 O 6 compounds are also used as important intermediates for the synthesis of perovskite structure related materials . Among AB 2 O 6 compounds, (Mn,Fe)­(Nb,Ta) 2 O 6 with A and B sites mainly occupied by Mn 2+ or Fe 2+ and Ta 5+ or Nb 5+ , respectively, deserves special attention due to its potential applications …”