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Electrical resistivity, thermopower, and Fe-57 Mossbauer study of FeNbO4

Schmidbauer, E., and J. Schneider (1997), Electrical resistivity, thermopower, and Fe-57 Mossbauer study of FeNbO4, Journal of Solid State Chemistry, 134(2), 253-264.

The electrical charge transport was investigated an sintered semiconducting FeNbO4 and compositions with a slight surplus of Nb in the monoclinic (pseudorhombic) wolframite and orthorhombic alpha-PbO2 structures using electrical DC, AC resistivity (complex plane impedance analysis), and thermopower Theta in the temperature T range approximate to 100-900 It. At low T, the experimental crystallite conductivity sigma is consistent with a variable-range hopping charge transport model, characterized by the relationship ln sigma proportional to T-1/4. In the high-T region, activation energies E-A for the extrapolated crystallite DC resistivity are found up to E-A approximate to 0.7 eV. The thermopower Theta is negative, with \Theta\ increasing with rising T in the low-T region, and between approximate to 120 and 300 K the data can be approximately described by a linear Theta-T-1/2 relation for both structures that is theoretically predicted for variable-range hopping. Above 300 K, the curves bend and Theta becomes constant with values Theta similar to -270 and -220 to -230 mu V/g. Suggesting electron hopping Fe2+ --> Fe3- to be the dominating charge transport mechanism, the Theta high-T data are in part compatible with the assumption that all or a dominant fraction of Fe2+ and Fe3+ are taking part in this process; this result follows from the derived concentration ratio [Fe2+]/[Fe3+], which is similar to that determined from Fe-57 Mossbauer spectra at 79 K. (C) 1997 Academic Press.
  author = {E. Schmidbauer and J. Schneider},
  journal = {Journal of Solid State Chemistry},
  number = {2},
  pages = {253-264},
  title = {{Electrical resistivity, thermopower, and Fe-57 Mossbauer study of FeNbO4}},
  volume = {134},
  year = {1997},
  language = {en},
%0 Journal Article
%A Schmidbauer, E.
%A Schneider, J.
%D 1997
%N 2
%V 134
%J Journal of Solid State Chemistry
%P 253-264
%T Electrical resistivity, thermopower, and Fe-57 Mossbauer study of FeNbO4
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