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Günther, A.; Hochleitner, R.; Lohringer, H.; Schmidbauer, E.; Schöttler-Himmel, A.; Volk, M. (2017): Effect of oxygen partial pressure during preparation of rutile-type FeNbTiO6 on electrical and dielectric properties, thermopower and Mossbauer spectra. In: Journal of Physics and Chemistry of Solids, Vol. 104: pp. 91-102
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Abstract

Electrical and dielectric properties were measured on ruffle-type FeNbTiO6, sintered in air, CO2 or 5%H-2/CO2 atmosphere between temperatures of 1423 and 1573 K. The individual samples show characteristic differences in DC and AC conductivity, dielectric constant epsilon(w) (w is angular frequency), dielectric loss and dissipation factor. Attempts were made to distinguish between bulk, grain boundary (GB) and sample-electrode (SE) processes. Samples show very high relaxor-like epsilon(w) peaks at 500-600 K using Ag-paint contacts as expected from previous studies during preparation in air that is of interest for industrial application;utilizing Pt-paint and using slightly reducing sintering conditions, a clear variation was observed. These findings point to a notable influence of GB and/or SE effects on the experimental epsilon(w), in addition to the intrinsic origin by polar nanoregions, as suggested earlier. Complex plane impedance plots are characterized by semicircular arcs due to bulk, GB and/or SE charge transport. The derived DC conductivity am shows Arrhenius behavior with activation energy of E-A approximate to 0.27-0.37 eV and sigma(DC)(300 K) approximate to 1x10(-6)-3x10(-4) Omega(-1)cm(-1) for the bulk, E-A approximate to 0.7-0.9 eV and sigma(DC)(300K)approximate to 5x10(-10)-1x10(-4) Omega(-1)cm(-1) for GB and/or SE processes, depending on the preparation conditions. The thermopower is small and negative, hence n -type conduction occurs and the charge carriers are electrons or electron polarons. Fe-57 Mossbauer spectroscopy enabled to gain knowledge of local nonstoichiometry in the environment of Fe cations, presumably affecting electrical conduction in the bulk and GBs;after sample preparation in reducing conditions, apart from Fe3+ also the presence of Fe2+ ions was established.