Electrical Resistivity, Thermopower, and57Fe Mössbauer Study of FeNbO4

✍ Scribed by E. Schmidbauer; J. Schneider

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 420 KB
• Volume: 134
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7551

✦ Synopsis

The electrical charge transport was investigated on sintered semiconducting FeNbO 4 and compositions with a slight surplus of Nb in the monoclinic (pseudorhombic) wolframite and orthorhombic -PbO 2 structures using electrical DC, AC resistivity (complex plane impedance analysis), and thermopower in the temperature T range+100-900 K. At low T, the experimental crystallite conductivity is consistent with a variable-range hopping charge transport model, characterized by the relationship ln JT ؊1/4 . In the high-T region, activation energies E A for the extrapolated crystallite DC resistivity are found up to E A +0.7 eV. The thermopower is negative, with " " increasing with rising T in the low-T region, and between +120 and 300 K the data can be approximately described by a linear -T 1/2 relation for both structures that is theoretically predicted for variable-range hopping. Above 300 K, the curves bend and becomes constant with values :؊270 and ؊220 to ؊230 V/K. Suggesting electron hopping Fe 2؉ PFe 3؊ to be the dominating charge transport mechanism, the high-T data are in part compatible with the assumption that all or a dominant fraction of Fe 2؉ and Fe 3؉ are taking part in this process; this result follows from the derived concentration ratio [Fe 2؉ ]/ [Fe 3؉ ], which is similar to that determined from 57 Fe Mo] ssbauer spectra at 79 K.