Electrical conductivity of pulverulent iron-cobalt molybdates Co1?xFexMoO4: evidence for hopping conduction |
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Authors: | A Steinbrunn C Vautrein B Domenichini |
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Institution: | (1) Laboratoire de Recherche sur la Réactivité des solides, CNRS URA 23, Faculté des Sciences Mirande, B.P. 138, 21004 DIJON CEDEX, France |
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Abstract: | Different mixed iron-cobalt molybdates Co1−xFexMoO4 (0 < x ≤ 1) were prepared by means of a ceramic process. The influence of the isostructural substitution of Co2+ by Fe2+ and Fe3+ on the electrical conductivity of CoMoO4 was studied in the temperature range (50–600°C). The results show that the iron substitution increases the electrical conductivity
and changes the conduction mechanism of CoMoO4. From a band conduction mechanism with an activation energy higher than 0.8 eV the conduction mode transforms into a hopping
mechanism between the Fe2+ and Fe3+ ions in the octahedrally coordinated divalent cation sublattice. The activation energy is lower (0.4 eV) and does not alter
around the polymorphic transition temperature. Owing to careful oxidations of the samples into cation deficient phases it
was shown that the conductivity is proportional to the Fe2+]/Fe3+] ratio. These mild oxidations confirm the hopping mechanism. The presence of Co2+/Co3+ pairs has a minor contribution to the overall conductivity process.
Paper presented at the 2nd Euroconference, Funchal, Madeira, Portugal, 10 – 16 Sept. 1995 |
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