Abstract
A comparison study has been made between the cubic monoxides and oxide spinels of iron, manganese, and cobalt in terms of cation defect structures and electrical properties. Although all six oxides share close-packed oxygen sublattices and have similar point defect structures, there are considerable differences between conduction processes. Whether or not an octahedral/tetrahedral cation exchange reaction occurs may play a central role in governing conduction. In the iron oxides, n-type small polaron conduction takes place with small hopping energies (0.11-0.16 eV) between octahedral Fe2+ and Fe3+, with the cation intersite reaction playing a dominant role. Very different behaviors are observed in the spinels and monoxides of manganese and cobalt. Intersite exchange is highly unlikely in these materials. Instead, disproportionation on the octahedral sites results in p-type small polaron conduction with larger hopping energies (0.25, 0.79 eV) between octahedral M4+ and M3+ in the spinels of cobalt and manganese. At higher temperatures, yet another small polaron mechanism prevails in cobalt spinel. In contrast, no hopping energy is apparent for either MnO or CoO.
Original language | English (US) |
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Pages (from-to) | 37-43 |
Number of pages | 7 |
Journal | Physica B+C |
Volume | 150 |
Issue number | 1-2 |
DOIs | |
State | Published - May 1988 |
Funding
The author gratefully acknowledges the support of the National Science Foundation (Grant Nos. DMR-8605095 and DMR(MRL)-8520280) for the spinel work and the support of the Department of Energy (Grant No. DE-FG02-84ER45097) for the monoxide work. Much of the work was carried out in central facilities of the Materials Research Center. The help of Tony Witt with measurements and Steve Dorris and Glen Sykora with the manuscript is gratefully acknowledged.
ASJC Scopus subject areas
- General Engineering