Cobalt oxides as potential thermoelectric elements: the influence of the dimensionality
S. Hébert, D. Flahaut, D. Pelloquin, C. Martin, A. Maignan
Laboratoire CRISMAT, UMR 6508 associée au CNRS, ISMRA et Université de Caen, 6 Boulevard du Maréchal Juin, 14050 Caen Cedex, France
The discovery of a large thermopower coexisting with good metallicity in NaCo2O4 has shown the potential applications of oxides as thermoelectric elements. The layered ‘misfit’ cobaltites possess similar CoO2 layers and were found to be promising thermoelectric materials. Their structure can be described as the stacking of CoO2 layers with ‘NaCl’-like layers, with the same a and c parameters but two different b parameters. Because of the trigonal symmetry in the CoO2 planes, the eg band is splitted into two subbands with light and heavy carriers and the transport and magnetic properties of these oxides can be described using a two-band model. Recent results obtained with new misfit phases will be discussed in this framework.
Another family of cobalt oxides has been investigated. In Ca3Co2O6, ferromagnetic chains distributed on a triangular lattice are antiferromagnetically coupled. The thermopower is very large, close to + 700mV/K at 300K but the resistivity is too large, close to 10 W.cm. Attempts to reduce the resistivity while keeping a large S will be presented.
Finally results showing that in 3D cobaltites derived from LaCoO3, n type thermoelectric materials can be obtained will be presented. Their high temperature performance will be compared to the ones of n type manganites.