Promising p-type thermoelectric properties of a layered transition metal oxide NaxCoO2 are discussed in terms of crystal chemistry and the conduction mechanism. Highly anisotropic spatial distribution of 3d orbitals coupled with an unusually short Co-Co interatomic distance in the ab plane, along which edge-sharing CoO6 octahedra connecting each other to form the CoO2 sheets, strongly suggest that Co3d dε-dε (t2g-t2g) direct overlapping is plausible for establishing hole conduction in the valence band with a fairly covalent character. An extremely low thermal conductivity (≤1 W/mK) of the oxide is also revealed, implying contribution of the randomly distributed Na vacancies and an inherent advantage of materials with low-dimensional crystal structure. In spite of insufficient densification, sintered bodies fired under atmospheric pressure shows ZT≈0.5. Possible influence of the ionic conduction of Na+ on the thermoelectric properties of the oxide is also examined.
|Number of pages||4|
|Journal||International Conference on Thermoelectrics, ICT, Proceedings|
|Publication status||Published - Dec 1 1999|
|Event||18th International Conference on Thermoelectrics (ICT'99) - Baltimore, MD, USA|
Duration: Aug 29 1999 → Sep 2 1999
All Science Journal Classification (ASJC) codes