Layered CobaltatesMOI Home | CMPMSD Home | Contacts IntroductionThermoelectric (TE) elements can generate heat from a voltage gradient
(Peltier refrigerators) or a voltage from a temperature gradient (thermogenerators). The search for new thermoelectric materials has become an important issue since there exists numerous sources of waste-heat which could be converted to electrical energy by using non polluting thermoelectric devices. The efficiency of such a device is characterized by the figure of merit defined as
Z=S2/ρκ, where S is thermoelectric power, ρ the resistivity and κ the thermo-conductivity. Materials used in TE devices usually have ZT in the order of 1, where T is the absolute temperature. The highest thermoelectric performance materials are intermetallic compounds such as
Bi2Te3/Sb2Te3 alloys. The drawbacks of the conventional TE materials are that they have low melting, decomposition, and oxidation-temperatures, and they have content of harmful or rare elements, and notably deficient in the temperature range of waste heat (600-1000K).
Our ResearchThe origin of the coexistence of metallicity with a large thermoelectric power is still unclear. Two models have been proposed. The first one takes into account the spin degeneracy associated to the different cobalt valency and spin states [W. Koshibae et al., Phys. Rev. B 62, 6869 (2000)]. In the second one [D. J Singh, Phys. Rev. B 61, 13397 (2000)], a two-band model has been proposed: a band of light carriers responsible for metallicity coexists with a narrow band of heavy carriers in which the Fermi energy level lies. A peak in the Density of States near
EF would be responsible for the large thermoelectric power. Last Modified: January 31, 2008 |