We present measurements of electrical resistivity, thermal conductivity and thermopower of polycrystalline Sr-doped LaCoO3 with composition La0.95Sr0.05CoO3. Our data show that the investigated compound exhibits a very respectable room temperature thermoelectric figure of merit value of 0.18. Our results not only show that oxides are promising candidates for thermoelectric cooling applications, but also point towards the need for careful theoretical calculations that will serve as a guide in producing the next generation of thermoelectric materials.Comment: 13 pages, 3 figures, Accepted in Appl. Phys. Lett. scheduled to appear on Feb 17, 2004 issu

Several polycrystalline samples of the half-Heusler alloy NiMnSb were grown by arc melting of stoichiometric and nonstoichiometric amounts of high-purity constituent elements. The structure and the phase-purity of the prepared samples were examined systematically by powder x-ray diffraction. The transport properties of the best sample, with saturation magnetization M s (5 K) ϭ4 B /formula unit, were studied by measuring electrical resistivity, thermal conductivity, and thermopower. Features in both magnetic and transport data are consistent with NiMnSb being in a half-metallic state at low temperatures, i.e., the conduction electrons are fully spin polarized. However, point-contact Andreev reflection measurements on the same sample at 4.2 K demonstrate only ϳ45% spin polarization.

We present the results of a systematic investigation of the thermal conductivity, Seebeck coefficient and electrical resistivity for selected members (x=0.3, 0.7, 0.8, and 1) of the LaNi1−xCoxO3 solid solution in the temperature range of 80⩽T⩽320 K. Substitution of Ni by Co drives the system from n-type metallic phase with low thermopower values into p-type semiconducting phase with high thermopower values of the order of hundreds of μV/K. But the thermal conductivity observed varies only slightly with the composition, x, over the temperature range investigated. The latter effect also holds true for the lightly hole doped x=0.8 member (in substituting Sr for La). Our results suggest that semiconducting members of the LaNi1−xCoxO3 solid solution can be classified as “phonon glass and electron crystal” systems. The highest room temperature figure of merit was exhibited by the x=0.8 member (ZT=0.022), which is comparable to that of single crystal NaCo2O4 (ZT=0.03).

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