Thermoelectric Properties of Polycrystalline Ca0.9Yb0.1MnO3 Prepared from Nanopowder Obtained by Gas-Phase Reaction and Its Application to Thermoelectric Power Devices

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Ca0.9Yb0.1MnO3 nanopowder prepared by a gas-phase reaction (GPR) consisted of well-dispersed particles with an average diameter of 47 nm. Sintering of this GPR powder proceeded rapidly and at a lower temperature than that required for a comparable powder prepared by conventional solid-state reaction (SSR). The sintered bulk material from the GPR powder (GPR-bulk) consisted of small grains with an average diameter of 620 nm; this morphology is completely different to that of the SSR-bulk in which larger grains bind together to form a network-like structure. A maximum power factor of 0.19 mW$\cdot$m-1$\cdot$K-2 was obtained for GPR-bulk at 973 K; this value is higher than that of SSR-bulk, mainly as a result of the lower electrical resistivity of GPR-bulk. The thermal conductivity of GPR-bulk is also lower than that of SSR-bulk, possibly because of increased phonon scattering at the grain boundary. The maximum value of the dimensionless figure of merit of 0.13 was obtained for GPR-bulk at 1073 K; this value is about 1.5-fold higher than that for SSR-bulk at 773 K. A unicouple device consisting of a p-type Ca2.7Bi0.3Co4O9 leg and an n-type Ca0.9Yb0.1MnO3 (GPR-bulk) leg was fabricated. Both oxide legs used for the measurement are 3.1–3.5 mm in both width and thickness and ${\sim}5$ mm in height. The device generated up to 0.14 W of power when the hot- and cold-side temperatures at the ends of the oxide legs were 1095 and 390 K, respectively.
2010-07-25