Different versions of a thermoelectric unicouple composed of p-type Ca2.7Bi0.3Co4O9 (Co-349) and n-type La0.9Bi0.1NiO3 (Ni-113) bulks were constructed using Ag paste containing p- and n-type oxide powders, prepared from the same bulks, for connection of the p and n legs, respectively. Internal resistance (RI) of the unicouple corrected using Ag paste containing 6 wt. % of the oxide powders is 26.2mΩ at 1073K in air and decreases with increasing temperature. Maximum output power (Pmax), evaluated using the formula Pmax=VO2∕4RI, (VO is open-circuit voltage), is 94mW at 1073K (ΔT=500K) and increases with temperature. This value corresponds to a volume power density of 0.66W∕cm3.

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A high-throughput screening technique has been developed and utilized in the discovery of a new n-type oxide possessing good thermoelectric properties. With this technique, 1000 samples can be prepared via a sol–gel method and their Seebeck coefficient (S) evaluated all within a day. For evaluation of S, a ‘Seebeck tester’ consisting of two pairs of thermocouples, a heater and a voltage meter, was developed. S values measured using the Seebeck tester more or less coincide with those using a conventional method. The validity of this technique was proven by Ca–Co–O and Na–Co–O systems. Screening ternary systems consisting of 3d transition metals using this technique showed LaNiO3 to possess the desired n-type properties. Electrical resistivity (ρ) of this oxide is favourably quite low; however, S is as low as –25 µV K−1 at high temperature. To enhance the thermoelectric properties of LaNiO3, high-throughput screening was employed to examine candidates from the metal ternary systems La1–xM1xNiO3 and LaNi1–xM2xO3. Bi substitution in the La1–xM1xNiO3 systems and Cu substitution in the LaNi1–xM2xO3 systems were found to be effective for improvement of S and ρ, respectively. A thermoelectric unicouple composed of p-type Ca3Co4O9 (Co-349) and n-type LaNiO3 (Ni-113) bulks was constructed. Open-circuit voltage (Vo) of the unicouple reaches 100 mV at 1073 K on the hot side (TH) with a temperature difference (ΔT) of 500 K in air. Resistance of the unicouple (RI) is 26 mΩ at 1073 K in air and increases with increase in temperature. The Vo values are consistent with those calculated using S values for each oxide leg. Maximum power (Pmax), which was evaluated using the formula Pmax = V2o/4RI, is 94 mW at 1073 K (ΔT = 500 K) and increases with temperature. This value corresponds to a volume power density of 660 mW cm−3.

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