Thermoelectric properties of Ni-based oxides
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Thermoelectric properties of Ni-based oxides R. Funahashi1, 2, M. Mikami2, S. Urata1, T. Kouuchi3, K. Mizuno3 and K. Chong3 1 National Institute of Advanced Industrial Science and Technology Ikeda, Osaka 563-8577, Japan 2 CREST, Japan Science and Technology Corporation Ikeda, Osaka 563-8577, Japan 3 Osaka Electro-Communication University Neyagawa, Osaka 572-0833, Japan e-mail: [email protected] A high-throughput screening technique has been developed and was utilized in the discovery of a new n-type oxide possessing good thermoelectric properties. Screening of metal binary 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 favorably quite low, however, the Seebeck coefficient (S) is as small as –25 µV/K. To enhance the thermoelectric properties of LaNiO3, high-throughput screening was employed to examine candidates from the metal ternary La1–xMxNiO3 and LaNi1–xNxO3 systems. Bi substitution in the La1–xMxNiO3 systems and Cu substitution in the LaNi1–xNxO3 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 105 mV at 1123 K on the high temperature side (TH) with a temperature difference (∆T) of 500 K in air. Resistance of the unicouple (RI) is 18 mΩ at 1123 K in air and increases with increasing 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 = Vo2/4RI, is 152 mW at 1118 K (∆T = 500 K) and increases with temperature. This value corresponds to a volume power density of 1.1 W/cm3. 1. INTRODUCTION Humanity urgently requires solutions to energy and environmental problems that are now approaching critical levels. As one such solution anticipated for development in the near future, electricity could be generated from the vast amounts of waste heat emitted by automobiles, factories, and similar sources to provide a resource-conserving form of energy. Waste heat offers a high-quality energy source equal to about 70% of total primary energy, but is difficult to reclaim due to its source amounts being small and widely dispersed. Thermoelectric generation systems offer the only viable method of overcoming these problems by converting heat energy directly into electrical energy irrespective of source size and without the use of moving parts or production of environmentally deleterious wastes. The requirements placed on materials needed for this task, however, are not easily satisfied. Not only must they possess high conversion efficiency, but must also be composed of non-toxic and abundantly available elements having high chemical stability in air even at temperatures of 800–1000 K. Though CoO2-based oxides with layered structures have been reported to show good p-type thermoelectric properties at high temp
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