Morphology control of materials as a way to dramatically improve the physical properties
Dr. Takao Mori
Hiroshima University and
National Institute for Materials Science
Abstract: The useful energy conversion of waste heat is a huge incentive to find viable thermoelectric materials. One need exists to develop materials which can function at high temperature. Boron-rich cluster compounds are attractive materials for their stability under high temperature, typically exhibiting melting points above 2200 K. As a synthesis method it has been found that addition of small amounts of third elements like carbon, nitrogen, and silicon can result in the formation of novel and varied rare-earth boron cluster structures . REB44Si2 compounds exhibit Seebeck coefficients greater than 200 mV/K at high temperatures and unlike most compounds, the figure of merit shows a steep increase at T>1000 K [2,3]. Homologous RE-B-C(N) compounds were recently discovered to be the long awaited n-type counterparts to p-type boron carbide .
In this talk, I would like to give some perspectives on new development in high temperature thermoelectric materials, such as synthesis and discovery of some novel borides, silicides, and oxides. I will also especially focus on ways to control the morphology of materials, which should have wide applicability for various materials. Morphology control has been found to be a powerful method to improve the physical properties. SPS (Spark Plasma Sintering) is an increasingly appreciated tool for rapid synthesis and enabling control of the morphology of materials. Strategies will also be described for selection of sintering additives which have beneficial double effect, i.e. effect on the sintering/densification properties and also simultaneous effect as electronic dopants.
- T. Mori, in Handbook on the Physics and Chemistry of Rare Earths, Vol. 38, ed. K. A. Gschneidner Jr., J.-C. Bunzli, and V. Pecharsky (North-Holland, Amsterdam, 2008) p. 105-173.
- T. Mori, J. Appl. Phys. 97, 093703 (2005), 179, 2908 (2006).
- T. Mori, D. Berthebaud, T. Nishimura, A. Nomura, T. Shishido, and K. Nakajima, Dalton Transactions, 39, 1027 (2010). Hot Article.
- T. Mori et al., J. Solid State Chem., 179, 2908 (2006).
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