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Takao Mori1

1, National Institute for Materials Science (NIMS), Tsukuba, , Japan

Efforts worldwide to find viable thermoelectric (TE) materials are intensifying and property enhancement mechanisms are being actively researched [1]. We have discovered that magnetic semiconductors can have enhanced thermoelectric properties, which are indicated to originate from magnetic and carrier-magnon interactions [2-4]. A clear example is given where magnetic Mn-doping into nonmagnetic CuGaTe2 resulted in a monotonic increase of effective mass, accompanied by appearance of a sizable indicated on-site exchange interaction between the Mn spins and conduction electrons, and significant enhancement of the power factor [5]. I will also present recent results on chalcogenide spinel compounds which had previously been considered to be of poor thermoelectric performance. Unconventional Sb doping into CuCr2S4 led to an initial promising ZT value of 0.43 [6]. CuCr1.7Sb0.3S4 is a magnetic semiconductor with ferromagnetic ground state and with an estimated high effective mass of 5.9 m0 (m0 =free electron mass). Exciting results have also been obtained for different CuX2Te4 (X=magnetic transition metal) compounds and variants, and will be presented. Modules were also constructed from original magnetic sulfides and the performance evaluated. This work is supported by CREST, JST and project members are acknowledged.
References
1) T. Mori, “Novel principles and nanostructuring methods for enhanced thermoelectrics”, Small, in press doi: 10.1002/smll.201702013 (2017).
2) N. Tsujii and T. Mori, Appl. Phys. Express, 6, 043001 (2013).
3) R. Ang, A. U. Khan, N. Tsujii, K. Takai, R. Nakamura, and T. Mori, Angew. Chem. Int. Ed., 54, 12909 (2015).
4) H. Takaki, K. Kobayashi, M. Shimono, N. Kobayashi, K. Hirose, N. Tsujii, and T. Mori, Appl. Phys. Lett. 110, 072107 (2017).
5) F. Ahmed, N. Tsujii and T. Mori, J. Mater. Chem. A, 5, 7545 (2017).
6) A. U. Khan, R. A. R. A. Orabi, A. Pakdel, J. B. Vaney, B. Fontaine, R. Gautier, J. F. Halet, S. Mitani, and T. Mori, Chem. Mater., 29, 2988 (2017).

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