Abstract
Layered titanium disulfide has been reported to show a high thermoelectric power factor due to its two-dimensional electronic state. However, its high thermal conductivity makes its conversion efficiency too low for practical applications. We attempted to intercalate a layer of BiS, SnS or PbS into the van der Waals gap of the TiS2 layers to form natural superlattices with general formula (MS)1+x(TiS2)n (M=Bi, Sn, Pb; n=1, 2) and the lattice thermal conductivity was significantly reduced by intercalation. Sound velocity measurement indicated that the chemical bond between the hetero-layers was greatly weakened by intercalation leading to the ultra-low lattice thermal conductivity.
HRTEM observations revealed the lattice disorder increased in the order of Pb, Sn, Bi for (MS)1+x(TiS2)2, and the lattice thermal conductivity decreased significantly with increasing disorder. In contrast, the relaxation time of the electrons is almost insensitive to the lattice disorder, suggesting that the electron transport is unaffected by the lattice disorder though the phonons are strongly scattered.
A TiS2 single crystal can be mechanically cleaved into nanosheets which can be termed as “titanium sulfene”. Seebeck coefficient increases with decreasing thickness of a nanosheet. Band structure calculations indicated the DOS near the conduction band minimum is enhanced by decreasing thickness of a nanosheet, which is beneficial for large Seebeck coefficient. These findings inspired us to construct inorganic/organic superlattices to get high ZT based on the two possible phenomena occurring simultaneously; electron confinement and phonon confinement in a rigid inorganic layer. Accordingly, we have been attempting to intercalate organic compounds into the van der Waals gaps in TiS2, and we will discuss the superlattice formation to achieve high TE performance.
References
1. C. L. Wan, Y. F. Wang, N. Wang, K. Koumoto, Materials, 3, 2606 (2010).
2. C. L. Wan, K. Koumoto et al., Sci. Technol. Adv. Mater., 11, 044306 (2010).
3. C. L. Wan, K. Koumoto et al., J. Electron. Mater., 40, 1271 (2011).
4. C. L. Wan, K. Koumoto et al., Appl. Phys. Lett., 100, 101913 (2012).
5. Y. E. Putri, C. L. Wan, K. Koumoto et al., Scripta Mater., 66, 895 (2012).
6. R. Z. Zhang, C. L. Wan, K. Koumoto, submitted.
Resume （Professor Kunihito Koumoto）
Education
1979.3 The University of Tokyo, Department of Industrial Chemistry, Ph.D. Ceramics major
1976.3 The University of Tokyo, Department of Industrial Chemistry, M.S. Ceramics major
1974.3 The University of Tokyo, Department of Synthetic Chemistry, B.S. Ceramics major
Working Experience
2011.4-2013.3 Nagoya University, Materials Backcast Technology Research Center, Director
2009.4-2011.3 Nagoya University, Materials Backcast Technology Research Center, Deputy Director
2006.4~ Nagoya University, Department of Applied Chemistry,Professor
2004.4-2006.3 Nagoya University, Department of Molecular Design and Engineering, Professor
1992.4-2004.3, Nagoya University, Department of Applied Chemistry, Professor
1986.9-1992.3, The University of Tokyo, Department of Industrial Chemistry, Associate Professor
1982.4-1986.8, The University of Tokyo, Department of Industrial Chemistry, Lecturer
1979.4-1982.3, The University of Tokyo, Department of Industrial Chemistry, Research Associate
Research Interests
Materials science, Solid state chemistry, Thermoelectric materials, Bio-inspired synthesis of inorganic materials, Nanomaterials, etc.
Achievements
350 SCI Journal papers
93 Review Articles
80 Int. Conf. Proceedings papers
50 Books and Book Chapters
91 (English) and 85 (Japanese) invited talks at academic and technical meetings |
