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A3: High temperature materials
Materials with phonon-glass electron-crystal (PGEC) behaviour are becoming popular in the thermoelectric field as they are capable of having the electrical conductivity of a crystalline material and the thermal conductivity of an amorphous or a glass like material [1]. Misfit layered compounds obey perfectly this kind of PGEC behaviour and are potential candidates for thermoelectric applications [2]. (LaS)1+mTS2 (T = Cr, Nb) belongs to the misfit layered compound family with a general formula (MX)1+mTX2 (M = Sn, Pb, Bi, Sb, rare earths; X = S, Se; T = Ti, V, Cr, Nb, Ta; and m = 0.07 – 0.28) [3]. In this study we investigated the high-temperature thermoelectric properties of misfit layered n-type (LaS)1.20CrS2 and p-type (LaS)1.14NbS2. The samples were prepared by CS2 sulfurization of 6 h or 12 h duration and then consolidated using pressure-assisted sintering to produce highly and randomly oriented samples with tunable microstructures. The randomly and highly oriented natural superlattices provided ultralow lattice thermal conductivities (as low as ~0.9 W K−1 m−1 and ~0.5 W K−1 m−1, respectively, at 950 K) perpendicular to the pressing axis. The highly oriented texture produced the highest ZT of 0.14 at 950 K among the (LaS)1.20CrS2 system, whereas the weakly/randomly oriented texture produced the highest ZT of 0.15 at 950 K among the (LaS)1.14NbS2 system [4]. The ratio 1+m was also varied for both the systems and it was determined that for m=0.197, a higher ZT of 0.2 can be obtained for the Nb system at 950 K.
References
[1] G.A. Slack, CRC handbook of thermoelectrics (Ed: D.M. Rowe), CRC Press, Boca Raton, 1995, pp. 407–440.
[2] M. Ohta, S. Satoh, T. Kuzuya, S. Hirai, M. Kunii, A. Yamamoto, Acta Mater., 60, 7232 (2012).
[3] G.A. Wiegers, Prog. Solid St. Chem., 24, 1 (1996).
[4] P. Jood, M. Ohta, H. Nishiate, A. Yamamoto, O. Lebedev, D. Berthebaud, K. Suekuni, M. Kunii, Chem. Mater. (DOI: 10.1021/cm5004559)