Preparation and Thermoelectric Properties of Misfit-Layered Sulfide [Yb1.90S2]0.62NbS2

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We have prepared polycrystalline samples of Yb-Nb-S-based misfit-layered compound and measured their thermoelectric properties below 300 K. The compound consists of an alternate stacking of a trigonal prism (MoS2)-type [NbS2] layer and a two-layered rock-salt-type [Yb1.90S2] slab, being incommensurate parallel to the $a$-axis. Approximately 5% Yb deficiency is necessary to obtain single-phase samples. Metallic conductivity accompanied by a large Seebeck coefficient $S$ has been observed down to 4.2 K for the single-phase samples. At 300 K, the sample exhibits $S = 60$ μV$\cdot$K-1 and resistivity of $\rho = 1.4$ m$\Omega$$\cdot$cm, with thermal conductivity of $\kappa = 0.80$ W$\cdot$K-1$\cdot$m-1. The resulting figure-of-merit ($Z = S^2/\rho\kappa$) becomes $3.2\times 10^{-4}$ K-1 at 300 K, yielding the dimensionless figure-of-merit of $ZT\sim 0.1$.
2004-09-15