Preparation and thermoelectric properties of misfit-layered sulfide [Yb_1.90S₂]_0.62NbS₂

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 [Yb _1.90S₂] 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 300K, the sample exhibits S = 60 μV·K^-1 and resistivity of p = 1.4mΩ·cm, with thermal conductivity of κ = 0.80 W·K^-1·m^-1. The resulting figure-of-merit (Z = S²/ρκ) becomes 3.2 × 10^-4 K^-1 at 300K, yielding the dimensionless figure-of-merit of ZT ∼ 0.1.