Crystal Structure and Thermoelectric Properties of Misfit-Layered Sulfides [Ln2S2]pNbS2 (Ln = Lanthanides)

Polycrystalline samples of misfit-layered sulfides [Ln2S2]pNbS2 (Ln = lanthanides) have been prepared using the CS2 sulfidation method. Except for Ln = Eu and Lu, single-phase samples were prepared. The compounds consist of an alternate stacking of a trigonal prism-type [NbS2] layer and a double-layered NaCl [rock salt (RS)]-type [Ln2S2] block, parallel to the c-axis. Three types of stacking modes of the [NbS2] layer and the RS-type block have been confirmed with a (3 + 1)-dimensional superspace group description: two face-centered orthorhombic structures and one face-centered monoclinic structure. Slightly cationdeficient samples with Ln = Yb exhibit the highest Seebeck coefficient S 59 lV/K. With electrical resistivity of q 1⁄4 1:4 mX cm and thermal conductivity of j = 0.69 W/Km, this yields a dimensionless figure of merit of ZT = 0.11 at 300 K.