Crystal Structure and Thermoelectric Properties of Misfit-Layered Sulfides [Ln2S2] p NbS2 (Ln = Lanthanides)

Polycrystalline samples of misfit-layered sulfides [Ln(2)S(2)] (p) NbS2 (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 [Ln(2)S(2)] 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 cation-deficient samples with Ln = Yb exhibit the highest Seebeck coefficient S a parts per thousand 59 mu V/K. With electrical resistivity of cm and thermal conductivity of kappa = 0.69 W/Km, this yields a dimensionless figure of merit of ZT = 0.11 at 300 K.