Abstract
New niobium-based misfit sulfides [(Ln1/3Sr2/3S)1.5]1.15NbS2 (Ln=Sm, Tb) have been synthesized from a mixture of SrS, Ln2S3, Nb(m), and S in evacuated and sealed silica tubes by annealing at 1000 °C for 144 h under a sulfur partial pressure of 49.3 kPa. The compounds have been characterized by EDX analysis, X-ray single crystal and powder diffraction, electron diffraction, and magnetic susceptibility measurements. Both sulfides have misfit structures with orthorhombic symmetry for the (Ln1/3Sr2/3S)1.5 (Ln=Sm, Tb) and NbS2 subsystems. The lattice parameters for the different subsystems are: for the Sm-based sulfide [(Sm1/3Sr2/3S)1.5]: a=5.7953(9) Å, b=5.8007(5) Å, c=14.957(2) Å and [NbS2]: a=3.3420(7) Å, b=5.8008(5) Å, c=14.955(2) Å, and for the Tb-based sulfide [(Tb1/3Sr2/3S)1.5]: a=5.769(2) Å, b=5.7766(7) Å, c=14.906(2) Å and [NbS2]: a=3.340(1) Å, b=5.7769(8) Å, c=14.905(2) Å. The [(Sm1/3Sr2/3S)1.5]1.15NbS2 crystal structure has been refined from X-ray single crystal data. It belongs to the 1.5Q/1H homologue type where the (Sm1/3Sr2/3S)1.5 part is a three-atoms-thick slab. Sr-cations are mainly located at the exterior of the slab whereas Sm preferably occupy the positions at its center. Both compounds exhibit paramagnetic temperature dependence down to 2 K.
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