New metathesis routes to layered dichalcogenides: synthesis, crystal growth and structure of NayNbX2 (y = 0.5, X = S, Se)

Abstract

Separated reactant metathesis methods using ternary oxide precursors and yttrium chalcogenides have been used to prepare powders and crystals of alkali metal niobium dichalcogenides, A_yNbX₂ (X = S, Se). The structure of Na_0.5NbSe₂ has been solved unambiguously for the first time from single crystal X-ray data (hexagonal space group P6₃/mmc (no. 194), a = 3.4762(7), c = 15.342(2) Å, U = 160.55(5) ų, Z = 2). Similarly, the structure of Na_0.5NbS₂ has also been determined (hexagonal space group P6₃/mmc, a = 3.3533(4), c = 14.547(3) Å, U = 141.66(4) ų, Z = 2). Products have been characterised further by powder X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. Magnetic measurements describe temperature-independent paramagnetic behaviour for both dichalcogenides, with no superconducting transitions above 1.8 K.