Synthesis of [(SnSe)1.16–1.09]1[(Nb x Mo1–x )Se2]1 Ferecrystal Alloys

Modification of the modulated elemental reactant method allowed the first reported synthesis of quaternary [(MX) z ] m [(T x T′1–x )­X2] n compounds with controlled compositions. Metastable ferecrystal compounds, [(SnSe)1.16–1.09]1[(Nb x Mo1–x )­Se2]1 with x = 0, 0.26, 0.49, 0.83, and 1, were synthesized and characterized by X-ray diffraction, electron probe microanalysis (EPMA), and scanning transmission electron microscopy (STEM). Misfit layer dichalcogenide analogues, showing controlled alloying of the dichalcogenide layers, have not been reported. Changes in lattice parameters, as a function of x, were similar to literature observations for the (Nb x Mo1–x )­Se2 system. The c-lattice parameters of the ferecrystal alloys decreased linearly from 12.53(2) Å for [(SnSe)1.09]1(MoSe2)1 to 12.27(2) Å for [(SnSe)1.16]1(NbSe2)1. The a-lattice parameters of the dichalcogenide constituent increased from 3.329(8) Å for [(SnSe)1.09]1(MoSe2)1 to 3.461(4) Å for [(SnSe)1.16]1(NbSe2)1. The a-lattice parameter of the rocksalt constituent remained constant resulting in a linear increase in misfit parameter with increased Nb content. Temperature dependent electrical resistivity measurements showed a transition from semiconducting to metallic behavior as the Nb content of the alloys increased.