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The prototype misfit layer compound (SnS)_1.17NbS₂ consists alternatingly of a metallic triatomic NbS₂ layer, in which Nb atoms are sandwiched by S atoms, and an insulating SnS double layer featuring a NaCl-type structure. Here we investigate the effect of lattice misfit on the stability and chemical bonding in the misfit layer compound using a first-principles density functional theory approach. The calculations show that for the (SnS)_1+<i>x</i>NbS₂ approximants, the most stable one has <i>x</i> = 0.167, close to the experimental observations. Charge analysis finds a moderate charge transfer from SnS to NbS₂. Sn or S vacancies in the SnS part affect the electronic properties and interlayer interactions. The obtained information here helps in understanding the mechanism of formation and stability of misfit layer compounds and ferecrystals and further contributes to the design of novel multilayer compounds and emerging van der Waals heterostructures.