Ordering phenomena in ternary transition-metal dichalcogenides: Critical role of lattice symmetry and vdW interaction

Concentrated solid solution materials with huge compositional design space and normally unexpected property attract extensive interests of researchers. In these emerging materials, local composition fluctuation such as short-range order (SRO), has been observed and found to have nontrivial effects on material properties, and thus can be utilized as an additional degree of freedom for material optimization. To exploit SRO, its interplay with factors beyond element-level property, including lattice symmetry and bonding environment, should be clarified. In this work by using layered transition-metal dichalcogenide Mo(X_0.5X′_0.5)₂ (X/X′ = O, S, Se, or Te) with mixed element in the non-metal sublattice as the platform, the ordering phenomena are systematically studied using multiscale simulations. As expected, electronegativity difference between X and X′ strongly regulates SRO. Additionally, SRO and long-range order (LRO) are observed in the 2H and T/T′ phase of MoXX′, respectively, indicating a strong influence of lattice symmetry on SRO. More importantly, as vdW interaction is introduced, the SRO structure in 2H-MoXX′ bilayer can be re-configured, while the LRO in T/T′-MoXX′ remains unchanged. Electronic insights for SRO and the resultant property variation are obtained. This work presents a thorough understanding of SRO in bonding complex systems, benefiting the SRO-guided material designs.