Intercalation-dependent elastic properties of transition metal dichalcogenides

Abstract

We present a first-principles study into the elastic behaviour of layered TMDCs and their lithium- or magnesium-intercalated structures. Assessment of the elastic matrices allow us to evaluate key properties such as the bulk, shear, and Young's moduli. These show a general increase with the addition of an intercalant species, though TMDCs composed of later Group transition metals break this trend. We also assess elastic ratios which describe the ductility of a material, allowing us to conclude that the pristine materials are brittle, but become more ductile with the addition of lithium or magnesium. The anisotropy of these materials is also assessed using a combination of the universal anisotropy metric and a direct calculation of the angular dependence of the Young's modulus. The pristine van der Waals materials demonstrate a high degree of anisotropy due to their relatively weak interactions across the vdW spacing, but the introduction of an ion within the vdW region reduced this anisotropy. Finally, we have also explored the elastic properties of intermediate intercalant concentrations for selected systems, where we conclude that different intercalant configurations or the use of multivalent intercalant species can cause significant deviations from commonly-used linear extrapolations.