Modelling the structural disorder in trigonal-prismatic coordinated transition metal dichalcogenides

Abstract

Trigonal-prismatic coordinated transition metal dichalcogenides (TMDCs) are formed from stacked (chalcogen)–(transition metal)–(chalcogen) triple layers, where the chemical bond is covalent within the triple layers and van der Waals (vdW) forces are effective between the layers. Bonding is at the origin of the great interest in these compounds, which are used as 2D materials in applications such as catalysis, electronics, photoelectronics, sensors, batteries and thermoelectricity. This paper addresses the issue of modelling the structural disorder in multilayer TMDCs. The structural model takes into account stacking faults, correlated displacement of atoms and average crystallite size/shape, and is assessed by simulation of the X-ray diffraction pattern and fitting to the experimental data relative to a powdered sample of MoS2 exfoliated and restacked via lithiation. From fitting, an average crystallite size of about 50 Å, nearly spherical crystallites and a definite probability of deviation from the fully eclipsed atomic arrangement present in the ordered structure are determined. The increased interlayer distance and correlated intralayer and interlayer atomic displacement are attributed to the presence of lithium intercalated in the vdW gap between triple layers (Li/Mo molar ratio of about 0.06). The model holds for the whole class of trigonal-prismatic coordinated TMDCs, and is suitably flexible to take into account different preparation routes.

Structural Features Governing the Near-Edge X-ray Absorption Spectra of Lead Halide Perovskites

“…10 Their rich defect chemistry and ordering in metal cation sites have been recently described in detail. 11,12 X-ray absorption near-edge structure (XANES), possibly with high-energy resolved fluorescence detection (HERFD-XANES), has been proven to be a powerful tool to assess the oxidation state, coordination geometry, and metal−ligand interactions in a wide range of natural and artificial materials, complementing conventional diffraction and electron microscopy techniques. 13−19 In general, near-edge spectra do not suffer from loss of resolution due to thermal or static disorder as much as the extended X-ray absorption fine structure (EXAFS), and their applicability is therefore much broader.…”

“…(TMSO)­PbI 3 and (TMSO) 3 Bi 2 I 9 (with TMSO = trimethylsulfoxonium, (CH 3 ) 3 SO + ) form a solid solution with a monodimensional pseudo-perovskite structure with edge-sharing octahedra containing either Pb 2+ , Bi 3+ , or a metal cation vacancy, the latter being required to keep charge neutrality . Their rich defect chemistry and ordering in metal cation sites have been recently described in detail. , …”