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.

Lead-free halide double perovskite Cs₂CuSbCl₆ nanocrystals have recently been reported to have a low bandgap of 1.66 eV. In this work, we show that the optical absorption spectra and X-ray diffraction patterns previously attributed to Cs₂CuSbCl₆ can rather be explained with Cs₃Sb₂Cl₉:Cu: X-ray absorption spectroscopy identifies [CuCl₃]⁻ trigonal pyramids, with Cu²⁺ possibly replacing two Cs⁺ sites. The broad low-energy optical absorption is then assigned to localized electronic transitions at copper dopants within the Cs₃Sb₂Cl₉ lattice, which do not affect the wide bandgap. Ab initio calculations suggest that Cs₂CuSbCl₆ is thermodynamically unstable with respect to decomposition to Cs₃Sb₂Cl₉, in line with the low reproducibility of Cs₂CuSbCl₆ observed in its synthesis.

The bending strain sensitivity of (TMSO)SnI ₃ , a monodimensional lead-free halide, is greatly increased by Bi doping. The observed piezoresistivity is fully reversible and can be explained based on the microstructural features.

Layered TiS₂ intercalated with linear alkylamines has recently attracted significant interest as a model compound for flexible n-type thermoelectric applications, showing remarkably high power factors at room temperature. The thermal and, particularly, environmental stability of such materials is, however, a still an open challenge. In this paper, we show that amine-intercalated TiS₂ prepared by a simple mechanochemical process is prone to chemical decomposition through sulfur exsolution, and that the presence of molecular oxygen is likely to mediate the decomposition reaction. Through computational analysis of the possible reaction pathways, we propose that Ti-N adducts are formed as a consequence of amine groups substituting for S vacancies on the internal surfaces of the S-Ti-S layers. These findings provide insights for possible future applications of similar hybrid compounds as devices operating in ambient conditions, and suggest isolating them from atmospheric oxygen.