Synthesis of High Entropy Sulphide and Oxide Powders and Thin Films Using Single Source Molecular Precursors

Abstract

High entropy metal chalcogenides are novel materials incorporating 5 or more elements within a disordered sub-lattice. These materials are stabilised by their inherently high configurational entropy. Recently, high entropy chalcogenides become an area of significant interest for renewable energy applications such as electrocatalysis and thermoelectrics. However, the synthesis of such materials has been challenging. Long time or high temperature is needed to produce a phase pure high entropy metal chalcogenide. Bulk high entropy zinc sulphide analogues containing four, five, and seven metals were synthesised by a single source molecular precursor approach. Both transition and main group metal dithiocarbamate complexes were decomposed simultaneously with a rapid (1 h) and low temperature (500 °C) annealing process, resulting in the formation of high entropy and entropy stabilised metal sulphide powders. These materials were characterised by powder XRD, SEM, TEM and EDX conducted with both SEM and STEM. The entropy stabilized (MnZnInGaCoCuAg)S exhibited remarkable electrocatalytic activity for the hydrogen evolution reaction when combined with conducting carbon black. This hybrid material demonstrated a low onset overpotential of approximately 80 mV and an overpotential of about 255 mV at a current density of 10 mA/cm², underscoring its potential significance in electrochemical applications. The single source molecular precursor approach was further expanded to deposit high entropy sulphide thin films by aerosol assisted chemical vapour deposition. Five metal dithiocarbamates (Zn, In, Ga, Co and Cu dithiocarbamates) were dissolved simultaneously in 10 mL of tetrahydrofuran. The solution was employed to produce an aerosol which was deposited onto glass substrates, forming phase pure (ZnInGaCoCu)S thin films with a chalcopyrite crystal structure. The thin films were analysed by XRD, SEM, TEM, EDX, XPS, Raman spectroscopy and UV-Vis spectroscopy. An elemental composition change was observed along the film and a bandgap of 1.9 eV was measured. The (ZnInGaCoCu)S thin films deposited by AACVD was transformed to a phase pure (ZnInGaCoCu)O by thermal oxidation in air. In-situ XRD found a 2-step transition happening at 550 °C and 750 °C, producing a cubic and rhombohedral oxide material, respectively. Both transitions were directly observed by in-situ STEM and EDX.

Date of Award	31 Dec 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Saunders (Supervisor) & David Lewis (Supervisor)