Nanostructured tungsten sulfides: insights into precursor decomposition and the microstructure using X-ray scattering methods

Abstract

Herein we present an in-depth study of precursor derived tungsten sulfides, with a focus on their micro- and local structures. We prepared a new tetrathiotungstate based precursor (N₂H₅)₂WS₄ and unveiled the details of its unique decomposition mechanism by a combination of in situ and ex situ analytical techniques. Upon heating the precursor, a new compound with composition (NH₄)(N₂H₅)WS₄ is formed by the decomposition of one hydrazinium molecule. Above ∼190 °C, (NH₄)₂WS₄ crystallized as the second crystalline intermediate followed by successive decomposition to WS₂via amorphous WS₃ upon increasing the temperature. Using X-ray diffraction, total scattering data and pair distribution function (PDF) analyses we are able to develop a detailed picture of the microstructure of nanosized WS₂ samples obtained by the thermal decomposition of the precursor. The microstructure is described by global optimization of the stacking pattern of WS₂ slabs in a supercell containing a large number of layers. The results clearly demonstrate that both stacking faults and random shifts of the WS₂ layers contribute to the disorder in the material. This is significantly distinct to bulk materials, where solely stacking faults with no turbostratic disorder components were found.