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 (N sub(2) H sub(5))sub(2)WS sub(4) 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 (NH sub(4))(N sub(2)H sub(5))WS sub(4) is formed by the decomposition of one hydrazinium molecule. Above approximately 190 degree C, (NH sub(4)) sub(2) WS sub(4) crystallized as the second crystalline intermediate followed by successive decomposition to WS sub(2) via amorphous WS sub(3) 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 WS sub(2) samples obtained by the thermal decomposition of the precursor. The microstructure is described by global optimization of the stacking pattern of WS sub(2) slabs in a supercell containing a large number of layers. The results clearly demonstrate that both stacking faults and random shifts of the WS sub(2) 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.