Unraveling the growth mechanism of W18O49 nanowires on W surfaces

Abstract

Understanding the growth mechanism is crucial for controlling the morphology and further designing efficient nanostructured materials. Non-stoichiometric tungsten oxides, in particular, W₁₈O₄₉ nanostructures have shown their prominence for various functional applications. This work presents the growth mechanism of W₁₈O₄₉ nanowires on W surfaces under H₂O(v) atmosphere. The phase evolutions are unfolded in view of the detailed thermodynamic considerations. The reaction between W and H₂O(v) produces WO₃ along with H₂ as a by-product. H₂ acts as a reductant for WO₃ and facilitates the W₁₈O₄₉ phase formation. The complete crystallographic relation of the phase transformation could be represented as W(110)//WO₃(010)//W₁₈O₄₉(010). The oxygen vacancy-induced planar defects are responsible for the 1d [010] growth of W₁₈O₄₉ NWs. The hexagonal tunnels along the NW length create a passage for H₂O(v) to repeat the reaction and increase the NW length.