Coexistence of Direct and Indirect Crystallographic Pathways in Deoxidation of Molybdenum(VI) Oxide Nanowires

Molybdenum oxide (MoO₃)-based materials have attracted considerable attention due to their significant applications in catalysis and optoelectronics. However, the introduction of oxygen vacancies into MoO₃ materials under working conditions inevitably results in drastic changes in their properties and performance. Therefore, it is imperative to comprehend the deoxidation process of MoO₃ in controlled environments. Herein, we reveal the deoxidation mechanisms of orthorhombic MoO₃ using an advanced in situ transmission electron microscopy technique. We found that during heating-induced deoxidation, MoO₃ material can follow two possible crystallographic pathways. The first is a direct topochemical transformation from orthorhombic MoO₃ into monoclinic MoO₂, whereas the other is an indirect transition involving a monoclinic MoO₃ intermediate phase. The coexistence of these two pathways can be explained by the kinetic competition between elemental diffusion and phase transformation. Our findings provide fundamental insight into the deoxidation process of molybdenum oxides and offer potential guidance for their structural design.