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.