Divergent Phase Evolution in Mixed Oxide W₀.₅Mo₀.₅O₃ under Electron Beam Irradiation and Thermal Annealing

Abstract

Mixed metal oxides such as W 0.5 Mo 0.5 O 3 offer a unique platform for tailoring structural and electronic properties through the synergistic integration of tungsten and molybdenum oxides, yet their phase transformation pathway is poorly understood. Here, we investigate the real-time structural evolution of W 0.5 Mo 0.5 O 3 using advanced in situ transmission electron microscopy (TEM). By decoupling electron-beam irradiation from thermal excitation, two distinct transformation pathways are identified. Under continuous electron irradiation at ambient temperature, orthorhombic W 0.5 Mo 0.5 O 3 undergoes topotactic dehydration and transforms into a hexagonal phase before complete amorphization at a critical dose of 2.45 × 10⁸ e⁻ nm⁻² due to radiolysis. Conversely, in situ thermal annealing up to 1200 °C facilitates a controlled reduction process. While the initial dehydration mirrors the beam-induced pathway, elevated temperatures (>600 °C) trigger the nucleation of oxygen-deficient mixed-metal oxide phase.High-resolution TEM, STEM-EDS mapping and EELS analysis confirm the formation of an orthorhombic Mo 2 W 2 O 11 framework that maintains 1:1 W: Mo atomic ratio. Remarkably, this phase remains crystalline and unexpectedly stable at 1200 °C, far above the reported melting range of molybdenum oxides. These findings provide a quantitative framework for understanding radiation limits in 2D-layered oxides and offer a strategic route for synthesizing thermally robust metastable phases for electrochromic and energy-storage applications.