Thermal Decomposition of Molybdenum(II) Acetate as a Controlled Route to MoO₂ and Mo₂C Nanostructures: Structural,...

Developing reproducible synthetic routes for reduced molybdenum-based nanostructures remains challenging due to the strong sensitivity of Mo-O systems to temperature, processing atmosphere, and precursor chemistry. Here, we demonstrate that the controlled thermal decomposition of molybdenum-(II) acetate under vacuum provides a simple solid-state route for obtaining monoclinic MoO₂ nanoparticles and hexagonal β-Mo₂C with tunable morphology. Structural, morphological, and thermal analyses revealed a three-stage transformation pathway: (i) precursor degradation and amorphization between 300 and 400 °C; (ii) nucleation and crystallization of monoclinic MoO₂ between 500 and 700 °C, yielding spherical nanoparticles with an average diameter of 23 ± 7.9 nm; and (iii) formation of vertically oriented MoO₂/β-Mo₂C microflakes at 800 °C, evidencing nanoparticle coalescence and the partial conversion of MoO₂ into the β-Mo₂C phase. Time-Differential Perturbed Angular Correlation (TDPAC) spectroscopy, using the ¹¹¹In-(¹¹¹Cd) probe, provided atomic-scale information on local electric field gradients, enabling the direct identification of amorphous and crystalline MoO₂ environments while revealing the role of defects, oxygen vacancies, and surface heterogeneities during phase evolution. These findings establish molybdenum-(II) acetate as an effective precursor for the synthesis of molybdenum-based nanostructures and provide a multiscale understanding, spanning atomic to micrometer length scales, of the mechanisms governing the formation of MoO₂ and β-Mo₂C. Furthermore, the results indicate that carbonaceous species generated during precursor decomposition promote a coupled carbothermal reduction-carburization pathway, leading to the formation of β-Mo₂C.