Structural Evolution of CoMoO₄ under Pressure: Multiphase Transformations and Reconstructive Behaviors

Binary transition metal molybdates are of significant research interest due to their distinctive properties, structural diversity, and promising applications. However, comprehensive investigations into the high-pressure structural behaviors and phase transition resistance of their multiphase forms are limited. This study examines the structural characteristics of the representative isostructural molybdate CoMoO₄ under high pressure, using a diamond anvil cell combined with in situ laboratory Raman spectroscopy, X-ray diffraction, and synchrotron radiation X-ray diffraction techniques. β-CoMoO₄ was found to undergo two gradual phase transitions up to 28 GPa, with the strip-shaped, thin samples exhibiting enhanced structural resistance compared to previous compression studies. The initial transition to the α-phase was initiated at a relatively low pressure of approximately 1 GPa. A subsequent phase transition is observed, likely marking the emergence of a high-pressure phase (HP-phase) around 12 GPa, which then becomes the main phase at approximately 17-18 GPa with pronounced hysteresis. Upon pressure release from above 20 GPa, CoMoO₄ predominantly reverts to the β-phase, with only a trace amount of the HP-phase retained. This study elucidates the pressure-induced structural reconstruction of thin CoMoO₄ across its two-stage phase transitions, thereby enriching the fundamental understanding of binary transition metal molybdates under extreme conditions.