Local Probing of Metallic and Mott Insulating Phases of (V 1‐ x Cr x ) ₂ O ₃ by Plasmon Energy

Insulator‐to‐metal transitions in (V 1‐ x Cr x ) 2 O 3 Mott materials can be triggered by adjusting temperature, pressure, and Cr content. Beyond these conventional routes, the insulating phases of these compounds also display an out‐of‐equilibrium insulator‐to‐metal transition under electric pulses, associated with the formation of a percolating metallic pathway within an insulating matrix. This resistive‐switching property holds promise for emerging devices, such as nonvolatile memories and artificial synapses or neurons. However, understanding the microscopic nature of the electrically induced metallic state remains a key challenge. Electron energy‐loss spectroscopy (EELS) in a transmission electron microscope (TEM) is demonstrated here as a sensitive and spatially resolved technique for distinguishing metallic and insulating domains in (V 1‐ x Cr x ) 2 O 3 Mott systems at the nanoscale. Studies on single crystals reveal the existence of a 0.25 eV shift in volume plasmon energy between the paramagnetic metal (PM) and the insulating phases—paramagnetic insulator (PI) and antiferromagnetic insulator (AFI). This shift arises from the unit cell volume expansion occurring at the metal‐to‐insulator transition, which decreases the density of valence electrons. It is further demonstrated that this nanoscale characterization approach can be effectively extended to polycrystalline V 2 O 3 thin films and to memory devices based on (V 1‐ x Cr x ) 2 O 3 .