Manipulating the metal-to-insulator transitions of VO2 by combining compositing and doping strategies.

Vanadium dioxide (VO2) exhibits the most abrupt metal-to-insulator transition (MIT) property near room temperature among the representative 3d-orbital correlated oxides, and its structural variation during the MIT usually results in poor mechanical properties as bulk pellets. Moreover, compositing with highly resistive oxides has been reported to improve the mechanical strength of bulk VO2 since the generation and propagation of microcracks is suppressed upon thermocycling across the MIT; further, their respective impacts on electrical transportation are yet unclear. Herein, we demonstrate the role of these highly resistive oxide composites (e.g., HfO2, CoO and Al2O3) in reducing charge leakage along the microcracks within the insulating phase of VO2, leading to more abrupt MIT properties from the perspective of electrical transportation. This enables the possibility of simultaneously regulating the critical temperature and abrupt MIT transition, as well as the mechanical properties of the VO2 bulk pellets via compositing with oxides with different melting points using spark plasma-assisted reactive sintering (SPARS).

Revealing the Role of Hydrogen in Electron-Doping Mottronics for Strongly Correlated Vanadium Dioxide.

Hydrogen-associated electron-doping Mottronics for d-band correlated oxides (e.g., VO2) opens up a new paradigm to regulate the electronic functionality via directly manipulating the orbital configuration and occupancy. Nevertheless, the role of hydrogen in the Mottronic transition of VO2 is yet unclear because opposite orbital reconfigurations toward either the metallic or highly insulating states were both reported. Herein, we demonstrate the root cause for such hydrogen-induced multiple electronic phase transitions by 1H quantification using nuclear reaction analysis. A low hydrogenation temperature is demonstrated to be vital in achieving a large hydrogen concentration (nH ≈ 1022 cm-3) that further enhances the t2g orbital occupancy to trigger electron localizations. In contrast, elevating the hydrogenation temperatures surprisingly reduces nH to ∼1021 cm-3 but forms more stable metallic H0.06VO2. This leads to the recognition of a weaker hydrogen interaction that triggers electron localization within VO2 via Mottronically enhancing the orbital occupancies.