Revealing the Role of Isovalent Ti-Substitution to Protonation-Triggered Mottronic Transition of VO ₂

Manipulating the strength of the electron correlation stemming from d-orbital electron occupancy enables the tunability of the electronic band structure and transport properties of transition metal oxides, beyond that of conventional semiconductors, even via isovalent elementary substitutions. While the isovalent Ti4+-substitution of vanadium dioxides (VO2) results in intriguing adjustments in metal to insulator transitions, leading to considerable debates, its impact on the protonation-induced Mottronic behaviors of VO2 is completely unknown. Herein, we demonstrate the role of isovalent Ti-substitution in regulating protonation-induced Mottronic transition of V1–xTixO2. Quantitative analysis of the incorporated 1H concentration within V1–xTixO2 via nuclear reaction analysis (NRA) indicates that Ti-substitution suppresses the kinetic 1H incorporation and thereby the Mottronic functionality. It unveils that incorporating sufficient 1H composition is critical to arouse strong electron localization in the Mottronic phase of hydrogenated VO2.