Unraveling Mechanism on Reducing Thermal Hysteresis Width of VO₂ by Ti Doping: A Joint Experimental and Theoretical Study

Tailoring effectively the hysteresis loop width of VO 2 semiconductor-metal transition (SMT) is crucial to develop thermal sensor devices. The Ti-doping is known as the most effective method to reduce Δ T c and has been considered as the prototypical model in understanding the mechanism by which the Δ T c of VO 2 MST could be manipulated. Here we present a joint experimental and first-principles computational study on nondoped and Ti-doped VO 2 to clarify the mechanism of Ti-doping on narrowing the hysteresis loop width of VO 2 . On the basis of the analyses of differential scanning calorimetry (DSC), we found that phase transition temperatures in the cooling circle increase faster than those in the heating circle with increasing Ti concentrations, exhibiting a hysteresis width reduction at 2 °C per Ti at. %. First-principles calculations reveal that dopant Ti atoms break the octahedral symmetry of local structure in VO 2 (R) phase. This distortion is propagated in anisotropy and exhibits an obvious nonlocal effect. In contrast, the Ti-doping-induced structural change in VO 2 (M) phase is only constrained in Ti-involved chain along the a -axis. The calculated energy profiles for Ti x V 1– x O 2 phase transition shows that structural stability and activation energies increased with the increase of Ti concentration. The activation barriers in Ti-doped VO 2 (R) phases are increased more remarkably than that in Ti-doped VO 2 (M) phases, which is consistent with experimental observation of concentration-dependent reduction of thermal hysteresis width.