Orbital electronic occupation effect on metal–insulator transition in TixV1−xO2

Abstract

A series of TixV1−xO2 (0% ⩽ x ⩽ 4.48%) thin films on c-plane sapphire substrates have been fabricated by co-sputtering oxidation solutions, and the metal–insulator transition temperature (TMIT) of TixV1−xO2 films rises monotonically at the rate of 1.64 K/at.% Ti. The x-ray diffraction measurement results show that, after Ti4+ ion doping, the rutile structure expands along the cr axis while shrinking along the ar and br axis simultaneously. It makes the V–O bond length shorter, which is believed to upshift the π* orbitals. The rising of π* orbitals in Ti-doped VO2 has been illustrated by ultraviolet–infrared spectroscopy and first-principles calculation. With the Ti4+ ion doping concentration increasing, the energy levels of π* orbitals are elevated and the electronic occupation of π* orbitals decreases, which weakens the shielding for the strong electron–electron correlations in the d|| orbital and result in the TMIT rising. The research reveals that the TMIT of VO2 can be effected by the electronic occupancy of π* orbitals in a rutile state, which is helpful for developing VO2-based thermal devices.