Orbital electronic occupation effect on metal-insulator transition in Ti x V1-x O2.

A series of Ti x V1-x O2 (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 (T MIT) of Ti x V1-x O2 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 c r axis while shrinking along the a r and b r 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 T MIT rising. The research reveals that the T MIT 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.