Orbital electronic occupation effect on metal-insulator transition in Ti V O.

A series of Ti V O (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 ) of Ti V O films rises monotonically at the rate of 1.64 K/at.% Ti. The x-ray diffraction measurement results show that, after Ti ion doping, the rutile structure expands along the c axis while shrinking along the a and b 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 VO has been illustrated by ultraviolet-infrared spectroscopy and first-principles calculation. With the Ti 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 rising. The research reveals that the T of VO can be effected by the electronic occupancy of π orbitals in a rutile state, which is helpful for developing VO-based thermal devices.