氧空穴导致二氧化钒低温相带隙变窄

具有一定能量的光照导致低温绝缘二氧化钒(VO_2)发生绝缘体金属转变.本文通过密度泛函理论的Heyd-Scuseria-Ernzerhof杂化泛函方法对含氧空穴的低温绝缘VO_2非磁M1相进行第一性原理研究.研究发现,含氧空穴的M1的晶格参数几乎不变,但氧空穴附近的长的V—V键长却变短了.进一步研究发现,尽管纯的非磁M1的带隙是0.68 eV,但含O1和O2位的氧空穴非磁M1带隙分别为0.23 eV和0.20 eV,同时含有O1和O2位氧空穴非磁M1带隙为0.15 eV,这很好地解释了实验结果.

Oxygen vacancy induced band gap narrowing of the low-temperature vanadium dioxide phase

Switching of vanadium dioxide (VO₂) from low-temperature insulating phase to high-temperature rutile phase can be induced by photons with a certain energy. Photoinduced insulator-metal transition is found experimentally in VO₂ polycrystalline film by photos with energy even below 0.67 eV. However, insulator-metal transition in single crystal can only be induced when photo energyis above 0.67 eV. In order to understand these experimental phenomena, we make a first-principle study on low-temperature non-magnetic M1 phase of VO₂ with oxygen vacancy by density functional theory calculations based on the Heyd-Scuseria-Ernzerhof screened hybrid functional. According to symmetry, M1 phase has two kinds of different oxygen vacancies, O1 and O2 vacancies. Calculations are made on structures and electronic properties of nonmagnetic M1 phases with O1 and O2 vacancies, respectively. The present theoretical results show that neither the short vanadium-vanadium (V–V) bond length near O1 or O2 vacancy nor the lattice parameters almost change but the long V–V bond length near O1 or O2 vacancy decreases due to the oxygen vacancy. The long V–V bond lengths near O1 and O2 vacancies are about 2.80 Å and 2.95 Å, respectively, but the long V–V bond length is 3.17 Å in pure M1. The insulating band gap is opened between V 3d bands, and hybridization happens between V 3d and O 2p orbitals. Furthermore, the present theoretical results demonstrate that the band gap of pure nonmagnetic M1 is 0.68 eV while M1 with O1 vacancy, O2 vacancy, and two oxygen vacancies including O1 and O2, have band gaps of 0.23 eV, 0.20 eV, and 0.15 eV, respectively. The band gap decreases probably because oxygen vacancy results in the decease of the long V–V bond length near it. The present results can explain the experimental results well.