中文摘要：

VO_2是一种热致相变金属氧化物.在341 K附近,VO_2发生由低温绝缘体相到高温金属相的可逆转变,同时伴随着光学、电学和磁学等性质的可逆突变,这种独特的性质使得VO_2在光电开关材料、智能玻璃、存储介质材料等领域有着广阔的应用前景.因此,VO_2金属-绝缘体可逆相变一直是人们的研究热点,但其相变机理至今未有定论.首先,简要概述了VO_2相变时晶体结构和能带结构的变化情况：从晶体结构来讲,相变前后VO_2从低温时的单斜相VO_2（M）转变为高温稳定的金红石相VO_2（R）,在一定条件下此过程也可能伴随着亚稳态单斜相VO_2（B）与四方相VO_2（A）的产生;从能带结构来看,VO_2处于低温单斜相时,其d//能带和π＊能带之间存在一个禁带,带宽约为0.7 eV,费米能级恰好落在禁带之间,表现出绝缘性,而在高温金红石相时,其费米能级落在π＊能带与d//能带之间的重叠部分,因此表现出金属导电性.其次,着重总结了VO_2相变物理机理的研究现状.主要包括：电子关联驱动相变、结构驱动相变以及电子关联和结构共同驱动相变的三种理论体系以及支撑这些理论体系的实验结果.文献报道争论的焦点在于,VO_2是否是Mott绝缘体以及结构相变与金属-绝缘体相变是否精确同时发生.最后,展望了VO_2材料研究的发展方向.

英文摘要：

VO2 is a metal oxide that has a thermally-induced phase-transition. In the vicinity of 341 K, VO2 undergoes a reversible transition from the high-temperature metal phase to the low-temperature insulator phase. Associated with the metal-insulator transition （MIT）, there are drastic changes in its optical, electrical and magnetic characteristics. These make VO2 an attractive material for various applications, such as optical and/or electrical switches, smart glass, storage media, etc. Thus, the reversible metal-insulator phase transition in VO2 has long been a research hotspot. However, the metal-insulator transition mechanism in VO2 has been a subject of debate for several decades, and yet there is no unified explanation. This paper first describes changes of the crystal structure and the energy band structure during VO2 phase transition. With regard to the crystal structure, VO2 transforms from the low-temperature monoclinic phase VO2 （M） into the high-temperature stable rutile phase VO2（R）, and in some special cases, this phase transition process may also involve a metastable monoclinic VO2 （B） phase and a tetragonal VO2（A） phase. In respect of the energy band structure, VO2 undergoes a transition from the low-temperature insulator phase into a high-temperature metal phase. In the band structure of low-temperature monoclinic phase, there is a band gap of about 0.7 eV between d// and π＊ bands, and the Fermi level falls exactly into the band gap, which makes VO2 electronically insulating. In the band structure of high-temperature rutile phase, the Fermi level falls into the overlapping portion of the π＊ and d// bands, which makes VO2 electronically metallic. Next, this paper summarizes the current research status of the physical mechanism underlying the VO2 MIT. Three kinds of theoretical perspectives, supported by corresponding experimental results, have been proposed so far, which includes electron-correlation-driven MIT, Peierls-like structure-driven MIT, and MIT driven by the interpla