title: Depressed transition temperature of W(x)V(1-x)O2: mechanistic insights from the X-ray absorption fine structure (XAFS) spectroscopy.
abstract: The mechanism for the decreasing critical temperature (T(C)) of the metal-insulator transition (MIT) in vanadium dioxide (VO2) by tungsten (W) doping is a matter of debate. Here, to clarify the correlation between W doping and T(C), the electronic and geometrical structures around W and V atoms in W(x)V(1-x)O2 samples are systematically investigated by X-ray absorption fine structure (XAFS) spectroscopy. The evidence of electron doping of W(6+) ions in VO2 is obtained from the reduction of V(4+) to V(3+) ions. This kind of electron doping has been considered to favor the MIT process. Moreover, from the XAFS results, the local rutile structure around W dopants is identified even at low doping, and acts as the structure-guided domain to facilitate the MIT in VO2. Considering the electronic band structures of W(x)V(1-x)O2 samples, the internal stresses induced by W(6+) doping yield the detwisting of the nearby monoclinic VO2 lattice. This lattice detwisting will drive the downward shift of the π* electron band and a smaller separation between antibonding and bonding d∥ orbitals in the band structure of VO2, which induces the decreased band gaps of W(x)V(1-x)O2 samples. As a consequence, the potential energy barrier for phase transition is lowered and the reduced T(C) is observed.
authors.affiliation: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, 230029, People's Republic of China. czou@ustc.edu.cn.
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Wu
authors.forename: Lele
authors.initials: L
authors.lastname: Fan
authors.forename: Weifeng
authors.initials: W
authors.lastname: Huang
authors.forename: Shuangming
authors.initials: S
authors.lastname: Chen
authors.forename: Shi
authors.initials: S
authors.lastname: Chen
authors.forename: Feihu
authors.initials: F
authors.lastname: Chen
authors.forename: Chongwen
authors.initials: C
authors.lastname: Zou
authors.forename: Ziyu
authors.initials: Z
authors.lastname: Wu