Understanding the kinetic process during the metal-insulator transition is crucial to sort out the underlying physical nature of electron-lattice interactions in correlated materials. Here, based on the temperature-dependent in situ x-ray absorption fine structure measurement and density-functional theory calculations, we have revealed that the monoclinic-to-tetragonal phase transition of VO2 near the critical temperature is characterized by a sharp decrease of the twisting angle δ of the nearest V–V coordination. The VO2 metallization occurs in the intermediate monocliniclike structure with a large twist of V–V pairs when the δ angle is smaller than 1.4º. The correlation between structural distortion and electronic structure points out that the structural rearrangement is a key factor to narrow the insulating band gap.

Fig. 1. (a) The experimental setup of the temperature-dependent in situ XAFS and XRD. V K-edge EXAFS oscillations χ(k) (b) and their Fourier transforms (c) at several temperatures during the heating process.

Fjg. 2  . (a) The initial monoclinic phase, (b) the intermediate structure during the heating process, and (c) the final tetragonal phase. The θT1 in the tetragonal phase evolve from the θ1 and θ2 angles of the monoclinic phase. For the sake of simplicity, the V atom is fixed relatively to the adjacent O and V atoms.