Probing the role of thermal vibrational disorder in the SPT of VO_2 by Raman spectroscopy

Abstract

Phase competition in transition metal oxides has attracted remarkable interest for fundamental aspects and technological applications. Here, we report a concurrent study of the phase transitions in undoped and Cr-doped VO_2 thin films. The structural, morphological and electrical properties of our films are examined and the microstructural effect on the metal–insulator transition (MIT) are highlighted. We further present a distinctive approach for analyzing the Raman data of undoped and Cr-doped VO_2 thin films as a function of temperature, which are quantitatively correlated to the electrical measurements of VO_2 films to give an insight into the coupling between the structural phase transition (SPT) and the MIT. These data are also combined with reported EXAFS measurements and a connection between the Raman intensities and the mean Debye–Waller factors sigma ^2 is established. We found that the temperature dependence of the sigma _{R}^{2}(V-V) as calculated from the Raman intensity retraces the temperature profile of the sigma _{EXAFS}^{2}(V-V) as obtained from the EXAFS data analysis. Our findings provide an evidence on the critical role of the thermal vibrational disorder in the VO_2 phase transitions. Our study demonstrates that correlating Raman data with EXAFS analysis, the lattice and electronic structural dynamics can be probed.