Correlation between Symmetry and Phase Transition Temperature of VO2 Films Deposited on Al2O3 Substrates with Various Orientations

Abstract

AbstractThe structural aspects of the insulator–metal transition (IMT) characteristics of VO2 are sensitive to the octahedral symmetry variation of VO6. By varying substrate orientation (c‐, a‐, and m‐plane Al2O3), the correlation between IMT temperature and local symmetry is investigated. For a VO2 film deposited on m‐plane Al2O3, which has high symmetry due to fewer domain boundaries induced by m‐plane Al2O3, the IMT temperature is low (326.47 K). In contrast, for a film deposited on c‐plane Al2O3 (having lower symmetry), the IMT temperature is the highest (336.74 K) among the films used in this work. Furthermore, temperature‐dependent Raman spectra reveals that the structural phase transition temperature decreases in the order of the VO2 film deposited on c‐, a‐, and m‐plane Al2O3, suggesting that the symmetrical structure reduces the activation energy for IMT by decreasing thermodynamic energy. These results demonstrate that structural symmetry plays a crucial role in lowering the transition temperature.