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

The 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.