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

Abstract

Abstract The structural aspects of the insulator–metal transition (IMT) characteristics of VO 2 are sensitive to the octahedral symmetry variation of VO 6 . By varying substrate orientation ( c ‐, a ‐, and m ‐plane Al 2 O 3 ), the correlation between IMT temperature and local symmetry is investigated. For a VO 2 film deposited on m ‐plane Al 2 O 3 , which has high symmetry due to fewer domain boundaries induced by m ‐plane Al 2 O 3 , the IMT temperature is low (326.47 K). In contrast, for a film deposited on c ‐plane Al 2 O 3 (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 VO 2 film deposited on c ‐, a ‐, and m ‐plane Al 2 O 3 , 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.