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.