A clear experimental explanation of the contribution of Mott and Peierls transitions to the insulator−metal transition (IMT) characteristics in vanadium dioxide (VO 2 ) is still lacking. Examining the crystal and electronic structures of epitaxial VO 2 films grown at various deposition temperatures, a Mott or a Peierls transition was observed. The VO 2 film deposited at 500 °C showed suppressed Peierls transition characteristics because of the large inplane compressive strain in the insulating phase. The VO 2 films deposited at 600 and 650 °C had a higher IMT temperature because of the relaxation of both the in-plane and out-of-plane strain, and there were abundant V 4+ states. Therefore, it was related to a collaborative Mott−Peierls transition. Finally, the VO 2 film deposited at 720 °C showed a suppressed Mott transition because of the abundance of V 3+ states in the insulating phase. Furthermore, an analysis of the electronic structure of the insulating and metallic phases using in situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy provide a complete band diagram to support the above explanation of the deposition-temperature-dependent IMT characteristics.

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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.

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