Shaanxi Key Laboratory for Theoretical Physics Frontiers, Institute of Modern Physics, Northwest University, 710069, Xi'an, China.
Centre for Materials Science, School of Chemistry and Physics, Science and Engineering Faculty, Queensland University of Technology, Gardens Point Campus, Brisbane, QLD 4001, Australia.
Phys Chem Chem Phys. 2022 Dec 21;25(1):759-767. doi: 10.1039/d2cp04763b.
The structural phase transition (SPT) and metal-insulator phase transition (MIT) always occur simultaneously upon heating from the low-temperature insulator M phase to the high-temperature metal R phase in vanadium dioxide, and it is still unclear which one of Mott correlation and Peierls distortion plays a decisive role in the thermally induced phase transition (PT) since 1959. Our density functional theory (DFT)-based calculations revealed that the intermediate phase in the PT, the so-called monoclinic metal phase, is a zero indirect band gap semimetal (2/ space group) with a pseudo gap (199 meV). From the M phase to the monoclinic metal phase, the band gap decreases gradually to zero, and the bonding lengths between vanadium-vanadium atoms remain nearly constant. The SPT and MIT from the intermediate structure to the R phase occur simultaneously with a sudden change of bonding lengths between vanadium-vanadium atoms, in which electrons can jump down rather than jump up to the conduction band minimum (CBM) from the valence band maximum (VBM) under thermal fluctuation in order to lower the total energy of the system to push forward the occurrence of PT. The electron jumping does not require additional energy from Coulomb repulsion between electrons even though it is always present. This SPT is a typical Peierls PT or a pseudo Mott PT rather than an actual Mott PT in the each of the two stages. Our conclusions provide a new understanding of SPT and MIT in vanadium dioxide that has been debated for more than 80 years.
在二氧化钒中，从低温绝缘 M 相升温到高温金属 R 相时，结构相变 (SPT) 和金属-绝缘体相变 (MIT) 总是同时发生，自 1959 年以来，仍不清楚是莫特相关作用还是派尔斯畸变在热诱导相变 (PT) 中起决定性作用。我们基于密度泛函理论 (DFT) 的计算表明，PT 中的中间相，即所谓的单斜金属相，是一个零间接带隙半导体（2/空间群），具有赝隙（199 meV）。从 M 相到单斜金属相，带隙逐渐减小到零，而钒-钒原子之间的键长基本保持不变。从中间结构到 R 相的 SPT 和 MIT 同时发生，钒-钒原子之间的键长发生突然变化，在热波动下，电子可以从价带顶 (VBM) 而不是从导带底 (CBM) 向下跃迁，从而降低系统的总能量，推动 PT 的发生。电子跃迁不需要来自电子之间库仑斥力的额外能量，尽管它总是存在。这种 SPT 是一种典型的派尔斯 PT 或伪莫特 PT，而不是两个阶段中每个阶段的实际莫特 PT。我们的结论为二氧化钒中 SPT 和 MIT 的研究提供了新的认识，这一问题已经争论了 80 多年。
