Micro X-Ray Diffraction Study of VO$_{2}$ Films -- Separation between Metal-Insulator Transition and Structural Phase Transition

It has been well-known that VO$_{2}$ undergoes both a structural phase transition (SPT) from monoclinic (insulator phase) to tetragonal (metal phase) and a discontinuous first-order metal-insulator transition (MIT) (Jump) near 68$^{o}$C. When the MIT and the SPT occurs simultaneously, the MIT can be regarded as the Peierls transition. When both take place separately, the MIT can be interpreted as the Mott transition. Peierls transiton and Mott transition in VO$_{2}$ remain controversial. We have investigated a relation of the MIT and the SPT which are simultaneously measured by I-V measurement and synchrotron micro X-ray of the 1B2 line in Pohang accelerator Lab., respectively. A used sample is a VO$_{2}$-based two terminal device. The result shows that the MIT and the SPT does not occur simultaneously. (References on the MIT: New J. Phys. 6 (1994) 52 (http://www.njp.org), Appl. Phys. Lett. 86 (2005) 242101, Physica B 369 (2005) 76, Phy. Rev. Lett. 97 (2006) 266401, Appl. Phys. Lett. 90 (2007) 023515).