There has been long-standing interest in tuning the metal-insulator phase transition in vanadium dioxide (VO) via the addition of chemical dopants. However, the underlying mechanisms by which doping elements regulate the phase transition in VO are poorly understood. Taking advantage of aberration-corrected scanning transmission electron microscopy, we reveal the atomistic origins by which tungsten (W) dopants influence the phase transition in single crystalline WVO nanowires. Our atomically resolved strain maps clearly show the localized strain normal to the (122¯) lattice planes of the low W-doped monoclinic structure (insulator). These strain maps demonstrate how anisotropic localized stress created by dopants in the monoclinic structure accelerates the phase transition and lead to relaxation of structure in tetragonal form. In contrast, the strain distribution in the high W-doped VO structure is relatively uniform as a result of transition to tetragonal (metallic) phase. The directional strain gradients are furthermore corroborated by density functional theory calculations that show the energetic consequences of distortions to the local structure. These findings pave the roadmap for lattice-stress engineering of the MIT behavior in strongly correlated materials for specific applications such as ultrafast electronic switches and electro-optical sensors.
KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: R.S.Y. acknowledges financial support from the National Science Foundation (Award No. CMMI-1200383). The acquisition of the UIC JEOL JEM-ARM200CF is supported by an MRI-R2 grant from the National Science Foundation (Grant No. DMR-0959470). Support from the UIC Research Resources Center is also acknowledged. G.M.O. would like to acknowledge the use of SUPERIOR, a high-performance computing cluster at Michigan Technological University. P.M. and S.B. acknowledge support from the National Science Foundation under IIP 1311837 and from the Research Corporation for Science Advancement through a Cottrell Scholar Award. S.S. and G.S. are supported by National Science Foundation (DMR 0847324).