Elucidating the Influence of Local Structure Perturbations on the Metal–Insulator Transitions of V_1–xMo_xO₂ Nanowires: Mechanistic Insights from an X-ray Absorption Spectroscopy Study

Abstract

The substitutional doping of Mo within VO2 substantially alters the electronic and structural phase diagrams of the host lattice, most notably by bringing the technologically relevant metal–insulator phase transition temperature in closer proximity to room temperature. Here, we have used X-ray absorption fine structure (XAFS) spectroscopy at V and Mo K-edges to examine the local electronic and geometric structure of both the dopant atoms and the host lattice. A nominal Mo oxidation state of +5 has been determined, which implies electron doping of the VO2 band structure. In addition, XAFS studies suggest that doping with Mo creates locally symmetric domains that are more akin to the high-temperature rutile phase of VO2, thereby lowering activation energy barriers for structural transformation to the metallic phase. Substantial rectification of octahedral canting is also observed upon Mo doping, which has the effect of decreasing V 3d–O 2p hybridization and likely assists in closing the characteristic band gap of the low-temperature monoclinic phase. A correlated set of cationic interactions is seen to emerge with increasing Mo doping, which can be ascribed to local dimerization along the rutile c axis as has been proposed to be a characteristic structural feature of a correlated metallic phase with intermediate mass.

Unraveling Metal-insulator Transition Mechanism of VO2Triggered by Tungsten Doping

“…At first sight, the LS around W atom highlighted in white exhibits two prominent features: the increased symmetry and the expanded volume. A point worth emphasizing is that several XAFS studies by Patridge et al 23,. Booth et al 12,.…”

Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties

“…The mean phase transition temperature (T t ) is about 54.5°C, which is much lower than that of pure VO 2 films (68°C) deposited by other methods1027. It is known that phase transition temperature can be depressed by doping, finite size and inhomogeneous strain2829. For VO 2 STF without doping, films are porous with tilted columnar structure and the residual stress is huge30.…”

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO2 upon Iridium Doping

“…Such effects can be especially acute for “rugged” energy landscapes characterized by a series of closely related polymorphs. For instance, the introduction of Al and Cr on the vanadium sublattice of VO 2 stabilizes the M 2 polymorph, whereas substitutional W‐ and Mo‐doping on the vanadium sublattice preferentially stabilizes the R polymorph over the M 1 polymorph even rendering the former metallic phase accessible at room temperature . Interstitial B‐doping of VO 2 similarly stabilizes the R polymorph over the M 1 polymorph, thereby strongly depressing the characteristic MIT temperature, whereas in contrast, interstitial H incorporation stabilizes two distinct orthorhombic phases, O 1 and O 2 .…”

“…For instance, the introduction of Al and Cr on the vanadium sublattice of VO 2 stabilizes the M 2 polymorph, [25,26] whereas substitutional W-and Mo-doping on the vanadium sublattice preferentially stabilizes the R polymorph over the M 1 polymorph even rendering the former metallic phase accessible at room temperature. [27][28][29] Interstitial B-doping of VO 2 similarly stabilizes the R polymorph over the M 1 polymorph, [30] thereby strongly depressing the characteristic MIT temperature, whereas in contrast, interstitial H incorporation stabilizes two distinct orthorhombic phases, O 1 and O 2 . [31] In this work, we demonstrate the stabilization of a metastable orthorhombic VO 2 (P) phase with rectangular tunnels upon substitutional Ir doping on the cation sublattice of VO 2 .…”