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

Abstract

Metastable compounds accessible through kinetic stabilization or under conditions of constrained equilibrium represent a richly varied landscape of structures, properties, and function that are oftentimes entirely inaccessible in thermodynamic minima. The multiple redox states of vanadium and the ability to modulate the connectivity of vanadium and oxygen atoms yields a rich diversity of structures for binary vanadium oxides. Here, it is demonstrated that an orthorhombic quasi‐1D polymorph of VO2, characterized by extended tunnels with a rectangular cross‐section, can be stabilized through the substitutional doping of iridium on the vanadium sublattice. The obtained structure is considerably distorted from a previously reported paramontroseite mineral phase. The metastable phase is obtained in nanoplatelet form and is stable with respect to the energetically proximate monoclinic/rutile thermodynamic minima up to a temperature of 350 °C. The open framework structure and the accessibility of multiple redox states at the vanadium center suggests that the polymorph could potentially serve as an intercalation host. Beyond the solubility limit of iridium on the vanadium sublattice (1.28–3.15 at.% depending on the precursor concentration), metallic Ir nanocrystals are found to be homogeneously dispersed on the surfaces of the nanoplatelets indicating a strong interaction between the metal nanocrystals and oxide lattice.

Atomic Hourglass and Thermometer Based on Diffusion of a Mobile Dopant in VO2

“…10,14,15 Other dopants induce the stabilization of altogether different polymorphs; for instance, Cr-and Al-doping (or coherent epitaxial strain) stabilizes the M 2 phase, 16−18 interstitial hydrogen doping stabilizes orthorhombic variants, 19 and Ir doping stabilizes a 1D tunnelstructured phase. 20 The introduction of B atoms as interstitial dopants within VO 2 selectively stabilizes the R phase over the M 1 phase. 21,22 The distinctive location of boron dopants within interstitial sites causes the incorporated boron atoms to be weakly coupled to the anion and cation sublattice imbuing a mobility that results in a dynamical response in the monoclinic phase hitherto not observed for conventional static substitutional dopants.…”

VO2 as a Highly Efficient Electrocatalyst for the Oxygen Evolution Reaction

“…Preparation of VO 2 (M1) nanoparticles f or comparison: VO 2 (M1) nanoparticles were synthesized hydrothermally by adding 300 mg of V 2 O 5 powder (Sigma-Aldrich) and 450 mg of oxalic acid (Fisher Scientific, Waltham, MA, USA) to 16 mL of deionized water (ρ = 18.2 MΩ/cm, purified using a Barnstead International NANOpure Diamond system) in a 23 mL polytetrafluoroethylene cup, as reported in previous work [ 38 ]. The reaction mixture was heated within an autoclave to 250 °C for 72 h. A matte-black powder was collected by vacuum filtration and washed with copious amounts of acetone and deionized water.…”

Thin Film Stabilization of Different VO2Polymorphs

“…In this chapter we will focus on the stabilization of thin film of six main VO 2 polymorphs: VO 2 (M 1 ), VO 2 (M 2 ), VO 2 (R), VO 2 (T), VO 2 (A) and VO 2 (B). But in passing it should be noted that VO 2 polymorphs likewise VO 2 (M 3 ), VO 2 (P), VO 2 (C) and VO 2 (D) have also been mostly studied in bulk and nanostructure form and reports are missing on thin film stabilization of these phases [24][25][26][27][28][29]31]. Space group and lattice parameters of different VO 2 polymorphs known to us are tabulated in Table 1.…”

“…Being a strongly correlated electron system, VO 2 is equally attractive to condensed-matter physicists [19][20][21][22]. VO 2 can exhibit various polymorphic structures (such as: A, B, C, D, M 1 , M 2 , M 3 , P, R and T), each having quite different physical and chemical properties [23][24][25][26][27][28][29][30][31]. Among these polymorphs, many are neither stable in ambient conditions nor can be easily synthesized.…”