Distinct properties of multiple phases of vanadium oxide (VO
- NSF-PAR ID:
- 10061726
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 28
- Issue:
- 34
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
null (Ed.)Epitaxial films of vanadium dioxide (VO 2 ) on rutile TiO 2 substrates provide a means of strain-engineering the transition pathways and stabilizing of the intermediate phases between monoclinic (insulating) M1 and rutile (metal) R end phases. In this work, we investigate structural behavior of epitaxial VO 2 thin films deposited on isostructural MgF 2 (001) and (110) substrates via temperature-dependent Raman microscopy analysis. The choice of MgF 2 substrate clearly reveals how elongation of V–V dimers accompanied by the shortening of V–O bonds triggers the intermediate M2 phase in the temperature range between 70–80 °C upon the heating–cooling cycles. Consistent with earlier claims of strain-induced electron correlation enhancement destabilizing the M2 phase our temperature-dependent Raman study supports a small temperature window for this phase. The similarity of the hysteretic behavior of structural and electronic transitions suggests that the structural transitions play key roles in the switching properties of epitaxial VO 2 thin films.more » « less
-
Abstract The reactivity of water with Li‐rich layered Li2RuO3and partial exchange of Li2O with H2O within the structure is studied under aqueous (electro)chemical conditions. Upon slow delithiation in water over long time periods, micron‐sized Li2RuO3particles structurally transform from an O3 structure to an O1 structure with a corresponding loss of 1.25 Li ions per formula unit. The O1 stacking of the honeycomb Ru layers is imaged using high‐resolution high‐angle annular dark‐field scanning transmission electron microscopy, and the resulting structure is solved by X‐ray powder diffraction and electron diffraction. In situ X‐ray absorption spectroscopy suggests that reversible oxidation/reduction of bulk Ru sites is realized on potential cycling between 0.4 and 1.25 VRHEin basic solutions. In addition to surface redox pseudocapacitance, the partially delithiated phase of Li2RuO3shows high capacity, which can be attributed to bulk Ru redox in the structure. This work demonstrates that the interaction of aqueous electrolytes with Li‐rich layered oxides can result in the formation of new phases with (electro)chemical properties that are distinct from the parent material. This understanding is important for the design of aqueous batteries, electrochemical capacitors, and chemically stable cathode materials for Li‐ion batteries.
-
Abstract The characteristic metal–insulator phase transition (MIT) in vanadium dioxide results in nonlinear electrical transport behavior, allowing VO2devices to imitate the complex functions of neurological behavior. Chemical doping is an established method for varying the properties of the MIT, and interstitial dopant boron has been shown to generate a unique dynamic relaxation effect in individual B‐VO2particles. This paper describes the first demonstration of an electrically stimulated B‐VO2proto‐device which manifests a time‐dependent critical transformation temperature and switching voltage derived from the coupling of dopant diffusion dynamics and the metal–insulator transition of VO2. During quasi‐steady current‐driven transitions, the electrical responses of B‐VO2proto‐devices show a step‐by‐step progression through the phase transformation, evidencing domain transformations within individual particles. The dynamic relaxation effect is shown to increase the critical switching voltage by up to 41% (Δ
V crit= 0.13 V) and also to increase the resistivity of the M1 phase of B‐VO2by 14%, imbuing a memristive response derived from intrinsic material properties. These observations demonstrate the dynamic relaxation effect in B‐VO2proto‐devices whose electrical transport responses can be adjusted by electronic phase transitions triggered by temperature but also by time as a result of intrinsic dynamics of interstitial dopants. -
Aqueous Zn/MnO 2 batteries with their environmental sustainability and competitive cost, are becoming a promising, safe alternative for grid-scale electrochemical energy storage. Presented as a promising design principle to deliver a higher theoretical capacity, this work offers fundamental understanding of the dissolution–deposition mechanism of Zn/β-MnO 2 . A multimodal synchrotron characterization approach including three operando X-ray techniques (powder diffraction, absorption spectroscopy, and fluorescence microscopy) is coupled with elementally resolved synchrotron X-ray nano-tomography. Together they provide a direct correlation between structural evolution, reaction chemistry, and 3D morphological changes. Operando synchrotron X-ray diffraction and spectroscopy show a crystalline-to-amorphous phase transition. Quantitative modeling of the operando data by Rietveld refinement for X-ray diffraction and multivariate curve resolution (MCR) for X-ray absorption spectroscopy are used in a complementary fashion to track the structural and chemical transitions of both the long-range (crystalline phases) and short-range (including amorphous phases) ordering upon cycling. Scanning X-ray microscopy and full-field nano-tomography visualizes the morphology of electrodes at different electrochemical states with elemental sensitivity to spatially resolve the formation of the Zn- and Mn-containing phases. Overall, this work critically indicates that for Zn/MnO 2 aqueous batteries, the reaction pathways involving Zn–Mn complex formation upon cycling become independent of the polymorphs of the initial electrode and sheds light on the interplay among structural, chemical, and morphological evolution for electrochemically driven phase transitions.more » « less
-
Abstract Organofunctionalized tetranuclear clusters [(MIICl)2(VIVO)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2)}2] (
1 , M=Co,2 : M=Zn) containing an unprecedented oxometallacyclic {M2V2Cl2N4O8} (M=Co, Zn) framework have been prepared by solvothermal reactions. The new oxo‐alkoxide compounds were fully characterized by spectroscopic methods, magnetic susceptibility measurement, DFT and ab initio computational methods, and complete single‐crystal X‐ray diffraction structure analysis. The isostructural clusters are formed of edge‐sharing octahedral {VO5N} and trigonal bipyramidal {MO3NCl} units. Diethanolamine ligates the bimetallic lacunary double cubane core of1 and2 in an unusual two‐mode fashion, unobserved previously. In the crystalline state, the clusters of1 and2 are joined by hydrogen bonds to form a three‐dimensional network structure. Magnetic susceptibility data indicate weakly antiferromagnetic interactions between the vanadium centers [J iso(VIV−VIV)=−5.4(1 ); −3.9(2 ) cm−1], and inequivalent antiferromagnetic interactions between the cobalt and vanadium centers [J iso(VIV−CoII)=−12.6 and −7.5 cm−1] contained in1 .