skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Friday, September 13 until 2:00 AM ET on Saturday, September 14 due to maintenance. We apologize for the inconvenience.


Title: Decoupling the metal–insulator transition temperature and hysteresis of VO 2 using Ge alloying and oxygen vacancies
The metal-to-insulator transition of VO 2 underpins applications in thermochromics, neuromorphic computing, and infrared vision. Ge alloying is shown to elevate the transition temperature by promoting V–V dimerization, thereby expanding the stability of the monoclinic phase to higher temperatures. By suppressing the propensity for oxygen vacancy formation, Ge alloying renders the hysteresis of the transition exquisitely sensitive to oxygen stoichiometry.  more » « less
Award ID(s):
1545403
NSF-PAR ID:
10347281
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Chemical Communications
Volume:
58
Issue:
46
ISSN:
1359-7345
Page Range / eLocation ID:
6586 to 6589
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    In this work, nine nanocrystalline binary Mg alloys were synthesized by high-energy ball milling. The compositions, Mg-5 wt% M (M-Cr, Ge, Mn, Mo, Ta, Ti, V, Y, and Zn), were milled with the objective of achieving non-equilibrium alloying. The milled alloys were consolidated via cold compaction (CC) at 25°C and spark plasma sintering (SPS) at 300°C. X-ray diffraction (XRD) analysis indicated grain refinement below 100 nm, and the scanning electron microscopy revealed homogeneous microstructures for all compositions. XRD analysis revealed that most of the alloys showed a change in the lattice parameter, which indicates the formation of a solid solution. A significant increase in the hardness compared to unmilled Mg was observed for all of the alloys. The corrosion behavior was improved in all of the binary alloys compared to milled Mg. A significant decrease in the cathodic kinetics was evident due to Ge and Zn additions. The influence of the alloying elements on corrosion behavior has been categorized and discussed based on the electrochemical response of their respective binary Mg alloys. 
    more » « less
  2. Abstract

    Distinct properties of multiple phases of vanadium oxide (VOx) render this material family attractive for advanced electronic devices, catalysis, and energy storage. In this work, phase boundaries of VOxare crossed and distinct electronic properties are obtained by electrochemically tuning the oxygen content of VOxthin films under a wide range of temperatures. Reversible phase transitions between two adjacent VOxphases, VO2and V2O5, are obtained. Cathodic biases trigger the phase transition from V2O5to VO2, accompanied by disappearance of the wide band gap. The transformed phase is stable upon removal of the bias while reversible upon reversal of the electrochemical bias. The kinetics of the phase transition is monitored by tracking the time‐dependent response of the X‐ray absorption peaks upon the application of a sinusoidal electrical bias. The electrochemically controllable phase transition between VO2and V2O5demonstrates the ability to induce major changes in the electronic properties of VOxby spanning multiple structural phases. This concept is transferable to other multiphase oxides for electronic, magnetic, or electrochemical applications.

     
    more » « less
  3. null (Ed.)
    Nowotny chimney ladder (NCL) phases are intermetallic compounds formed by transition metals and metals of groups 13 and 14. This family can be expanded by combining two p-elements from different groups with those transition metals, for which the corresponding binary NCL phases are unknown. In this paper, we present three new compounds in the V-Al-Ge, Nb-Al-Ge, and Nb-Ga-Ge systems related to the TiSi2 structure type (Sp. Gr. Fddd) obtained with the standard ampule technique. The crystal structures of the new compounds were determined using synchrotron powder X-ray diffraction data. A transition to the CrSi2 structure type was detected upon changing the composition from VAl0.72(2)Ge1.28(2) to VAl1.534(3)Ge0.466(3). According to the 18–n rule, all the compounds are metallic conductors, which was supported by the electronic structure calculations. It was shown that the expected energy gap located above the Fermi level in the vanadium-based NCL compound collapsed into a pseudogap upon the replacement of V by Nb. 
    more » « less
  4. Abstract

    Engineering electronic bandgaps is crucial for applications in information technology, sensing, and renewable energy. Transition metal dichalcogenides (TMDCs) offer a versatile platform for bandgap modulation through alloying, doping, and heterostructure formation. Here, the synthesis of a 2D MoxW1‐xS2graded alloy is reported, featuring a Mo‐rich center that transitions to W‐rich edges, achieving a tunable bandgap of 1.85 to 1.95 eV when moving from the center to the edge of the flake. Aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy showed the presence of sulfur monovacancy, VS, whose concentration varied across the graded MoxW1‐xS2layer as a function of Mo content with the highest value in the Mo‐rich center region. Optical spectroscopy measurements supported by ab initio calculations reveal a doublet electronic state of VS, which is split due to the spin‐orbit interaction, with energy levels close to the conduction band or deep in the bandgap depending on whether the vacancy is surrounded by W atoms or Mo atoms. This unique electronic configuration of VSin the alloy gave rise to four spin‐allowed optical transitions between the VSlevels and the valence bands. The study demonstrates the potential of defect and optical engineering in 2D monolayers for advanced device applications.

     
    more » « less
  5. Abstract

    Magnetic skyrmions are topologically protected spin textures that are being investigated for their potential use in next generation magnetic storage devices. Here, magnetic skyrmions and other magnetic phases in Fe1−xCoxGe (x< 0.1) microplates (MPLs) newly synthesized via chemical vapor deposition are studied using both magnetic imaging and transport measurements. Lorentz transmission electron microscopy reveals a stabilized magnetic skyrmion phase near room temperature (≈280 K) and a quenched metastable skyrmion lattice via field cooling. Magnetoresistance (MR) measurements in three different configurations reveal a unique anomalous MR signal at temperatures below 200 K and two distinct field dependent magnetic transitions. The topological Hall effect (THE), known as the electronic signature of magnetic skyrmion phase, is detected for the first time in a Fe1−xCoxGe nanostructure, with a large and positive peak THE resistivity of ≈32 nΩ cm at 260 K. This large magnitude is attributed to both nanostructuring and decreased carrier concentrations due to Co alloying of the Fe1−xCoxGe MPL. A consistent magnetic phase diagram summarized from both the magnetic imaging and transport measurements shows that the magnetic skyrmions are stabilized in Fe1−xCoxGe MPLs compared to bulk materials. This study lays the foundation for future skyrmion‐based nanodevices in information storage technologies.

     
    more » « less