Electrolytes are characterized by their ionic conductivity (s i ). It is desirable that overall s... more Electrolytes are characterized by their ionic conductivity (s i ). It is desirable that overall s i results from the dominant contribution of the ions of interest (e.g. Li 1 in lithium ion batteries or LIB). However, high values of cationic transference number (t 1 ) achieved by solid or gel electrolytes have resulted in low s i leading to inferior cell performances. Here we present an organogel polymer electrolyte characterized by a high liquid-electrolyte-level s i (,10 1 mS cm 21 ) with high t 1 of Li 1 (.0.8) for LIB. A conventional liquid electrolyte in presence of a cyano resin was physically and irreversibly gelated at 606C without any initiators and crosslinkers, showing the behavior of lower critical solution temperature. During gelation, s i of the electrolyte followed a typical Arrhenius-type temperature dependency, even if its viscosity increased dramatically with temperature. Based on the Li 1 -driven ion conduction, LIB using the organogel electrolyte delivered significantly enhanced cyclability and thermal stability.
Excellent energy storage performance of (Sc0.5Ta0.5)4+ modified (Bi0.5Na0.5)TiO3-based ceramics modulated by the evolution of polar phases
Journal of Materials Chemistry A
An ultrahigh energy storage performance is achieved in the BNST-20% (Sc0.5Ta0.5)4+ ceramic via ch... more An ultrahigh energy storage performance is achieved in the BNST-20% (Sc0.5Ta0.5)4+ ceramic via chemical modification, which could induce the evolution of oxygen vacancies and local polar phases to achieve a high saturation polarization.
Itinerant Semiconducting Antiferromagnetism in Metastable V 3 Ga
physica status solidi (RRL) – Rapid Research Letters, 2019
Herein, a metastable phase of β‐W type V3Ga is identified to exhibit an itinerant semiconducting ... more Herein, a metastable phase of β‐W type V3Ga is identified to exhibit an itinerant semiconducting antiferromagnetism. Density functional theory plus Hubbard U (DFT+U) calculations predict the β‐W type structure as a possible metastable phase, although energetically less favorable than the previously known D03 phase, which is successfully synthesized with good crystallinity by alternating evaporation method with postannealing process rather than traditional coevaporation method. Such a metastable β‐W phase results in an antiferromagnetic (AFM) order up to at least 500 K and highly conductive semiconducting behavior. The antiferromagnetism in the β‐W type V3Ga can be understood in terms of strong Coulomb repulsion and Hund's rule coupling between the nearest neighbor V 3d orbital states and their covalent bonding with the Ga 4p orbitals. These results are further verified by an exchange bias phenomenon revealed in antiferro/ferromagnet hybrid heterostructure of V3Ga and Fe films, where the strong hybridization between Fe 3d and V 3d orbital states at the interface gives rise to the robust perpendicular magnetic anisotropy therein. Herein, a novel route is used to prepare an AFM semiconductor material for antiferromagnet spintronics.
ZnO microrods were grown on glass substrates by the spray pyrolysis method and boron was doped in... more ZnO microrods were grown on glass substrates by the spray pyrolysis method and boron was doped into the ZnO microrods by diffusion. X-ray diffraction results confirmed that the incorporation of B leads to a slight reduction in the deposit texture. Scanning electron microscopy measurements showed that the morphology of the ZnO samples changed from a microrod to nanocrystalline structure with B-doping. Photoluminescence data indicate that Bdoping leads to a relative increase of the unstructured green band intensity. Magnetic measurements revealed that B-doped ZnO samples exhibited room temperature ferromagnetism related to defects, in agreement with first principles theoretical calculations.
Observation of room temperature ferromagnetism in pure La2O3 nanoparticles
Applied Physics A, 2014
ABSTRACT In this paper, we report the observation of intrinsic room temperature ferromagnetism in... more ABSTRACT In this paper, we report the observation of intrinsic room temperature ferromagnetism in pure La2O3 nanoparticles. Magnetism measurement indicates that all of the samples exhibit room temperature ferromagnetism and the saturation magnetization for the samples decreases with the increase in annealing temperature from 700 to 1,000 °C. X-ray photoelectron spectroscopy identifies the presence of oxygen vacancies in the La2O3 nanoparticles. The fitting results of the O 1s spectrum indicate that the variation of the oxygen vacancy concentration is in complete agreement with the change of the saturation magnetization. It is also found that the saturation magnetization of the La2O3 nanoparticles can be tuned by post-annealing in argon or oxygen atmosphere. These results suggest that the oxygen vacancies are largely responsible for the room temperature ferromagnetism in pure La2O3 nanoparticles.
Bulletin of the American Physical Society, Mar 2, 2015
First principles studies of the stability and Shottky barriers of metal/CdTe(111) interfaces ZHEN... more First principles studies of the stability and Shottky barriers of metal/CdTe(111) interfaces ZHEN LIU
The inclusion of heptagonal, octagonal, or larger rings in an sp 2 -bonded carbon network introdu... more The inclusion of heptagonal, octagonal, or larger rings in an sp 2 -bonded carbon network introduces negative Gaussian curvature that can lead to a high network porosity. Here we investigated a particular negatively curved nonplanar sp 2 -carbon structure namely 688P schwarzite, with a view toward the possible use of negatively curved carbons as lithium ion battery anodes. Our first principles calculations show that the presence of pores in schwarzites can lead to three-dimensional Li ion diffusion paths with relatively small energy barriers. We calculated the binding energy of Li (which donates 1 electron to the schwarzite) in different positions in the schwarzite structure, and the open-circuit voltage (OCV) with respect to Li metal and found that this schwarzite has a positive OCV for a Li concentration as high as LiC 4 . The advantages of the particular schwarzite studied here for use as an anode are expected to be present in other sp 2 -bonded carbon networks that feature large polygonal rings.
Catalytic Transparency of Hexagonal Boron Nitride on Copper for Chemical Vapor Deposition Growth of Large-Area and High-Quality Graphene
ACS Nano, Jun 2, 2014
Graphene transferred onto h-BN has recently become a focus of research because of its excellent c... more Graphene transferred onto h-BN has recently become a focus of research because of its excellent compatibility with large-area device applications. The requirements of scalability and clean fabrication, however, have not yet been satisfactorily addressed. The successful synthesis of graphene/h-BN on a Cu foil and DFT calculations for this system are reported, which demonstrate that a thin h-BN film on Cu foil is an excellent template for the growth of large-area and high-quality graphene. Such material can be grown on thin h-BN films that are less than 3 nm thick, as confirmed by optical microscopy and Raman spectroscopy. We have evaluated the catalytic growth mechanism and the limits on the CVD growth of high-quality and large-area graphene on h-BN film/Cu by performing Kelvin probe force microscopy and DFT calculations for various thicknesses of h-BN.
A class of double-perovskite compounds display fast oxygen ion diffusion and high catalytic activ... more A class of double-perovskite compounds display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while maintaining excellent compatibility with the electrolyte. The astoundingly extended stability of NdBa 1Àx Ca x Co 2 O 5+d (NBCaCO) under both air and CO 2containing atmosphere is reported along with excellent electrochemical performance by only Ca doping into the A site of NdBaCo 2 O 5+d (NBCO). The enhanced stability can be ascribed to both the increased electron affinity of mobile oxygen species with Ca, determined through density functional theory calculations and the increased redox stability from the coulometric titration.
Development of Double-Perovskite Compounds as Cathode Materials for Low -Temperature Solid Oxide ... more Development of Double-Perovskite Compounds as Cathode Materials for Low -Temperature Solid Oxide Fuel Cells. -NdBa 1-xCaxCo2O5+ (x = 0, 0.25) are prepared by a glycine-nitrate combustion process using an aqueous solution of stoichiometric amounts of Nd( , and a proper amount of glycine. After combustion, the resulting fine powder is calcined in air (900 C, 4 h). For electrical conductivity measurements, the powder is pressed into pellets and sintered in air (5 MPa, 1150 C, 12 h). The extended stability of NdBa 1-xCaxCo2O5+ under both air and CO2-containing atmosphere is reported along with an excellent electrochemical performance by only Ca doping into the A-site of NdBaCo 2O5+. The maximum power density of a Ca modified SOFC is 2.114 W/cm 2 at 600 C at a high stability of 150 h at 550 C. The enhanced stability is attributed to both the increased electron affinity of mobile O species with Ca and the increased redox stability. -(YOO, S.;
Herein, we demonstrate a preferable synthetic route to transform sp 2 graphene layers into nanosc... more Herein, we demonstrate a preferable synthetic route to transform sp 2 graphene layers into nanoscale-thick diamond nanostructures. The ultrathin purely sp 3 bonded carbon diamond can be easily produced through the functionalization of the outer wall of graphene layers on a metal surface without the need of so called high pressure and high temperature (HPHT) circumstance. The resulting ultrathin sp 3 carbon films are not only diamond per se, but rather are a new material that is only of order ~1 nanometer in thickness. This approach is also applicable to a hexagonal layered boron nitride.
The conversion of multilayer graphenes into sp 3 -bonded carbon films on metal surfaces (through ... more The conversion of multilayer graphenes into sp 3 -bonded carbon films on metal surfaces (through hydrogenation or fluorination of the outer surface of the top graphene layer) is indicated through first-principles computations. The main driving force for this conversion is the hybridization between sp 3 orbitals and metal surface d z 2 orbitals. The induced electronic gap states and spin moments in the carbon layers are confined in a region within 0.5 nm of the metal surface. Whether the conversion occurs depend on the fraction of hydrogenated (fluorinated) C atoms at the outer surface and on the number of stacked graphene layers. In the analysis of the Eliashberg spectral functions for the sp 3 carbon films on a metal surface that is diamagnetic, the strong covalent metal-sp 3 carbon bonds induce soft phonon modes that predominantly contribute to large electron-phonon couplings, suggesting the possibility of phonon-mediated superconductivity. Our computational results suggest a route to experimental realization of large-area ultrathin sp 3 -bonded carbon films on metal surfaces. We first investigated the effect of hydrogenation or fluorination on the free surface of the AB-stacked (Bernal-type stacking) bilayer graphene. Simulating experimental generation of gas phase atoms , hydrogen or fluorine atoms were considered to be available on the surface. Figure is a schematic of the bilayer graphene before the adsorption of such gas atoms (denoted by I). Experimental studies reported that the hydrogen chemisorption coverage of a single-layer graphene is less than half of the carbon atoms 20 . It was however suggested that bilayer or
We predict that biaxial strain of several percent has a colossal effect on the magnetic anisotrop... more We predict that biaxial strain of several percent has a colossal effect on the magnetic anisotropy of ultrathin Fe/XTiO 3 (X=Sr, Ba) bilayers grown epitaxially on appropriate substrates. We demonstrate for the first time that under large compressive biaxial strain the Fe film undergoes an into out-of-plane spin reorientation via ferroelectric polarization switching, where the critical strain depends on the Fe film thickness. The underlying mechanism is the interplay between the strain-enhanced magnetoelectric coupling associated with the enhanced polarization in the ferroelectric substrate and the strain-reduced magnetic anisotropy energy of the Fe overlayer. These findings open interesting prospects for exploiting stain engineering to harvest higher electric field efficiency of magnetic anisotropy for the next generation of MeRAM devices.
Ab initio electronic structure calculations reveal that epitaxial strain has a dramatic effect on... more Ab initio electronic structure calculations reveal that epitaxial strain has a dramatic effect on the voltagecontrolled magnetic anisotropy (VCMA) in Ta/FeCo/MgO junctions. Strain can give rise to a wide range of novel VCMA behaviors where the MA can change from a ∨to a ∧-shape electric-field dependence with giant VCMA coefficients which are asymmetric under voltage reversal. The underlying mechanism is the interplay of the strain-and electric-field-induced changes in the spin-orbit coupled d states at the interfaces and the strain-induced modification of the dielectric constant of MgO. These findings demonstrate the feasibility of highly sensitive VCMA through strain engineering, which may provide a viable avenue for tailoring magnetoelectric properties for spintronic applications.
connection with the mutual mechanisms of the Jahn−Teller orbital splitting and excess electron-in... more connection with the mutual mechanisms of the Jahn−Teller orbital splitting and excess electron-induced energy level changes in the electronic structure.
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Papers by Dorj Odkhuu