In-plane Oxygen Research Articles

Correlation between optical phonon softening and superconducting Tc in YBa2Cu3Ox within d-wave Eliashberg theory

Abstract We provide a mathematical description, based on d-wave Eliashberg theory, of the strong correlation between the experimentally observed softening of Raman modes associated with in-plane oxygen motions and the corresponding superconducting critical temperature T c , as a function of oxygen doping x, in YBa2Cu3O x . The theoretical model provides a direct link between physical trends of soft optical Ag (in-plane) oxygen modes, the level of oxygen doping x, and the superconducting T c . Different regimes observed in the trend of T c vs doping can be related to corresponding regimes of optical phonon softening in the Raman spectra. These results provide further evidence related to the physical origin of high-temperature superconductivity in rare-earth cuprate oxides and to the significant role of electron–phonon coupling therein.

Effective prediction of SnO2 conduction band edge potential: The key role of surface oxygen vacancies.

Several theoretical studies at different levels of theory have attempted to calculate the absolute position of the SnO2 conduction band, whose knowledge is key for its effective application in optoelectronic devices such us, for example, perovskite solar cells. However, the predicted band edges fall outside the experimentally measured range. In this work, we introduce a computational scheme designed to calculate the conduction band minimum values of SnO2, yielding results aligned with experiments. Our analysis points out the fundamental role of encompassing surface oxygen vacancies to properly describe the electronic profile of this material. We explore the impact of both bridge and in-plane oxygen vacancy defects on the structural and electronic properties of SnO2, explaining from an atomistic perspective the experimental observables. The results underscore the importance of simulating both types of defects to accurately predict SnO2 features and provide new fundamental insights that can guide future studies concerning design and optimization of SnO2-based materials and functional interfaces.

Pressure Driven Fractionalization of Ionic Spins Results in Cupratelike High-T_{c} Superconductivity in La_{3}Ni_{2}O_{7}.

Beyond 14GPa of pressure, bilayered La_{3}Ni_{2}O_{7} was recently found to develop strong superconductivity above the liquid nitrogen boiling temperature. An immediate essential question is the pressure-induced qualitative change of electronic structure that enables the exciting high-temperature superconductivity. We investigate this timely question via a numerical multiscale derivation of effective many-body physics. At the atomic scale, we first clarify that the system has a strong charge transfer nature with itinerant carriers residing mainly in the in-plane oxygen between spin-1 Ni^{2+} ions. We then elucidate in electron-volt scale and sub-electron-volt scale the key physical effect of the applied pressure: it induces a cupratelike electronic structure via fractionalizing the Ni ionic spin from 1 to 1/2. This suggests a high-temperature superconductivity in La_{3}Ni_{2}O_{7} with microscopic mechanism and (d-wave) symmetry similar to that in the cuprates.

High-quality graphene devoid of oxygen functionalities as conductive ink for flexible electronics and bendable all-solid-state supercapacitors

High-yielding and scalable naphthalene-assisted ball-mill exfoliation of graphite is reported here aiming at the production of high-quality graphene cost-effectively. The Raman spectral analysis indicates less-defective graphene, whereas the few-layered nature is evident from the XRD pattern and AFM images. Monolayered graphene can also be produced upon ultrasonication, which is evident from the HRTEM images and Raman spectral analysis. XPS indicated the absence of in-plane oxygen functionalities that usually disrupt the aromatic π-conjugation. Graphene is effectively utilized here to formulate a conducting ink for polyimide tape-based wires for lighting LEDs. The supercapacitor performance of the graphene as an electrode material was also assessed, where, in the three-electrode system, graphene exhibited an excellent areal capacitance of 197.22 mF/cm2 at a current density of 2 mA/cm2 and the graphene-modified carbon paste electrode retained 100 % of initial capacitance even after 7500 charge-discharge cycles. A bendable supercapacitor was also fabricated here with graphene-coated carbon cloth electrodes that exhibited a high capacitance of 524.28 mF at 0.05 mA/cm2 with the highest energy and power densities of 14.87 μWh/cm2 and 349.76 μW/cm2 respectively. The bendable device retained 99.9 % of its initial capacitance after 3000 continuous cyclic voltammetric runs. The supercapacitor delivered the same performance as the straight device during bending, twisting and even after bending at different angles.

In-plane oxygen diffusion measurements in polymer films using time-resolved imaging of programmable luminescent tags

Oxygen diffusion properties in thin polymer films are key parameters in industrial applications from food packaging, over medical encapsulation to organic semiconductor devices and have been continuously investigated in recent decades. The established methods have in common that they require complex pressure-sensitive setups or vacuum technology and usually do not come without surface effects. In contrast, this work provides a low-cost, precise and reliable method to determine the oxygen diffusion coefficient D in bulk polymer films based on tracking the phosphorescent pattern of a programmable luminescent tag over time. Our method exploits two-dimensional image analysis of oxygen-quenched organic room-temperature phosphors in a host polymer with high spatial accuracy. It avoids interface effects and accounts for the photoconsumption of oxygen. As a role model, the diffusion coefficients of polystyrene glasses with molecular weights between 13k and 350k g/mol are determined to be in the range of (0.8–1.5) × 10–7 cm2/s, which is in good agreement with previously reported values. We finally demonstrate the reduction of the oxygen diffusion coefficient in polystyrene by one quarter upon annealing above its glass transition temperature.

Computer Simulation Study of Lithium and Oxygen Adsorption on Ruthenium Dioxide (110) Surface

Metal oxides are widely considered as excellent catalysts in lithium-air batteries to promote the production of stable discharge products and achieve superior electrochemical performance. The lithium–air (Li–air) battery is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current. Despite various studies exploring the use of metal oxides as effective catalysis, the catalytic activity of ruthenium oxide (RuO2) towards lithium and oxygen ions is not fully understood. In this work, we investigate the adsorptions of lithium and oxygen on the RuO2 (110) surface using density functional theory (DFT) method. Due of the size of the supercell, and assuming that oxygen atoms occupy bulk-like positions around the surface metal atoms, only five values of (gamma) Γ are possible if constraint to a maximum of 1 monolayer (ML) of adatoms or vacancies: Γ= 0 surface is the stoichiometric surface, Γ= 1, 2 are the partially and totally oxidised surfaces, and Γ=-1, -2 are the partially and totally reduced surfaces. The addition of two oxygen atoms revealed the most stable adsorption energy is the mono-clear followed by bridging configuration. The lithium orientation between two bridging oxygen and in plane oxygen (bbi) orientation is much more stable, thus lithium generally prefers to adsorb where it will be triply coordinated to two bridging oxygen atoms and one in plane oxygen atom. Rutile RuO2 has been widely considered as an excellent catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in non-aqueous.

Size- and temperature-dependent optical, and electron field emission characteristics on SnO2 nanocrystals

Size-dependent SnO2 nanocrystals (NCs)) were synthesized using a co-precipitation technique. The particle size was varied by annealing the as-prepared SnO2 NCs with the estimated size of 2.3 nm at different temperatures. The particle size obtained was 4.7, 9.0, 15.4, 19.6, and 48.0 nm at annealing temperatures of 400, 600, 800, 1000, and 1200 °C, respectively. The XRD data revealed the tetragonal rutile structured for all SnO2 NCs. The temperature-dependent photoluminescence (PL) studies showed that the sub-bridging oxygen vacancy contributed dominantly compared to the in-plane and bridging oxygen vacancies at 5K. The function of nanocrystals’ size on field emission properties is also reported. The current density was high (1.9 μA/cm2) with modest the turn-on field (8.4 V/μm) for as-prepared SnO2 QDs with the lowest size (2.3 nm) compared to the high temperature annealed SnO2 nanocrystals.

Invigorating surface frustrated Lewis pairs on bifunctional quasi-disordered Sn-based catalyst for solar photothermocatalytic conversion of CO2 from air

Designing adsorption-enhanced solid catalysts with excellent bifunctional features is feasible for achieving carbon neutrality. In this study, surface-frustrated Lewis pair sites (sFLPs) were fabricated on a quasi-disordered Sn catalyst. Catalysts with different degrees of disorder were synthesized by thermochemical control. The disordered catalyst exhibited randomly distributed lattice disorder, in-plane oxygen vacancies, and mixed-valence Sn. The coexistence of Sn (IV, II) Lewis acidic sites and −OH Lewis basic sites was crucial in the activation of CO2. In addition, sFLPs were further stimulated on the disorder-engineered surface using simultaneous inclusion of PTA (W6+) and hydroxylation. The optimized catalyst exhibited an exceptionally high adsorption capacity and photothermocatalytic activity for 400 ppm CO2 in air compared to pristine SnO2. The enhanced adsorption and photothermocatalytic activity were attributed to distinctive chemistry of the redox-active sFLPs. This study highlights the potential of high-density sFLPs on disordered catalysts for CO2 abatement from the air.

Defect-Rich SnO2 Nanofiber as an Oxygen-Defect-Driven Photoenergy Shield against UV Light Cell Damage.

Usually, most studies focus on toxic gas and photosensors by using electrospinning and metal oxide polycrystalline SnO2 nanofibers (PNFs), while fewer studies discuss cell-material interactions and photoelectric effect. In this work, the controllable surface morphology and oxygen defect (VO) structure properties were provided to show the opportunity of metal oxide PNFs to convert photoenergy into bio-energy for bio-material applications. Using the photobiomodulation effect of defect-rich polycrystalline SnO2 nanofibers (PNFs) is the main idea to modulate the cell-material interactions, such as adhesion, growth direction, and reactive oxygen species (ROS) density. The VO structures, including out-of-plane oxygen defects (op-VO), bridge oxygen defects (b-VO), and in-plane oxygen defects (ip-VO), were studied using synchrotron analysis to investigate the electron transfer between the VO structures and conduction bands. These intragrain VO structures can be treated as generation-recombination centers, which can convert various photoenergies (365-520 nm) into different current levels that form distinct surface potential levels; this is referred to as the photoelectric effect. PNF conductivity was enhanced 53.6-fold by enlarging the grain size (410 nm2) by increasing the annealing temperature, which can improve the photoelectric effect. In vitro removal of reactive oxygen species (ROS) can be achieved by using the photoelectric effect of PNFs. Also, the viability and shape of human bone marrow mesenchymal stem cells (hMSCs-BM) were also influenced significantly by the photobiomodulation effect. The cell damage and survival rate can be prevented and enhanced by using PNFs; metal oxide nanofibers are no longer only environmental sensors but can also be a bio-material to convert the photoenergy into bio-energy for biomedical science applications.

An effective strategy to improve the photothermocatalytic activity of Co3O4 for VOCs degradation: Specifically enhancing the surface lattice oxygen activity

Co3O4 catalysts with active surface lattice oxygen were constructed via a simple solvothermal method by adopting isopropyl alcohol (IPA) or tert-butyl alcohol (TBA) as solvent. The obtained Co3O4-IPA and Co3O4-TBA exhibit flower-like structures with (112) planes exposed on the surface. Due to abundant unsaturated Co3+ sites existing on the (112) plane, the content and activity of surface lattice oxygen on Co3O4-IPA and Co3O4-TBA are much higher than that on Co3O4-MA and Co3O4-EA, which prepared with methyl alcohol or ethyl alcohol as a solvent. The robust surface lattice oxygen on Co3O4-IPA and Co3O4-TBA facilitates the ring-opening process during photothermocatalytic oxidation of toluene, significantly promoting the catalytic performance. In the static atmosphere, about 98% of toluene conversion and 80% of CO2 yield can be achieved on Co3O4-IPA and Co3O4-TBA under full-spectrum light irradiation of 325 mW/cm2, much higher than 89% and 73% of conversion, 50% and 26% of CO2 yield on Co3O4-EA and Co3O4-MA, respectively.

Effect of operating conditions and micro-porous layer on the water transport and accumulation in proton exchange membrane fuel cells

Accurate measurement of water transport in an operating proton exchange membrane fuel cell (PEMFC) and water accumulation in the electrodes is crucial for understanding the impact of operating conditions and transport layer configurations on cell performance. A water balance setup, based on in-line gas flowmeter, pressure, relative humidity and temperature sensors, was developed and demonstrated to track the real-time water transport and accumulation within operating PEMFCs. Current results indicate that changing operating conditions have a dramatic effect on the water transport across the membrane, while the ratio of water transported to produced remains relatively constant with current density. Under dry conditions, water moves from anode to cathode while increasing humidity and decreasing temperature enhance cathode to anode water movement. Adding a micro-porous layer (MPL) to the cathode gas diffusion layer (GDL) increases the water back-diffusion from the cathode to the anode at all operating conditions, but the increase is not very significant and only results in a prominent performance increase at 60 °C and 70% RH. The improved performance at 60 °C and 70% RH is likely due to: (a) increased water vaporization, since less water accumulation was measured in the electrode; and (b) creation of in-plane oxygen pathways in the MPL around localized liquid water blockages in the GDL. Based on these results, the use of different operating conditions might have been the key contributing factor for the different behavior observed when an MPL was introduced in previous literature.

Investigation of Hydrated Dy(III) and MgSO4 Leaching Agent Ion Adsorption on (001) Surface of Montmorillonite: A Study Using Density Functional Theory

Kaolinite is one of the principal rare earth element (REE) ion-adsorption clays that hosts a wide range of elements, including Dy(III) as a representative example. Ammonium sulfate is a typical salt used to leach REEs. Due to the carbon dioxide emissions which occur during ammonia production, it is urgently necessary to develop low environmental pollution leaching agents that can replace (NH4)2SO4. MgSO4 is regarded as the most promising eco-friendly leaching agent. Herein, the first-principles plane-wave pseudopotential method based on the density functional theory (DFT) was used to investigate the stable adsorption structures of Dy(III) and its hydrated ions, MgSO4 leaching agent ions and the corresponding hydrated ions on the surface of kaolinite, which revealed the adsorption mechanism of Dy(III), Mg(II), and SO42− on the silico–oxygen plane and the aluminum–hydroxyl plane of kaolinite. Based on the research results of the steric hindrance effect of Dy(III) on the silico–oxygen plane and the aluminum–hydroxyl plane of kaolinite, the adsorption of Dy(H2O)103+ was more stable on the silico–oxygen plane. It was easier to leach out Dy(III) with MgSO4, while SO42− tended to interact with the rare earth ions in an aqueous solution. The results provide theoretical guidance for efficient rare earth extraction and obtaining novel efficient leaching agents.

Measuring the through-plane and in-plane oxygen apparent diffusion coefficients in the gas diffusion layer

Accurately predicting oxygen mass transport resistance and current distribution in fuel cells requires significant knowledge of oxygen diffusion coefficients in both in-plane and through-plane directions. However, there are few methods for measuring in-plane oxygen diffusion coefficients, which are important parameters for simulating oxygen flux distribution in gas diffusion layers (GDLs). In this study, we establish measurement methods and calculations for both in-plane and through-plane oxygen diffusion coefficients. Using in-house designed cells, we measure the in-plane and through-plane oxygen apparent diffusion coefficients of a commercial carbon paper (AvCarb EP40) at various torques and gas flow rates. We also simulate oxygen flux distributions in the GDL under each torque and gas flow rate. Our results show that the channel part is the major contributor to total oxygen flux at high torque conditions and that an increase in torque leads to a decrease in the contribution from the land part. Simulation results also suggest that a higher gas flow rate and lower torque contribute to a more uniform distribution of oxygen flux in the GDL.

Looking Outside the Square: The Growth, Structure, and Resilient Two-Dimensional Surface Electron Gas of Square SnO2 Nanotubes.

Nanotechnology has delivered an amazing range of new materials such as nanowires, tubes, ribbons, belts, cages, flowers, and sheets. However, these are usually circular, cylindrical, or hexagonal in nature, while nanostructures with square geometries are comparatively rare. Here, a highly scalable method is reported for producing vertically aligned Sb-doped SnO2 nanotubes with perfectly-square geometries on Au nanoparticle covered m-plane sapphire using mist chemical vapor deposition. Their inclination can be varied using r- and a-plane sapphire, while unaligned square nanotubes of the same high structural quality can be grown on silicon and quartz. X-ray diffraction measurements and transmission electron microscopy show that they adopt the rutile structure growing in the [001] direction with (110) sidewalls, while synchrotron X-ray photoelectron spectroscopy reveals the presence of an unusually strong and thermally resilient 2D surface electron gas. This is created by donor-like states produced by the hydroxylation of the surface and is sustained at temperatures above 400°C by the formation of in-plane oxygen vacancies. This persistent high surface electron density is expected to prove useful in gas sensing and catalytic applications of these remarkable structures. To illustrate their device potential, square SnO2 nanotube Schottky diodes and field effect transistors with excellent performance characteristics are fabricated.

Revealing the Anisotropy in Protonation-Induced Electronic Phase Transitions of Rare-Earth Nickelates within a Marine Environment

Although the discovery of the electrochemical protonation-induced electronic phase transition of rare-earth nickelates (ReNiO3) enables potential application in sensing the ocean electric field that simulates the working principle of the ampullary organ of marine animals, whether such a functionality is anisotropic is previously overlooked. Herein, we demonstrate the anisotropy in the protonation-induced electronic phase transition in ReNiO3 (Re = Sm, Nd, and Eu) thin films as electrochemically triggered in an ocean environment. A larger elevation in the material resistivity triggered by an electric field within an ocean environment is observed for ReNiO3/LaAlO3(110), compared to ReNiO3/LaAlO3(001) and ReNiO3/LaAlO3(111). This is attributed to the orientation-related in-plane oxygen atomic density that results in more effective in-plane proton diffusion along the adjacent oxygen position, as further confirmed by the electrochemical cyclic voltammetry characterization. In addition, the larger activation energy associated to the anisotropic in-plane electronic structures of ReNiO3/LaAlO3(110) is also expected to promote the formation of electron-localized orbital configurations upon hydrogenation. As demonstrated, anisotropy sheds light on another possibility that can be further introduced to regulate the protonation-induced electronic phase transition properties of ReNiO3 for its potential applications such as ocean electric field sensing or biosensing.

Observation of Anomalously Large Magnetoelectric Coupling in the Hexagonal Z‐Type Ferrite Films

AbstractAlthough the bulk hexaferrites are known to exhibit strong magnetoelectric (ME) effects near room temperature, the same effects are not realized in a thin film form. Herein, the growth of nearly epitaxial Co2Z‐type hexaferrite Ba0.3Sr2.7Co2Fe24O41 (BSCFO) thin films on a SrTiO3 (111) substrate by a chemical solution deposition method is reported. The reciprocal space mapping on the annealed BSCFO films reveals broadening along the qx directions in the (0014) and (0018) peaks, indicating that the oxygen planes belonging to the off‐centered octahedra have randomly distributed out‐of‐plane tilt to indicate significant disorder in the crystallographic orientation. Quantitative investigations reveal that both ME susceptibility and modulated electric polarization (ΔP) by magnetic field up to 370 K in the BSCFO films are always larger than those of the Co2Z‐type single crystal by ≈2–15 times and further increase upon having enhanced qx broadening in the (0014) and (0018) peaks. As the off‐centered octahedral sites can be a primary source of ΔP as predicted by the p–d hybridization mechanism, these results indicate that effective off‐centering could be further enhanced by the orientational disorder. This study identifies the potential of applying the ME hexaferrite films for multifunctional devices.

Cavity magnon-polaritons in cuprate parent compounds

Cavity control of quantum matter may offer new ways to study and manipulate many-body systems. A particularly appealing idea is to use cavities to enhance superconductivity, especially in unconventional or high-$T_c$ systems. Motivated by this, we propose a scheme for coupling Terahertz resonators to the antiferromagnetic fluctuations in a cuprate parent compound, which are believed to provide the glue for Cooper pairs in the superconducting phase. First, we derive the interaction between magnon excitations of the Ne\'el-order and polar phonons associated with the planar oxygens. This mode also couples to the cavity electric field, and in the presence of spin-orbit interactions mediates a linear coupling between the cavity and magnons, forming hybridized magnon-polaritons. This hybridization vanishes linearly with photon momentum, implying the need for near-field optical methods, which we analyze within a simple model. We then derive a higher-order coupling between the cavity and magnons which is only present in bilayer systems, but does not rely on spin-orbit coupling. This interaction is found to be large, but only couples to the bimagnon operator. As a result we find a strong, but heavily damped, bimagnon-cavity interaction which produces highly asymmetric cavity line-shapes in the strong-coupling regime. To conclude, we outline several interesting extensions of our theory, including applications to carrier-doped cuprates and other strongly-correlated systems with Terahertz-scale magnetic excitations.

Cover Feature: High Visible Light Photocatalytic Activity of SnO2‐x Nanocrystals with Rich Oxygen Vacancy (Eur. J. Inorg. Chem. 42/2021)

The Cover Feature shows a tin oxide photocatalyst with strong visible light catalytic performance. By controlling the ratio of Sn4+ to Sn2+, SnO2−x nanocrystals with controllable oxygen vacancies were synthesized. Due to the presence of in-plane oxygen defects, the valence band moves up and the band gap can be narrowed, which result in the high visible light harvesting and the excellent photocatalytic activity. The result indicates that the photocatalytic performance of SnO2−x nanocrystals can be tuned by controlling the oxygen vacancy. More information can be found in the Full Paper by H. Zhan and co-workers.

Graphene Quantum Dots Improved "Caterpillar"-like TiO2 for Highly Efficient Photocatalytic Hydrogen Production.

Photocatalytic water splitting for hydrogen production via heterojunction provides a convenient approach to solve the world crises of energy supply. Herein, graphene quantum dots modified TiO2 hybrids (TiO2-GQDs) with a “caterpillar”-like structure exhibit stronger light absorption in the visible region and an enhanced hydrogen production capacity of about 3.5-fold compared to the pristine TiO2 caterpillar. These results inferred that the addition of GQDs drastically promotes the interfacial electron transfer from GQDs to TiO2 through C–O–Ti bonds via the bonding between oxygen vacancy sites in TiO2 and in-plane oxygen functional groups in GQDs. Using a “caterpillar”-like structure are expected to provide a new platform for the development of highly efficient solar-driven water splitting systems based on nanocomposite photocatalyst.

Role of surface diffusion in formation of unique reactivity for graphite oxidation: Time-resolved measurements in a pulsed diffusion reactor

Quantification of oxidation kinetics is essential to develop graphitic materials for diverse applications: from refractories found in gas-cooled nuclear reactors to catalysts needed for chemical manufacturing. Using well-defined highly oriented pyrolytic graphite, low-pressure isotopic transient experiments combined with controlled annealing periods are used to resolve the role of surface diffusion and quantify oxidation kinetics with nanomole-precision. We observe an unexpected increase in reactivity following annealing which is explained by the role of surface diffusion increasing the probability for trapping mobile oxygen at more reactive edge sites. Here, the locus of adsorption and spillover to the basal plane is distinct from the trapping location creating a more active oxygen species. Isotopic products reflect the population dynamics of oxygen added at the edge and surface diffusion that relocates basal plane oxygen to more reactive edge sites. Since this process proceeds in parallel with direct oxidation reactions, it is not likely to be observed using steady-state or conventional ‘bulk’ characterization techniques. Our unique time-resolved non-equilibrium measurement in a well-defined transport regime, enables observation of three distinct behaviors: short-term deactivation due to the balance of rates in oxygen supply/product formation, reactivity increases due to surface diffusion and longer-term reactivity increase with oxygen accumulation.