Octahedral Sites Research Articles

Microbial-induced structural changes in non-stoichiometric magnetite via radioanalytical methods

AbstractStructural alterations in non-stoichiometric magnetite induced by microorganisms are studied by nuclear methods. Magnetite samples were exposed to fungal strain known for its immobilization capabilities. Neutron activation analysis identified iron as the dominant element. The presence of maghemite in non-stoichiometric magnetite complicates the determination of iron sites by Mössbauer spectrometry. Mössbauer spectra recorded at 4.2 K display overlapping lines corresponding to tetrahedral and octahedral iron sites. Application of external magnetic field of 6 T improved the spectral resolution and revealed a presence of distinct sextets. Interaction with Aspergillus niger did not notably affect magnetite´s magnetic properties, indicating its stability.

Isotope-dependent site occupation of hydrogen in epitaxial titanium hydride nanofilms.

Hydrogen, the smallest and lightest element, readily permeates a variety of materials and modulates their physical properties. Identification of the hydrogen lattice location and its amount in crystals is key to understanding and controlling the hydrogen-induced properties. Combining nuclear reaction analysis (NRA) with the ion channeling technique, we experimentally determined the locations of H and D in epitaxial nanofilms of titanium hydrides from the analysis of the two-dimensional angular mappings of NRA yields. Here we show that 11 at% of H are located at the octahedral site with the remaining H atoms in the tetrahedral site. Density functional theory calculations revealed that the structures with the partial octahedral site occupation are stabilized by the Fermi level shift and Jahn-Teller effect induced by hydrogen. In contrast, D was found to solely occupy the tetrahedral site owing to the mass effect on the zero-point vibrational energy. These findings suggest that site occupation of hydrogen can be controlled by changing the isotope mixture ratio, which leads to promising manifestation of novel hydrogen-related phenomena.

Modulating Coordination Environment of Cobalt-Based Spinel Octahedral Metal Sites to Boost Metal–Oxygen Bond Covalency for Reversible Lithium–Oxygen Batteries

Modulating Coordination Environment of Cobalt-Based Spinel Octahedral Metal Sites to Boost Metal–Oxygen Bond Covalency for Reversible Lithium–Oxygen Batteries

Low‐Coordination Crystallographic Lattice Engineering to Discover Ce3+‐Activated Ultra‐Wide Visible‐to‐Near‐Infrared Luminescent Materials

AbstractDevelopment of ultra‐broadband visible‐to‐near‐infrared (VIS‐NIR) luminescent materials is a challenging but rewarding endeavor, as they are highly desirable for a number of applications in photonics, optoelectronics, and biological sciences. Nevertheless, to date, rare earth‐doped phosphors that can be efficiently excited by blue light and produce broadband emission in the VIS‐NIR regions remain scarce. In this study, a series of Ce3+‐doped Ba3M4O9 (M = Sc, Lu, Y) broadband luminescent materials are designed based on low‐coordination crystallographic lattice engineering. Among these materials, Ba3Y4O9:Ce3+ produces a continuous ultra‐wide VIS‐NIR emission (λem = 660 nm) in the range of 500–950 nm under 410 nm light excitation. This emission wavelength is the longest among those observed in Ce3⁺‐doped oxide materials. Structural refinement, theoretical calculation, and spectral analysis demonstrate that this VIS‐NIR broadband emission is attributed to the occupying multiple distorted octahedral lattice sites by Ce3+ in Ba3Y4O9. Several strategies are employed to enhance the luminescence intensity and thermal stability of this material, including the use of carbon paper coating, the incorporation of co‐solvents, and the addition of GeO₂ or ZrO₂. Furthermore, the as‐prepared materials demonstrate multifunctional applications in white light‐emitting diodes (WLED), night vision, and fluorescent thermometers. This study offers insights into the design of Ce3+‐doped ultra‐wide VIS‐NIR light‐emitting materials.

Role of divalent doping at A-sites (A=Ca2+, Sr2+, Ba2+ & Pb2+) on thermoelectric and magnetoresistive properties in La0.67(Bi0.0835Na0.0835) A0.165MnO3

The present work reports on the effect of divalent ion doping (Ca2+, Sr2+, Pb2+ & Ba2+) ions at A-site in the compound with compositional formula La0.67(Bi0.0835Na0.0835)A0.165MnO3 on structural, magnetic, magneto-transport and thermoelectric properties. X-ray diffraction reveals orthorhombic structure for calcium and barium doped with no peak splitting observed at ~ 32o whereas rhombohedral structure for strontium and lead dopants with a peak splitting in the main intensity. Doping with divalent ions at A-site in La0.67(Bi0.0835Na0.0835)A0.165MnO3 manganites has introduced Mn2+ ions, changing the ratio of Mn3+/Mn4+ in octahedral site and this has been confirmed from X-ray photospectroscopy studies. The field emission scanning electron microscope images confirm different grain sizes and morphologies for different doping elements and distinguished variation is noticed for strontium doped manganites with a grain size of 1.08µm. Room temperature ferromagnetic behavior was observed in the samples at room temperature except for calcium doped sample and magnetic behavior has been discussed on the basis of the various interactions between mixed valence manganese ions and Mn3+/Mn4+ ratio. Electrical resistivity (ρ) as a function of temperature (T) without magnetic field indicates the double peak behavior and with the application of external magnetic fields, the double peak disappears, in all the investigated samples. Highest MR% at their respective transition temperatures (TP1) has been obtained for lead doped samples when compared to barium, strontium and calcium samples. Activation energies (EP) estimated decreases initially for calcium and strontium whereas it increases for lead and barium dopants i.e. for further increases in ionic radii. The change of sign from positive to negative in Seebeck coefficient (S) was noticed with increasing ionic radii suggesting the variation in the nature of charge carriers. The electron-electron, electron-magnon, magnon-magnon scattering mechanism contributes to the temperature dependent resistivity and thermopower in the low temperature region while in the paramagnetic insulating region is governed by a small polaron hopping mechanism.

Cr3+-doped Na2CaSn2Ge3O12 garnet showing broadband near-infrared emission at 820 nm with zero thermal quenching and near-unity quantum yield

The continually advancing near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) hold pivotal significance in optical imaging and NIR spectroscopy. Cr3+-doped garnet broadband NIR phosphors have attracted considerable attention owing to their high optical performance enabled by the rigid structure. Nonetheless, the emission wavelength is severely restricted, and longer wavelength emissions usually result in inferior quantum efficiency and poor luminescence stability. In this work, the concurrent reconstruction of dodecahedral and octahedral sites by introducing [Na+-Sn4+]C unit in the framework of Na2CaSn2Ge3O12 garnet contributes to the Cr3+ broadband NIR emission spanning 700–1200 nm, with a peak at 820 nm. Utilizing a charge compensation strategy via Ta5+ codoping largely boosts the internal quantum efficiency (IQE) of Na2CaSn2Ge3O12:Cr3+ from 93.06 % up to 95.04 %. Trap-mediated energy compensation is proposed to achieve a record-breaking zero-thermal-quenching behavior (99.39 %@423 K) of Cr3+-doped garnet with such a longer wavelength emission. The encapsulated prototype broadband NIR pc–LED gives rise to an overwhelming NIR output power of 590.9 mW@1300 mA and a photoconversion efficiency (PCE) of 32.62 % at 30 mA, rendering exceptional performance in night vision, detection, and NIR imaging applications.

Multiplet XPS analysis of the Mn 2p for Mn3O4 thin films

In this work, we performed a detailed analysis of the x-ray photoemission spectroscopy (XPS) of the Mn 2ppeak for Mn3O4(001) thin films. This is a challenging task since Mn3O4is composed of two different cations, Mn2+at tetrahedral and Mn3+at octahedral sites, which both contribute to the XPS spectra. The oxide spectra consist of many multiplets arising from the angular momentum coupling of the open Mn 2pand 3dshells, thus increasing the spectrums' complexity. Moreover, the energy spacing and intensities of the different multiplets also reflect the covalent mixing between Mn 3dand O 2pshells. However, we show that a detailed analysis, which provides relevant information about the cations in the oxide structure, is possible. We prepared experimentally different Mn3O4films on Au(111), and their structure was monitored with the diffraction pattern obtained with low-energy electron diffraction. The Mn 2pspectra were fit, guided by cluster model theoretical predictions, and checked for films prepared at different oxygen partial pressures. Therefore, we could observe the Mn2+and Mn3+cations' relative concentration in the Mn 2pmains peaks.

DFT and AIMD studies of SnFe2O4 as a promising anode for Li-ion batteries

Tin ferrite (SnFe2O4) is considered as a perspective lithium ion battery anode, owing to its low cost, large theoretical capacity, low toxicity, structural stability, and easy synthesis method. Prior research has been done on the performance of lithium storage in SnFe2O4. However, the electrochemical processes that take place during the lithiation-delithiation cycle of LIBs have not been explained in depth yet. In order to understand the discharge mechanism in the LixSnFe2O4 anode (x = 0 to 2), we systematically investigated its electrochemical characteristics, structural and electronic properties, average formation energies, open-circuit voltages, diffusion coefficient, and volume expansion using density functional theory. According to our calculations, an increase in Li concentration x up to 1.125 leads to enhanced stability of the LixSnFe2O4 systems. During this process, Li+ ions prefer to be intercalated at the octahedral 16c sites, inducing the displacement of Sn2+ ions from tetrahedral sites 8a to 16c and 48f sites. However, for 1.125 < x < 2, lithium ions tend to occupy the less stable sites 48f , which reduces the stability of LixSnFe2O4 systems.Additionally, the calculated lithium intercalation voltage for full lithiation Li1.125SnFe2O4 is equal to 1.5 V, and the distortion of the LixSnFe2O4 system occurs at a voltage of 0.75 V, which is in well agreement with experimental results. The Li-coefficient diffusion on SnFe2O4 at 300 K is calculated by ab initio molecular dynamic simulation and equal to 8.22 × 10−8 cm2/s, which indicates the excellent mobility of Li ions in SnFe2O4. Considering all these results, we can suggest SnFe2O4 as a promising negative electrode material for lithium-ion batteries.

Effect of Cr substitution in ZnFe2O4 nanoparticles on the electron transfer at electrochemical interfaces

In this study, we explored the effect of Cr³⁺ substitution by partially and fully replacing Fe³⁺ in the normal spinel ZnFe₂O₄ crystal structure at electrochemical interfaces. The resulting ZnCrₓFe₂₋ₓO₄ nanomaterials exhibited an average particle size between 20 and 50 nm with a spherical morphology. The materials also demonstrated energy band gaps ranging from 2.1 to 3.1 eV. X-ray diffraction (XRD) analysis confirmed that all the synthesized materials maintained a normal spinel structure, attributed to the octahedral site preference energy (OSPE) of Zn²⁺, Fe³⁺, and Cr³⁺ ions. Electrochemical performance assessments revealed that the ZnFe₂O₄-based sensor achieved a sensitivity of (37.8 ± 0.2) μA/mM with a kinetic rate constant of (13.1 ± 2.8) ms⁻¹, while the ZnCr₂O₄-based sensor exhibited a sensitivity of (32.4 ± 0.5) μA/mM and a kinetic rate constant of (3.73 ± 0.55) ms⁻¹ in the detection of paracetamol, whereas ZnCrFeO4 sensor has produced the second-best sensitivity (35.7 ± 0.1 μA/mM) and the rate constant (4.53 ± 0.54 ms⁻¹) with the lowest limit of detection (1.94 ± 0.01 μM). These differences in electrochemical performance were correlated with the variations in the energy band gaps caused by the restructuring of the normal spinel structure. Our findings indicate that the ZnFe₂O₄ sensor has a higher potential for direct electron transfer, whereas the other sensors are more likely to facilitate surface-mediated electron transfer.

Modulating charge transfer and constructing synergistic bimetallic active sites for CO-SCR reactions in inverse spinel

The selective catalytic reduction of NO by CO (CO-SCR) are frequently catalyzed by spinel due to its exceptional stability and redox capabilities. In this research, a ternary metal-based inverse spinel catalyst Cu0.67Mn0.33Fe2O4 was synthesized utilizing the glycerol self-templating technique. Some Fe3+ (Fe3+Td) sites are transferred to vacant octahedral sites through the occupancy of tetrahedral sites by Mn species. Mn3+ (Mn3+Td) sites synergistically interact with Cu2+ and Fe3+ ions on the octahedral sites to promote charge transfer, producing numerous oxygen-defective and highly mobile oxygen species and constructing Cu+-Ov-Fe2+ active sites on the surface. Various characterizations demonstrated that Cu+-Ov-Fe2+ has greater catalytic activity, resistance to alkali metals, and water toxicity than the Cu2+-Ov-Fe2+ active site of CuFe2O4. In situ DRIFTS further revealed the reaction mechanism of the ternary metal-based inverse spinel catalyst, and this study provides novel perspectives on the development of Cu-based catalysts for CO-SCR.

Elucidating the effect of annealing temperature on the atomic-level surface structure evolution and electrochemical performance of Mo doped LiMn2O4 cathode materials

Critical barriers to the extensive applications of the spinel LiMn2O4 cathodes include grievous capacity degradation and structural collapse. Bulk elemental doping combining surface modification, which is a common approach to address these challenges. Here, synchronous bulk Mo-doped and in-situ surface reconstructed layer coated LiMo0.02Mn1.98O4 cathodes are prepared by tuning the annealing temperatures. Using the spherical aberration-corrected scanning transmission microscopy (Cs-STEM) technique, we demonstrate that part of Mo6+ ions dopes into the octahedral Mn 16d sites to form LiMo0.02Mn1.98O4 that strengthens bulk structural stability. The other part of Mo6+ ions or the Mn atom occupying the Mn 16c sites of the spinel to form a surface reconstructed layer on the outermost surface that suppresses the side reaction and slows down the decomposition of the electrolyte. Specifically, the LiMo0.02Mn1.98O4 cathode calcined at 750 °C with an appropriate surface reconstructed layer exhibits an outstanding capacity retention of 76.28 % after 1000 cycles at 10C at 25 °C. Our work provides a simple and novel way toward high electrochemical performance tuning for spinel LiMn2O4 cathodes.

Enhancement of sodium ion conductivity in phosphate-based glass-ceramics by chemical substitution approach

A NASICON-type sodium-ion conducting material was synthesized via the glass-ceramic route by investigating the zinc doped Na2O–Al2O3–TiO2–P2O5 system. The glasses and glass-ceramics corresponding to the formula Na2+xAl1-xZnxTi(PO4)3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1), labeled as (NAZTP-Gx) and (NAZTP-GCx) respectively, were characterized using different techniques. Differential Scanning Calorimetry (DSC) measurements were carried out to identify the characteristic temperatures, the glass transition (Tg) and the crystallization temperature (Tc). X-ray Diffraction (XRD) analysis of the glass-ceramics confirmed the formation of a solid solution Na2+xAl1-xZnxTi(PO4)3 NASICON phase, Theoretical calculations employing the Perdew–Burke–Ernzerhoff generalized gradients approximation (PBE-GGA) model supported the potential substitution of aluminum by zinc in the octahedral site in the NASICON-phase. Further structural insights were obtained through Infrared (IR) and Raman spectroscopies. Scanning electron microscopy (SEM) analysis revealed a distinct flower-like shape of the formed crystallites in the glass-ceramic NAZTP-GC0.2. Electrical characterization using electrochemical impedance spectroscopy (EIS) demonstrated that the NAZTP-GC0.2 sample exhibited the highest ionic conductivity at 300 °C, reaching 4.1 × 10−5 (Ω−1 cm−1) with an activation energy of 0.25 eV. The DC polarization was performed on the NAZTP-GC0.2 glass-ceramic, revealing that the ions are the main charge carriers in the sample. This comprehensive analysis provides valuable insights into the partial zinc doping of NASICON glass-ceramics, offering potential for improved performance as solid electrolytes in various applications.

Understanding Trace Iron and Chromium Incorporation During Gibbsite Crystallization and Effects on Mineral Dissolution.

Incorporation of pollutants, e.g., heavy metals, or critical elements, e.g., lithium, as impurities in mineral phases can significantly affect their mobility or sequestration in the environment. Even when present at low concentrations, impurities can alter the solubility and reactivity of the host mineral. In this study, we investigate the incorporation of trace amounts of iron (Fe3+) and chromium (Cr3+) during the crystal growth of the aluminum (Al3+) hydroxide, gibbsite, a major component of bauxite ores, an important soil mineral, and a dominant mineral phase in stored radioactive wastes. Using a comprehensive suite of analytical techniques, we show that both Cr3+ and Fe3+ can be incorporated into the gibbsite lattice during coprecipitation by replacing Al3+ in octahedral sites. These small amounts are consistent with limited to no structural isomorphism shared between Al3+ and Cr3+/Fe3+ hydroxide precipitates, nor room temperature miscibility of their isostructural M2O3 oxide forms, in contrast with oxyhydroxide forms where Al3+ and Fe3+ share similar structural topologies. Despite the limited uptake of Cr3+/Fe3+, we show that these impurities have significant implications for gibbsite dissolution behavior. The limited uptake of Cr3+/Fe3+ (e.g. 0.43% Cr3+ and 0.4% Fe3+), we show that these impurities have significant implications for gibbsite dissolution behavior and subsequent reactivity in complex environments.

Nanostructured spinel ferrites: A comprehensive study on the synthesis, characterization, and magnetic properties of Zn and Mn substituted magnetite nanoparticles produced through the co-precipitation method

Seven cubic spinel ferrite nanoparticles were successfully synthesized through the co-precipitation method. These nanoparticles include Fe3O4, Zn0.4Fe0.62+Fe23+O4, Mn0.4Fe0.62+Fe23+O4, Zn0.6Mn0.4Fe0.42+Fe1.63+O4, Zn0.4Mn0.6Fe0.42+Fe1.63+O4, Zn0.4Mn0.4Fe0.22+Fe23+O4, and Zn0.4Mn0.4Fe0.42+Fe1.83+O4. The Rietveld method was used to analyze X-ray diffraction data, confirming that all samples have a single-phase cubic spinel structure. The presence of zinc and manganese ions in magnetite lattice leads to changes in lattice parameters and crystallite size, resulting in a range of 7–12 nm crystallite sizes. Fourier transform infrared spectroscopy (FT-IR) analysis of nanoparticles reveals two significant adsorption peaks at 560-576 cm−1 and 437-449 cm−1, corresponding to metal ion stretching vibrations at tetrahedral and octahedral sites. The X-ray photoelectron spectroscopy (XPS) analysis revealed the presence of iron, zinc, and manganese in various oxidation states. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) images showed spherical, agglomerated nanoparticles. The study confirmed the elemental composition and mapping images of prepared samples using energy-dispersive X-ray spectroscopy (EDS). The magnetic properties of the synthesized nanoparticles were meticulously examined utilizing a vibrating sample magnetometer (VSM) at room temperature. A direct correlation is established between the structural alterations induced by Zn2+/Mn2+ and their subsequent effects on magnetic characteristics, specifically through the reallocation of cations and the mechanisms of electron hopping occurring at the B-sites. The structural modifications result in enhanced superparamagnetic behavior, exhibiting saturation magnetization values between 46.01 and 69.38 emu/g. The sustainable characteristics of these materials render them highly viable options for applications in environmental remediation and green technology.

Effect of iron doping on nickel aluminate photocatalytic activity towards the degradation of methylene blue under visible and UV light

The major issue that industries have is the degradation of organic dye in wastewater. In this study, we introduce an iron-doped spinel-type photocatalyst for dye degradation. Due to advantages like a lower band gap, and favorable magnetic characteristics, iron-doped nickel aluminate can be a viable catalyst for dye degradation. Nickel aluminate and iron-doped Nickel aluminate NiAl2-xFexO4 (x = 0.05, 0.1, 0.5, and 1.0) were synthesized by the sol-gel method using citric acid as a capping agent. The obtained samples were calcined at 800 °C for 4 h. The spinel was characterized using X-ray diffraction (XRD) which helped in the identification of the purity of the phase and the calculation of the average crystallite size. Fourier Transform Infrared (FT-IR) spectra confirmed the presence of iron in the octahedral site; (SEM-EDAX) Scanning Electron Microscopy facilitated the surface morphology and Energy-Dispersive X-ray analysis provided the elemental confirmation and UV-DRS techniques assisted in the calculation of the band gap using the Tauc plot method. Photocatalytic efficiency was investigated against the cationic dye Methylene blue under UV and Visible light. The results showed degradation of 94.25% under UV light and 83.51% under visible light in 90 min and 150 min respectively using iron-doped nickel aluminate.

Chromium Immobilization as Cr-Spinel by Regulation of Fe(II) and Fe(III) Concentrations

The complex environmental conditions at Cr-contaminated sites, characterized by uneven ion distribution, oxidants competition, and limited solid-phase mobility, lead to inadequate mixing of Fe-based reducing agents with Cr, posing significant challenges to the effectiveness of Cr remediation through Cr-spinel precipitation. This study investigates the distinct roles of Fe(II), Fe(III), and Cr(III) in Cr-spinel crystallization under ambient temperature and pressure. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray absorption near-edge structure spectroscopy, and Mössbauer spectroscopy were employed to elucidate the phase composition, microstructure, and ion coordination within the precipitates. Our findings indicate that Fe(II) acts as a catalyst in the formation of the spinel phase, occupying octahedral sites within the spinel structure. Under the catalytic influence of Fe(II), Fe(III) transitions into the spinel phase, occupying both the tetrahedral and the remaining octahedral sites. Meanwhile, Cr(III), due to its high octahedral site preference energy, preferentially occupies the octahedral sites. When Fe(II) or Fe(III) is present but does not meet the ideal stoichiometric ratio, a deficiency in Fe(II) leads to low yield and poor crystallinity of Cr-spinel, whereas a deficiency in Fe(III) can completely inhibit its formation. Conversely, when either Fe(II) or Fe(III) is in excess, the formation of Cr-spinel remains feasible. Furthermore, metastable Cr phases can be transformed into stable Cr-spinel by adjusting the Fe(II)/Fe(III)/Cr(III) ratio. These results highlight the broad range of conditions under which Cr-spinel mineralization can occur in environmental settings, enhancing our understanding of the mechanisms driving Cr-spinel formation in Cr-contaminated sites treated with Fe-based reducing agents. This research provides critical insights for optimizing Cr remediation strategies.

Importing Atomic Rare‐Earth Sites to Activate Lattice Oxygen of Spinel Oxides for Electrocatalytic Oxygen Evolution

Spinel oxides have emerged as highly active catalysts for the oxygen evolution reaction (OER). However, due to covalency competition, the OER process on spinel oxides often follows an arduous adsorbate evolution mechanism (AEM) pathway. Herein, we propose a novel rare‐earth sites substitution strategy to tune the lattice oxygen redox of spinel oxides and bypass the AEM scaling relationship limitation. Taking NiCo2O4 as a model, the incorporation of Ce into the octahedral site induces the formation of Ce‐O‐M (M: Ni, Co) bridge, which triggers charge redistribution in NiCo2O4. The developed Ce‐NiCo2O4 exhibits remarkable OER activity with a low overpotential, satisfactory electrochemical stability, and good practicability in anion‐exchange membrane water electrolyzer. Theoretical analyses reveal that OER on Ce‐NiCo2O4 surface follows a more favorable lattice oxygen mechanism (LOM) pathway and non‐concerted proton‐electron transfers compared to pure NiCo2O4, as further verified by pH‐dependent behavior and in situ Raman analysis. 18O‐labeled electrochemical mass spectrometry directly demonstrates that oxygen originates from the lattice oxygen of Ce‐NiCo2O4 during OER. It is discovered that electron delocalization of Ce 4f states triggers charge redistribution in NiCo2O4 through the Ce‐O‐M bridge, favoring antibonding state occupation of Ni‐O bonding in [Ce‐O‐Ni] site, thereby activating lattice oxygen redox of NiCo2O4 in OER.

Importing Atomic Rare-Earth Sites to Activate Lattice Oxygen of Spinel Oxides for Electrocatalytic Oxygen Evolution.

Spinel oxides have emerged as highly active catalysts for the oxygen evolution reaction (OER). However, due to covalency competition, the OER process on spinel oxides often follows an arduous adsorbate evolution mechanism (AEM) pathway. Herein, we propose a novel rare-earth sites substitution strategy to tune the lattice oxygen redox of spinel oxides and bypass the AEM scaling relationship limitation. Taking NiCo2O4 as a model, the incorporation of Ce into the octahedral site induces the formation of Ce-O-M (M: Ni, Co) bridge, which triggers charge redistribution in NiCo2O4. The developed Ce-NiCo2O4 exhibits remarkable OER activity with a low overpotential, satisfactory electrochemical stability, and good practicability in anion-exchange membrane water electrolyzer. Theoretical analyses reveal that OER on Ce-NiCo2O4 surface follows a more favorable lattice oxygen mechanism (LOM) pathway and non-concerted proton-electron transfers compared to pure NiCo2O4, as further verified by pH-dependent behavior and in situ Raman analysis.18O-labeled electrochemical mass spectrometry directly demonstrates that oxygen originates from the lattice oxygen of Ce-NiCo2O4 during OER. It is discovered that electron delocalization of Ce 4f states triggers charge redistribution in NiCo2O4 through the Ce-O-M bridge, favoring antibonding state occupation of Ni-O bonding in [Ce-O-Ni] site, thereby activating lattice oxygen redox of NiCo2O4 in OER.

Insight into Structure, Regulatable Photoluminescence of Stably Self and Codoped Phosphor Ba3Y2B6O15: Dy/Eu for nUV wLEDs

AbstractThe exploitation of borate‐based phosphors is garnered tremendous attention in wLEDs. Although previous research provided some insights into borates from the viewpoints of synthesis, structure, and defect evolutions, their photoluminescence (PL) with dopants is still insufficient for actual application, especially on aspects of efficiency/stability. Herein, to alleviate the above issues, a new type of lesser‐known high symmetry Ba3Y2B6O15 (BYB) codoped with Dy3+/Eu3+ phosphors are synthesized via multistep solid‐state reaction and possessed controllable PL based on nUV excitation, defect‐induced (self‐) PL, and energy transfer (ET) from Dy3+ to Eu3+. The origin of blue self‐PL is clarified based on oxygen‐related defects and optimized via adjusting synthetic atmosphere (air/Ar) and (co)doping dopants to control the defect content. Thanks to dense connectivity, and highly symmetric structure with perfectly ordered octahedral sites of Y3+ for accommodation of Dy/Eu and ET, “cool” white and red PL from Dy3+ and Eu3+, respectively, show high PL efficiency with narrow full width at half the maximum (fwhm). The phosphor also exhibits excellent thermal stability because of high bandgap and low electron‐phonon coupling. Finally, a high‐quality phosphor‐converted wLED (pc‐wLED) device is assembled via remote “capping” packaging by adopting the BYB: Dy/Eu and a 350 nm nUV LED chip.

Tunable annealing temperature for the structural, magnetic, optical, and dielectric characteristics of Mn0.5Zn0.5Ni0.5Fe1.5O4 nano-ferrite

The as-prepared Mn0.5Zn0.5Ni0.5Fe1.5O4 ferrite was prepared by the co-precipitation process and annealed at 300, 500, 900, and 1100 °C. The single-phase cubic spinel structure was confirmed by XRD patterns, Rietveld fitting, TEM imaging and several structural parameters, including crystalline size and lattice constant have been examined. The FTIR spectrum confirmed the main two absorption bands of tetrahedral and octahedral sites in ferrite, where the elastic parameters such as force constants and Debye temperature have been investigated. The saturation magnetization increases with the annealing temperature, while the energy band gap decreases with the annealing temperature, and also the ac conductivity decreases with annealing temperature.