Oxygen‐Deficient Ferric Oxide as an Electrochemical Cathode Catalyst for High‐Energy Lithium–Sulfur Batteries

Lithium–sulfur batteries, as one of promising next‐generation energy storage devices, hold great potential to meet the demands of electric vehicles and grids due to their high specific energy. However, the sluggish kinetics and the inevitable “shuttle effect” severely limit the practical application of this technology. Recently, design of composite cathode with effective catalysts has been reported as an essential way to overcome these issues. In this work, oxygen‐deficient ferric oxide (Fe₂O_3?x), prepared by lithiothermic reduction, is used as a low‐cost and effective cathodic catalyst. By introducing a small amount of Fe₂O_3?x into the cathode, the battery can deliver a high capacity of 512 mAh g^?1 over 500 cycles at 4 C, with a capacity fade rate of 0.049% per cycle. In addition, a self‐supporting porous S@KB/Fe₂O_3?x cathode with a high sulfur loading of 12.73 mg cm^?2 is prepared by freeze‐drying, which can achieve a high areal capacity of 12.24 mAh cm^?2 at 0.05 C. Both the calculative and experimental results demonstrate that the Fe₂O_3?x has a strong adsorption toward soluble polysulfides and can accelerate their subsequent conversion to insoluble products. As a result, this work provides a low‐cost and effective catalyst candidate for the practical application of lithium–sulfur batteries.     

Metal–Organic Gel‐Derived FexOy/Nitrogen‐Doped Carbon Films for Enhanced Lithium Storage

The development of cost‐effective and flexible electrodes is demanding in the field of energy storage. Herein, flexible Fe_xO_y/nitrogen‐doped carbon films (Fe_xO_y/NC‐MOG) are prepared by facile electrospinning of Fe‐based metal–organic gels (MOGs) followed by high‐temperature carbonization. This approach allows the even mixing of fragile coordination polymers with polyacrylonitrile into flexible films while reserving the structural characteristics of coordination polymers. After thermal treatment, Fe_xO_y/NC‐MOG films possess uniformly distributed Fe_xO_y nanoparticles and larger accessible surface areas than traditional Fe_xO_y‐NC films without MOG. Taking advantage of the unique structure, Fe_xO_y/NC‐MOG exhibits a superior rate performance (449.8 mA h g^?1 at 5000 mA g^–1) and long cycle life (629.3 mA h g^–1 after 500 cycles at 1000 mA g^–1) when used as additive‐free anodes in lithium‐ion batteries.     

Enhanced giant dielectric response in Sr[(Fe0.5Nb0.5)1−xTix]O3 solid solutions

In the present work, the modified dielectric relaxations with extended giant dielectric constant step were observed in Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions. The structure of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions changed from orthorhombic to cubic with increasing x. A dielectric relaxation following Arrhenius law of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions was observed at lower temperature. The dielectric constant of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions decreased firstly and then increased with increasing SrTiO₃ content at 1 kHz, while the dielectric loss was suppressed monotonically. At x = 0.8, the dielectric loss at room temperature and 1 kHz was 0.16 which was much smaller than that for x = 0 (tanδ = 0.37), while the dielectric constant was increased to 6,815, and the temperature stability was also improved. This indicated that the dielectric characteristics of Sr(Fe_0.5Nb_0.5)O₃ ceramics could be significantly improved by forming solid solution with SrTiO₃.     

Bimetallic Metal‐Organic Frameworks: Probing the Lewis Acid Site for CO2 Conversion

A highly porous metal‐organic framework (MOF) incorporating two kinds of second building units (SBUs), i.e., dimeric paddlewheel (Zn₂(COO)₄) and tetrameric (Zn₄(O)(CO₂)₆), is successfully assembled by the reaction of a tricarboxylate ligand with Zn^II ion. Subsequently, single‐crystal‐to‐single‐crystal metal cation exchange using the constructed MOF is investigated, and the results show that Cu^II and Co^II ions can selectively be introduced into the MOF without compromising the crystallinity of the pristine framework. This metal cation‐exchangeable MOF provides a useful platform for studying the metal effect on both gas adsorption and catalytic activity of the resulted MOFs. While the gas adsorption experiments reveal that Cu^II and Co^II exchanged samples exhibit comparable CO₂ adsorption capability to the pristine Zn^II‐based MOF under the same conditions, catalytic investigations for the cycloaddition reaction of CO₂ with epoxides into related carbonates demonstrate that Zn^II‐based MOF affords the highest catalytic activity as compared with Cu^II and Co^II exchanged ones. Molecular dynamic simulations are carried out to further confirm the catalytic performance of these constructed MOFs on chemical fixation of CO₂ to carbonates. This research sheds light on how metal exchange can influence intrinsic properties of MOFs.     

Multishelled NixCo3–xO4 Hollow Microspheres Derived from Bimetal–Organic Frameworks as Anode Materials for High‐Performance Lithium‐Ion Batteries

Metal–organic frameworks (MOFs) featuring versatile topological architectures are considered to be efficient self‐sacrificial templates to achieve mesoporous nanostructured materials. A facile and cost‐efficient strategy is developed to scalably fabricate binary metal oxides with complex hollow interior structures and tunable compositions. Bimetal–organic frameworks of Ni‐Co‐BTC solid microspheres with diverse Ni/Co ratios are readily prepared by solvothermal method to induce the Ni _x Co_{3? x} O₄ multishelled hollow microspheres through a morphology‐inherited annealing treatment. The obtained mixed metal oxides are demonstrated to be composed of nanometer‐sized subunits in the shells and large void spaces left between adjacent shells. When evaluated as anode materials for lithium‐ion batteries, Ni _x Co_{3? x} O₄‐0.1 multishelled hollow microspheres deliver a high reversible capacity of 1109.8 mAh g^?1 after 100 cycles at a current density of 100 mA g^?1 with an excellent high‐rate capability. Appropriate capacities of 832 and 673 mAh g^?1 could also be retained after 300 cycles at large currents of 1 and 2 A g^?1, respectively. These prominent electrochemical properties raise a concept of synthesizing MOFs‐derived mixed metal oxides with multishelled hollow structures for progressive lithium‐ion batteries.     

Giant dielectric permittivity and room temperature magnetodielectric study of BaTi0.2(Fe0.5Nb0.5)0.8O3 nanoceramic

BaTi_0.2(Fe_0.5Nb_0.5)_0.8O₃ [BTFN] ceramic was prepared by sol–gel method. X-ray diffraction pattern of the sample at room temperature shows a cubic phase. Microstructure analysis shows well-grown and dense grains in the sintered sample. High dielectric constant (∼15,000) with low loss (∼0.6) was found at room temperature at 1 kHz frequency. Cole–Cole plot analysis shows that the grain boundary effect (barrier layer formation) is responsible for such a high value of dielectric constant. Another interesting feature of BTFN ceramic is the appearance of room temperature high magnetodielectric response (∼8%) at 9 kOe magnetic field. Magnetodielectric effect was observed in the sample which is due to the Maxwell–Wagner polarization along with magnetoresistance.     

Studies on the solid solutions,LnV1−xMxO3 (Ln:La,Gd or Y,M:Cr or Fe)

Electrical and magnetic properties of the solid solutions LnV_1?xM_xO₃ (Ln:La, Gd or Y, M:Cr or Fe) were studied in the temperature range 77–1000K. These solid solutions were all semiconductors. Their conductivity at room temperature decreased with Cr³⁺ or Fe³⁺ ion concentrations. The solid solutions LaV_1?xM_xO₃ and YV_1?xM_xO₃ (M:Cr or Fe) revealed an antiferromagnetism with a weak ferromagnetism and their ordering temperature increased with x. Most of the gadolinium-containing compounds were paramagnets in the measured temperature range. YV_0.4Fe_0.6O₃ showed a thermal hysteresis at high temperatures.     

Demonstration of a Broadband Photodetector Based on a Two-Dimensional Metal–Organic Framework

Metal–organic frameworks (MOFs) are emerging as an appealing class of highly tailorable electrically conducting materials with potential applications in optoelectronics. Yet, the realization of their proof-of-concept devices remains a daunting challenge, attributed to their poor electrical properties. Following recent work on a semiconducting Fe₃(THT)₂(NH₄)₃ (THT: 2,3,6,7,10,11-triphenylenehexathiol) 2D MOF with record-high mobility and band-like charge transport, here, an Fe₃(THT)₂(NH₄)₃ MOF-based photodetector operating in photoconductive mode capable of detecting a broad wavelength range from UV to NIR (400–1575 nm) is demonstrated. The narrow IR bandgap of the active layer (≈0.45 eV) constrains the performance of the photodetector at room temperature by band-to-band thermal excitation of charge carriers. At 77 K, the device performance is significantly improved; two orders of magnitude higher voltage responsivity, lower noise equivalent power, and higher specific detectivity of 7 × 10⁸ cm Hz^1/2 W⁻¹ are achieved under 785 nm excitation. These figures of merit are retained over the analyzed spectral region (400–1575 nm) and are commensurate to those obtained with the first demonstrations of graphene- and black-phosphorus-based photodetectors. This work demonstrates the feasibility of integrating conjugated MOFs as an active element into broadband photodetectors, thus bridging the gap between materials' synthesis and technological applications.     

Röntgenographische und mössbauer-spektroskopische untersuchungen am system Fe1+xYb2−xS4

Polycristalline samples of the system Fe_1+xYb_2?xS₄ have been investigated in the range 0,0 ≤ x ≤ 0,4 in both the low temperature structure and the spinel-type high temperature structure. The lattice constants of the spinels decrease linearly with increasing x; the tetrahedral sites are occupied by iron only. The valence distribution Fe⁺² Fe⁺³_xYb⁺³_2?x S^?2₄ and a slight distortion of the spinel lattice are concluded from the Mößbauer parameters at room temperature.     

Spin‐Orbit Torque Switching of a Nearly Compensated Ferrimagnet by Topological Surface States

Utilizing spin‐orbit torque (SOT) to switch a magnetic moment provides a promising route for low‐power‐dissipation spintronic devices. Here, the SOT switching of a nearly compensated ferrimagnet Gd_x(FeCo)_1?x by the topological insulator [Bi₂Se₃ and (BiSb)₂Te₃] is investigated at room temperature. The switching current density of (BiSb)₂Te₃ (1.20 × 10⁵ A cm^?2) is more than one order of magnitude smaller than that in conventional heavy‐metal‐based structures, which indicates the ultrahigh efficiency of charge‐spin conversion (>1) in topological surface states. By tuning the net magnetic moment of Gd_x(FeCo)_1?x via changing the composition, the SOT efficiency has a significant enhancement (6.5 times) near the magnetic compensation point, and at the same time the switching speed can be as fast as several picoseconds. Combining the topological surface states and the nearly compensated ferrimagnets provides a promising route for practical energy‐efficient and high‐speed spintronic devices.     

Magnetic properties of Y2Fe17?x Gax and Sm2Fe17?xGax compounds

The magnetic properties of Y₂Fe_17−x Ga_x and Sm₂Fe_17−xGa_x for 3 ≤ x ≤ 7 have been investigated using the ⁵⁷Fe M?ssbauer spectroscopy at room temperature. These compounds have the rhombohedral Th₂Zn₁₇ structure. X-ray diffraction analyses of aligned powders show that the easy direction of magnetization is parallel to the c-axis in Y₂Fe₁₀Ga₇ and Sm₂Fe₁₄Ga₃ and is perpendicular to the c-axis in Y₂Fe₁₄Ga₃, Y₂Fe₁₂Ga₅, Sm₂Fe₁₂Ga₅ and Sm₂Fe₁₀Ga₇. M?ssbauer studies indicate that all the samples studied are ferromagnetically ordered. The ⁵⁷Fe hyperfine field decreases with increasing Ga content. This decrease results from the decreased magnetic exchange interactions resulting from Ga substitution. The average isomer shift, δ, for Y₂Fe_17−xGa_x and Sm₂Fe_17−xGa_x at room temperature is positive and the magnitude of δ increases with increasing Ga content.     

Structural,magnetic, and magnetodielectric correlations in multiferroic Bi5Ti3FeO15

We have investigated the structural, magnetic, magnetodielectric, and magnetoimpedance characteristics of Aurivillius-structured Bi₅Ti₃FeO₁₅ (BTFO) synthesized by a generic solid-state reaction route. Rietveld refinement of X-ray diffraction pattern at room temperature (RT) confirms orthorhombic crystal structure (space group A2₁am). In BTFO, octahedral distortion of the perovskite unit occurs due to antisite defects Fe/Ti in the BO₆ site, which results in the formation of Fe–O clusters. Raman spectra also reveal Ti/FeO6 octahedral distortion due to the vibration of Bi ions in the perovskite layer. Magnetic field-dependent magnetization (M–H) and electric field-dependent polarization (P–E) measurement at RT indicate the existence of multiferroic behavior in BTFO. The M–H hysteresis at 5 K suggests that the non-interacting superparamagnetic state is dominant over the local short-range antiferromagnetic (AFM) ordering. The AFM interaction arises due to the random distribution of antisite defects Fe/Ti causing the distorted Fe–O octahedral unit. These canted spin interact via the Dzyaloshinskii–Moriya (DM) interaction. The superexchange interaction between the Fe–O–Fe ions is stronger than the next-nearest-neighboring Fe–O–O–O–Fe interaction. This happens due to the intermediate fluorite-like layer (Bi₂O₂)²⁺, which opposes the long-range exchange interaction. The negative magnetodielectric (MD) effect is more prominent at low frequency (~?100 Hz) due to the extrinsic contribution. In contrast, in the high-frequency region (>?50 kHz), the intrinsic contribution dominates, which is further ascertained by magnetoimpedance (MI) measurement. The maximum magnitude of the MD effect is found to be?~?0.32% at a magnetic field of 13 kOe at 150 K. Lastly, the ferroelectric characteristic of the sample is obtained from the P–E measurement with a polarization value of 4.35 µC/cm² with an applied electric field of 70 kV/cm.

     

Room‐Temperature Ferromagnetic Insulating State in Cation‐Ordered Double‐Perovskite Sr2Fe1+xRe1−xO6Films

Ferromagnetic insulators (FMIs) are one of the most important components in developing dissipationless electronic and spintronic devices. However, FMIs are innately rare to find in nature as ferromagnetism generally accompanies metallicity. Here, novel room‐temperature FMI films that are epitaxially synthesized by deliberate control of the ratio between two B‐site cations in the double perovskite Sr₂Fe_1+xRe_1‐xO₆ (?0.2 ≤ x ≤ 0.2) are reported. In contrast to the known FM metallic phase in stoichiometric Sr₂FeReO₆, an FMI state with a high Curie temperature (T_c ≈ 400 K) and a large saturation magnetization (M_S ≈ 1.8 µ_B f.u.^?1) is found in highly cation‐ordered Fe‐rich phases. The stabilization of the FMI state is attributed to the formation of extra Fe³⁺? Fe³⁺ and Fe³⁺? Re⁶⁺ bonding states, which originate from the relatively excess Fe ions owing to the deficiency in Re ions. The emerging FMI state created by controlling cations in the oxide double perovskites opens the door to developing novel oxide quantum materials and spintronic devices.     

X-ray diffraction,Mössbauer spectrometry and thermal studies of the mechanically alloyed (Fe1−xMnx)2P powders

(Fe_1?xMn_x)₂P phosphide powders in the composition range 0.15?≤?x ≤ 0.75 have been mechanically alloyed and their structural, magnetic and thermal changes with composition have been investigated by means of X-ray diffraction, ⁵⁷Fe Mössbauer spectrometry, magnetization measurements and differential scanning calorimetry. The milling process induces changes in the crystal phase diagram of the (Fe_1?xMn_x)₂P system. The XRD results reveal the coexistence of a bcc Fe(Mn)-type, hexagonal (Fe₂P and Mn₂P-type), orthorhombic (MnP-type) and tetragonal Fe₃P-type structures for all compositions. The room temperature Mössbauer spectra confirm the formation of the Fe(Mn)-type, non-stoichiometric Fe₂P-type, FeP-type and Fe₃P-type structures. Saturation magnetization exhibits a comparable behavior to that of the average hyperfine magnetic field. The DSC scans show the existence of several endothermic and exothermic peaks in the temperature range (100–700)?°C related to different phase transitions. The endothermic peak at about 582–589?°C can be related to the ferromagnetic/paramagnetic transition temperature (Curie temperature, T_C) of the Fe(Mn)-type structure.     

Structural,optical and magnetic properties of the Fe2TiO5 nanopowders

Iron titanate nanopowders with a particle size range of 48–70?nm could be obtained after calcinations of the dried gel at 900°C for 2?h. Fe₂TiO₅ indicates a ferrimagnetic–paramagnetic behaviour, as evidenced by using vibrating sample magnetometer at room temperature. In the temperature range of 25–300°C the empirical equation of the heat capacity C _p (J/mol?K)?=??692.328?+?1.39?T?+?3.757?×?10⁷/T ² for Fe₂TiO₅ was determined from differential scanning calorimetry. Direct optical band gap of Fe₂TiO₅ was calculated using the Tauc model by UV-Vis diffuse reflectance spectroscopy. Band gap energy of Fe₂TiO₅ was determined as 1.95?eV.     

Effect of Sm3+ on dielectric and magnetic properties of Y3Fe5O12 nanoparticles

The Sm³⁺ doped Y_3?xSm_xFe₅O₁₂ (x = 0–3) nanopowders were prepared using modified sol–gel route. The crystalline structure and morphology was confirmed by X-ray diffraction and atomic force microscopy. The nanopowders were sintered at 950 °C/90 min using microwave sintering method. The lattice parameters and density of the samples were increased with an increase of Sm³⁺ concentration. The room temperature dielectric (ε′ and ε″) and magnetic (μ′ and μ″) properties were measured in the frequency range up to 20 GHz. The room temperature magnetization studies were carried out using Vibrating sample magnetometer using filed of 1.5 T. Results of VSM show that the saturation and remnant magnetization of Y_3?xSm_xFe₅O₁₂ (0–3) decreases on increasing the Sm concentration (x). The low values of magnetic (μ′ and μ″) properties makes them a good candidates for microwave devices, which can be operated in the high frequency range.     

Negative thermal expansion induced by intermetallic charge transfer

Abstract

Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu₃Fe₄O₁₂ and LaCu₃Fe_4?xMn_xO₁₂, as well as in Bi or Ni substituted BiNiO₃. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding ?70 × 10^?6 K^?1 near room temperature, in the temperature range which can be controlled by substitution.     

Temperature dependence on the mass susceptibility and mass magnetization of superparamagnetic Mn–Zn–ferrite nanoparticles as contrast agents for magnetic imaging of oil and gas reservoirs

The mass susceptibility (χ_mass) and mass magnetization (M_mass) were determined for a series of ternary manganese and zinc ferrite nanoparticles (Mn–Zn ferrite NPs, Mn_xZn_1?xFe₂O₄) with different Mn:Zn ratios (0.08 ≤ x ≤ 4.67), prepared by the thermal decomposition reaction of the appropriate metal acetylacetonate complexes, and for the binary homologs (M_xFe_3?xO₄, where M = Mn or Zn). Alteration of the Mn:Zn ratio in Mn–Zn ferrite NPs does not significantly affect the particle size. At room temperature and low applied field strength the mass susceptibility increases sharply as the Mn:Zn ratio increases, but above a ratio of 0.4 further increase in the amount of manganese results in the mass susceptibility decreasing slightly, reaching a plateau above Mn:Zn ≈ 2. The compositional dependence of the mass magnetization shows less of a variation at room temperature and high applied fields. The temperature dependence of the mass magnetization of Mn–Zn ferrite NPs is significantly less for Mn-rich compositions making them more suitable for downhole imaging at higher temperatures (>100 °C). For non-shale reservoirs, replacement of nMag by Mn-rich Mn–Zn ferrites will allow for significant signal-to-noise enhancement of 6.5× over NP magnetite.     

Investigation of Cs(H2PO4)1 − x (HSO4) x (x = 0.15–0.3) superprotonic phase stability

A detailed investigation of the highly conductive Cs(H₂PO₄)_1?x (HSO₄) _x (x = 0.15–0.3) proton electrolyte, its structural properties, and ageing behavior was carried out using X-ray diffraction, DSC, and impedance and NMR spectroscopy. The high conductivity of electrolytes (～2 × 10^?2 S/cm) remains stable during long-term ageing at 180–200°C due to stabilization of the high temperature phase to lower temperatures. The room temperature ¹H MAS NMR spectrum of (CsH₂PO₄)_1?x (CsHSO₄) _x demonstrates the predominantly highly mobile protons present in these materials with the residual low-mobile protons, which agrees with the XRD data. According to XRD and ¹H NMR data, the cubic phase of Cs(H₂PO₄)_{1 ? x} (HSO₄) _x (x = 0.15–0.3) that stabilizes at room temperature gradually transforms to a low-temperature monoclinic one. The kinetics of the phase transformation for mixed salt depends markedly on the relative air humidity. A possible stabilization mechanism of the Cs(H₂PO₄)_{1 ? x} (HSO₄) _x superionic phase with high proton mobility at low temperatures is discussed.     

Gd5(SixGe1–x)4: An Extremum Material

The large shear displacements of atomic layers in Gd₅(Si_xGe_1–x)₄ materials, coupled with the change of crystallographic symmetry and magnetic order, characterizes these transformations as magnetic–martensitic, which are extremely rare. The start and the end of the magnetic–martensitic transitions depends strongly on the direction of change (i.e., increasing or decreasing) of either or both the temperature and magnetic field. These profound bonding, structural, electronic, and magnetic changes, which occur in the Gd₅(Si_xGe_1–x)₄ system, bring about some extreme changes of the materials' behavior resulting in a rich variety of unusually powerful magneto‐responsive properties, such as the giant magnetocaloric effect, colossal magnetostriction, and giant magnetoresistance.