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Mass transport in bulk spinel ferrites NiFe2O4 is studied computationally using the kinetic activation–relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm. Diffusion mechanisms—difficult to observe with molecular dynamics—are described by k-ART. Point defects are assumed to be responsible for ionic diffusion; thus, both cation and anion defects are investigated. This work focuses on vacancies and interstitials by comparing their properties with two Buckingham potential parameterizations: one with nominal charges and the other with partial charges. Both potentials are corrected at short distances, thus allowing interstitial diffusion and avoiding the catastrophic infinite energies appearing with Buckingham at short distances. The energy landscape along different pathways is described in detail. Both potentials predict the same mechanisms but different migration energies. Mechanisms by which a normal spinel is transformed to an inverse spinel via cation diffusion are unveiled, and diffusion coefficients are predicted. We find that interstitial Ni diffusion involves the movement of two Ni ions and that O interstitials trigger a collective diffusion of O ions, while an O vacancy diffuses by an O ion moving to the center of a cuboctahedron. [ABSTRACT FROM AUTHOR]

Recently, LiGa 5 O 8 was identified as a cubic spinel type ultra-wide-bandgap semiconductor with a gap of about 5.36 eV and reported to be unintentionally p -type. Here, we present first-principles calculations of native defects and their various complexes to try to explain the occurrence of p -type doping. Although we find Li vacancies (0.74 eV above VBM) to be shallower acceptors than in LiGaO 2 (1.63 eV above VBM), and becoming slightly shallower in complexes with donors such as V O (0.58 eV above VBM) and Ga Li antisites (0.65 eV above VBM), these V Li based defects are not sufficiently shallow to explain p -type doping. The dominant defects are donors and, in equilibrium, the Fermi level would be determined by compensation between donors and acceptors and pinned deep in the gap. [ABSTRACT FROM AUTHOR]

Recently, LiGa 5 O 8 was identified as a cubic spinel type ultra-wide-bandgap semiconductor with a gap of about 5.36 eV and reported to be unintentionally p -type. Here, we present first-principles calculations of native defects and their various complexes to try to explain the occurrence of p -type doping. Although we find Li vacancies (0.74 eV above VBM) to be shallower acceptors than in LiGaO 2 (1.63 eV above VBM), and becoming slightly shallower in complexes with donors such as V O (0.58 eV above VBM) and Ga Li antisites (0.65 eV above VBM), these V Li based defects are not sufficiently shallow to explain p -type doping. The dominant defects are donors and, in equilibrium, the Fermi level would be determined by compensation between donors and acceptors and pinned deep in the gap. [ABSTRACT FROM AUTHOR]

The effects of isothermal annealing on the self-assembled nanostructures of spinel manganese oxide ZnMnGaO4 were investigated using transmission electron microscopy and x-ray diffraction. The checkerboard nanostructures and zigzag nanostructures (named "Sierra" nanostructures) coexisted owing to the chemical phase separation of Mn3+ and Ga3+ ions by isothermal annealing at 575 °C. It was observed that the checkerboard nanostructures were dominant in short-time annealing and that the volume fraction of the Sierra nanostructures became more prominent as the annealing period increase. The interdiffusion of Mn3+ and Ga3+ is indicated to play an important role in gaining the total energy of the system by the reduction in the local strain caused by the formation of nanostructures. These results provide further insights into the fabrication of distinct types of nanostructures in complex transition-metal compounds. [ABSTRACT FROM AUTHOR]

The effects of isothermal annealing on the self-assembled nanostructures of spinel manganese oxide ZnMnGaO4 were investigated using transmission electron microscopy and x-ray diffraction. The checkerboard nanostructures and zigzag nanostructures (named "Sierra" nanostructures) coexisted owing to the chemical phase separation of Mn3+ and Ga3+ ions by isothermal annealing at 575 °C. It was observed that the checkerboard nanostructures were dominant in short-time annealing and that the volume fraction of the Sierra nanostructures became more prominent as the annealing period increase. The interdiffusion of Mn3+ and Ga3+ is indicated to play an important role in gaining the total energy of the system by the reduction in the local strain caused by the formation of nanostructures. These results provide further insights into the fabrication of distinct types of nanostructures in complex transition-metal compounds. [ABSTRACT FROM AUTHOR]

We regulate the particle size and crystallographic facet of single-crystal (SC) Li(Ni,Mn) 2 O 4 (LNMO) cathode materials via flux-selective molten salt method. By simply adjusting Li 2 MoO 4 or LiI as sintering aids, we synthesized size controlled SC particles, both small and large, and comparatively investigated their electrochemical behavior focusing on the lithiation/delithiation reactivity in conjunction with the particle size and surface planes. Considering the growth mechanism of a SC particles with a specific crystal plane, such particle size control is not determined solely by the synthetic condition but must also consider the interfacial energy of the crystal planes in conjunction with the fluxes what we used. While the initial charge capacity is similar, the given cathode using a small SC LNMO (using LiI) with uniform particle sizes (≤5 μm) exhibits outstanding rate capability with stable capacity retention under changing current density, which indicates stable lithium transport during the repetitive electrochemical reactions. The dependency of the impedance response with change in the electrode resistances as well as the stability during the cycle reactions in conjunction with the post-mortem Li distribution by using laser-induced breakdown spectroscopy as a function of porosity change and cell degradation are thoroughly discussed from the standpoint of regulated particle property. [ABSTRACT FROM AUTHOR]

The composite catalyst improved the combustion performance by combining the advantages of multiple catalysts. In this paper, a high-efficiency methane catalytic combustion burner was designed for hydrogen production. The spinel of CoX 2 O 4 (X = Al, Fe, Cr, Cu) was prepared to composite with hexaaluminate. And the effects of temperature distribution and gas production were investigated under different operating conditions for these catalysts. The results indicated that the single-metal Mn catalyst facilitated the dry reforming reaction to produce more syngas. In addition, the hydrogen mole fraction first increased and then decreased with the increasing of Mn substitution, which achieved the maximum value of 12.6% at the Mn substitution of 3. Compared with the single catalyst, the synergistic effect of the bimetals reduced the activation energy of the methane reaction. And the Mn and Fe bimetal-substituted had excellent hydrogen production properties. However, the interaction between Co and Mn ions was not conducive to the doped dispersion of the catalyst and inhibited the catalytic activity. Meanwhile, higher inlet velocity and equivalence ratio increased the combustion temperature and syngas production. • Hexaaluminate and spinel catalysts were combined to enhance the catalytic performance. • Increasing the substitution ratio weakened the redox effect of hexaaluminate. • Bimetal-substituted hexaaluminate significantly reduced the preheating time. • CoCr 2 O 4 exhibited the highest Co3+/(Co3++Co2+) ratio and greatly activated methane. [ABSTRACT FROM AUTHOR]

Understanding the origin of surface reconstruction is crucial for developing highly efficient lattice oxygen oxidation mechanism (LOM) based spinel oxides. Traditionally, the reconstruction has been achieved through electrochemical procedures, such as cyclic voltammetry (CV), linear sweep voltammetry (LSV). In this work, we found that the surface reconstruction in LOM‐based CoFe0.25Al1.75O4 catalyst was an irreversible oxygen redox chemical reaction. And a lower oxygen vacancy formation energy (EO‐V) could benefit the combination of the activated lattice oxygen atoms with adsorbed water molecular. Motivated by this finding, a strategy of phase boundary construction from Co tetrahedral to octahedral was employed to decrease EO‐V in CoFe0.25Al1.75O4. The results showed that as the Co octahedral occupancy ratio rose to 64 %, a 3.5 nm‐thick reconstructed layer formed on the catalyst surface with a 158 mV decrease in overpotential. Further experiments indicated that the coexistence of tetrahedral‐octahedral (O−T) phase would result in lattice mismatch, promoting non‐bonding oxygen states and lowering EO‐V. Then more active lattice oxygen combined with H2O molecules to generate hydroxide ions (OH−), followed by soluble cation leaching, which enhanced the reconstruction process. This work provided new insights into the relationship between the intrinsic structure of pre‐catalysts and surface reconstruction in LOM‐based spinel electrocatalysts. [ABSTRACT FROM AUTHOR]

The photocatalytic properties of CoFe2O4 nanoparticles were activated by the doping and co-doping of a low level of Y3+ and Sm3+ cations. After optimizing the annealing temperature, 900 °C was found to be the optimal temperature for the successful incorporation of Y3+ and Sm3+ into the spinel structure. The purity of our samples annealed at 900 °C was confirmed using several characterization methods, including PXRD, SEM, XPS, VSM, FTIR, and Raman spectroscopy. Thus, we were able to increase the photocatalytic degradation of orange G dye from 9.9 to 64.63% for the Sm3+-doped sample, 76.42% for the Y3+-doped sample, and even 85.81% for the co-doped sample under 60 min of UV–visible light irradiation. The beneficial effect of samarium and yttrium doping and co-doping is attributed to several factors: the first factor is doped and co-doped rare earth impurities induce distortion in the lattice, the larger the ionic radii of dopant element, the highest is the photocatalytic activity; second factor, upon doping and co-doping of rare earth impurities in the structure of CoFe2O4 leads to the creation of donor state level within the band gap, causing the Fermi energy to shift near the conduction band. Third factor, co-doping produced strong interactions, which accelerated photocarrier mobility and transport; lastly, longer electron-holes lifetime. We have provided a detailed study of the structural, vibrational, and optical properties to support our conclusions. [ABSTRACT FROM AUTHOR]

As a high energy density cathode material, further development of high working voltage spinel LiNi0.5Mn1.5O4 has hindered by its rapid capacity degradation. To address this, a hetero-valent substitution of magnesium for manganese was used to synthesize spinel LiNi0.5MgxMn1.5−xO4 (x = 0, 0.03, 0.05) via a microwave sol-gel method. XRD and refined results indicate that such strategy leads to the modification of the 16c interstitial sites. The electrical performance demonstrates that a modest substitution (x = 0.03) significantly improves both rate performance (113.1 mAh/g, charge and discharge at 5 C) and cycling stability (85% capacity retention after 500 cycles at 1 C). A higher substitution level (x = 0.05) markedly improves high-rate cycling performance, achieving 96% capacity retention after 500 cycles at 5 C. It offers tailored solutions for various application needs, including capacity-focused and high-current-rate applications. Furthermore, the stable LiNi0.5Mg0.05Mn1.45O4 sample could also serve as an effective coating layer for other electrode materials to enhance their cycling stability. [ABSTRACT FROM AUTHOR]

CoxMn3−xO4 (1 ≤ x ≤ 2) spinel nanoparticles synthesized through conventional coprecipitation technique exhibit the coexistence of tetragonal and cubic phases in the range of 1 ≤ x ≤ 1.5, while a pure cubic phase is observed for 1.75 ≤ x ≤ 2 at room temperature. Reduction in tetragonal phase fraction from 92 % for x = 1 to 47% for x = 1.5 is attributed to diminution of Jahn–Teller (J–T) active Mn3+ ions occupying the octahedral site of spinel lattice. X‐ray photoelectron spectroscopy confirms both +2 and +3 oxidation states for Co and Mn. Surprisingly, cubic and tetragonal phases exhibit magnetic transition, Tc1 and Tc2, corresponding to a paramagnetic to a high and low temperature ferrimagnetic state, respectively. Tetragonal phase induces high spontaneous (HSEB) and conventional (HCEB) exchange bias with unusually high vertical magnetization shift (VMS) than that of the pure cubic phase, shows maximum HCEB of 4.062 kOe for x = 1.5 and a VMS of 2.5 emu g−1 for x = 1. Such dependence of VMS and exchange bias on tetragonal to cubic phase ratio in CoxMn3−xO4 is demonstrated for the first time and interpreted based on the interaction between different arrangement of spins in tetrahedral and octahedral sublattice. [ABSTRACT FROM AUTHOR]

Zinc‐ion batteries (ZIBs) are promising grid‐scale energy storage devices owing to their low cost, high energy/power densities, high safety, benign environmental impact, etc. Among various cathode materials, ZnMn2O4 spinel has attracted attention because of its high theoretical capacity (448 mAh g−1) associated with the two‐electron redox reaction of Mn ions (2+/4+), a higher voltage (≈1.4 V vs Zn/Zn2+) than V2O5‐based cathodes (≈1.0 V), and better cyclability among manganese oxide‐based cathodes. However, so far only the one‐electron reaction of Mn ions is used with ZnMn2O4 spinel (≈224 mAh g−1), impairing its attractive features. In this study, the two‐electron reaction is successfully enabled by synthesizing ultrasmall ZnMn2O4 spinel nanoparticles (≈5 nm) composited with graphene (US‐ZMO/G) via a rapid room‐temperature alcohol reduction process, achieving the reversible capacity of 445 mAh g−1 at the second cycle. As far as it is known, the US‐ZMO/G composite achieves the highest gravimetric energy/power densities among cathodes for ZIBs. The combination of high capacity and high voltage enables an outstanding energy density approaching that of lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

High-entropy ceramics have sparked renewed interest in compositionally complex ceramics since the first introduction in 2015. The kaleidoscopic array of compositions and structures harnessed by this idea has unlocked an unprecedented opportunity to tailor materials for specific applications, including catalysis, thermal barriers, and electrochemical energy storage. Within the family of oxides, a competition exists between rock-salt and spinel structures. The rock-salt structure is highly symmetrical, consisting of a single cation sublattice, while the spinel structure offers more flexibility to accommodate various cations in two distinct sublattices. Herein, we aimed at stabilizing and expanding the thermal stability range of the spinel-structured oxide, successfully synthesizing novel, single-phase, compositionally complex materials by capitalizing on entropy stabilization, all while avoiding the ubiquitous use of nickel and chrome, notorious for their negative environmental impact. The right combination of cations resulted in the synthesis of a seven-metal oxide that is thermally stable up to the remarkable temperature of 1473 K. [ABSTRACT FROM AUTHOR]

In the current study, the effect of Cr 2 O 3 on the break temperature and crystallization behavior of Cr-containing molten titanium slag was investigated. The type, composition, and morphology of crystallized phase were analyzed by FactSage, X-ray diffraction (XRD), and scanning electron microscopy (SEM) combined with energy dispersive spectrometry (EDS). It was found that the break temperature (T Br) of Cr-containing molten titanium slag tended to increase with the increase of Cr 2 O 3 content. When the Cr 2 O 3 content was 4 wt%, the T Br was 1470 °C. With the increase of Cr 2 O 3 content, the Ti-containing phase began to appear at the temperature above the T Br. Moreover, the main crystallized phase that existed at the temperature below the T Br transformed from only anosovite to both anosovite and spinel, indicating that Cr 2 O 3 promoted the precipitation of spinel. The rapid increase in viscosity was mainly determined by the precipitation of anosovite in the slag without Cr 2 O 3. When the Cr 2 O 3 content was 2 wt%, the increased precipitation amount of Ti-containing phase caused the abrupt change in viscosity. As the Cr 2 O 3 content further increased to 4 wt%, the precipitation amounts of anosovite and spinel significant increased, which resulted in the sudden increase in viscosity. This study could provide theoretical support for the comprehensive utilization of Cr-containing molten titanium slag and sustainable development of titanium and chromium resources. [ABSTRACT FROM AUTHOR]

Plasma-based methods present a highly efficient approach for reclaiming valuable metals and nanoparticles from discarded metal scraps and minerals. In this research, we employed the thermal plasma arc discharge (TPAD) method to synthesize mixed-phase spinal-type magnesium aluminate and magnesium oxide (MgAl 2 O 4 /MgO) nanocomposites ranging in size from 10 to 120 nm, using discarded MgAl alloy waste scraps as the primary material. By employing comprehensive characterization techniques such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDS), we successfully confirmed the formation of highly crystalline MgAl 2 O 4 /MgO nanocomposites, showcasing a nearly spherical morphology. The surface area of the prepared nanocomposites was investigated using Brunauer-Emmett-Teller (BET) analysis; the values are 51.3 m2g-1. The synthesized MgAl 2 O 4 /MgO nanocomposites displayed exceptional photocatalytic activity toward industrial wastewater and commercial dye. Moreover, investigated the storage properties of MgAl 2 O 4 /MgO nanocomposites as an electrode material, revealing a good specific capacitance of 379.2 F/g at a current density of 1 A/g, demonstrating pseudocapacitive behavior. These results offer valuable insights into sustainable waste utilization and the development of high-performance nanomaterials for practical applications in various fields. [ABSTRACT FROM AUTHOR]

Bifunctional catalysts for oxygen evolution reduction (OER) and oxygen reduction reaction (ORR) are key renewable energy technologies including metal–air batteries and water splitting. In this work, a solid-state sintering approach was employed to prepare spinel-structured bimetallic oxides Co2GeO4 and Ni2GeO4 with remarkable bifunctional catalytic activity. Compared to Ni2GeO4 and Co3O4, Co2GeO4 demonstrates a larger density of oxygen vacancies, leading to an increased abundance of active sites and superior OER and ORR activities. Electrochemical measurements were carried out in alkaline media, the material requiring a mere overpotential of 263 mV to attain a current density of 10 mA cm−2. Moreover, Co2GeO4 exhibited exceptional stability, maintaining a stable potential for 40 h at a current density of 1 mA cm−2. The calculation revealed that the high stability is attributed to the robust Ge-O bonds, which stabilize the Ge-O4 tetrahedrons within the spinel framework. This study possesses significant potential in guiding the development of highly efficient bifunctional electrocatalysts for both OER and ORR. [ABSTRACT FROM AUTHOR]

The proportion of pellets in the blast furnace charge structure is gradually increasing, among which magnesium-bearing fluxed pellets have been widely applied due to their excellent metallurgical properties. To further determine the consolidation mechanism in different reaction layers of magnesium-bearing fluxed pellets, the phase transformation and diffusion behaviors of Fe3O4–MgO in different roasting atmospheres were investigated in this study. The results showed that Fe2+ preferentially diffused to the MgO layer and combined with Mg2+ to form MgyFe1−yO in inert atmosphere, and then, Fe3+ and Fe2+ binded to Mg2+ to form [(MgO)x(FeO)1−x]·Fe2O3 (0 ≤ x ≤ 1). The increase of roasting temperature was favorable for the entry of Mg2+ into the spinel phase. In air atmosphere, Fe3O4 was first oxidized to Fe2O3. Fe3+ and Mg2+ counter-diffused and then combined to MgxFe3−xO4 (x = 1). Fe3O4 reacted more readily with MgO in inert atmosphere than in air atmosphere. It was favorable to increase the oxygen partial pressure for MgxFe3−xO4 (x = 1) generation. The diffusion rate of Mg2+ at the interface of Fe3O4–MgO system in inert atmosphere was 1.88 µm/min at 1200 °C, which was faster than that of 1.49 µm/min in air atmosphere. [ABSTRACT FROM AUTHOR]

The development of cobalt‐free, high‐energy‐density cathode materials is an important prerequisite for the commercialization of the next generation of high‐energy‐density, cost‐effective lithium batteries. Co‐free spinel LiNi0.5Mn1.5O4 (LNMO) with simultaneous Ni and Mn multi‐cation redox reactions possesses a high theoretical specific capacity of 230 mAh g−1 and a theoretical energy density of 865 Wh kg−1. Unfortunately, LNMO cycled at 2.3–4.95 V suffered from severe interfacial dynamic evolution and electrolyte decomposition, leading to uncontrollable transition metal dissolution and a rapid decrease of reversible specific capacity. Here, It is demonstrated that the addition of an appropriate amount of lithium difluorophosphate (LiDFP) to a common carbonate‐based electrolyte can achieve stable cycling of LNMO in the voltage range of 2.3–4.95 V. The LNMO‐Li cell retained 82.8% of its initial capacity (175.2 mAh g−1) after 300 cycles. The improved cycle performance is attributed to the robust interface formed by the decomposition of LiDFP, which inhibits the dissolution of transition metals and the continued decomposition of the electrolyte. This work provides important insights for the development of the next generation of high‐energy‐density cobalt‐free lithium batteries. [ABSTRACT FROM AUTHOR]

In this work, MgO‐MgAl2O4 ceramic filters were fabricated from microporous MgO powder and α‐Al2O3 micro‐powder, in which microporous MgO powder was prepared using Mg(OH)2 as initial raw material. With the α‐Al2O3 micro‐powder content increased from 0 to 15 wt%, the tight packing and reaction sintering between MgO microparticles and Al2O3 microparticles promoted the formation and growth of magnesium aluminate spinel necks, reduced the apparent porosity of ceramic filter skeletons, decreased the pore size, and improved the strength of the filters. When the α‐Al2O3 micro‐powder content further raised to 20 wt%, the thermal mismatch between MgO microparticles and spinel microparticles caused a small amount of crack generation, which lowered the strength of the filter. Besides, after introducing the α‐Al2O3 micro‐powder, more spinel necks were produced due to a small amount of MgO solid dissolved in the spinel lattice during the thermal shock test, which enhanced the thermal shock resistance of the filters. When the α‐Al2O3 micro‐powder content was 15 wt%, the filter had excellent comprehensive performance, the bulk density and apparent porosity of the filter skeleton were 3.09 g/cm3 and 10.7%, and the compressive strength before and after thermal shock test was 3.48 and 3.70 MPa, respectively. [ABSTRACT FROM AUTHOR]

Grain boundary structure and chemistry play crucial roles in determining atomic diffusion, grain growth, and mechanical behavior in magnesium aluminate spinel (MgAl2O4, spinel). The grain boundary structure and chemistry can be modified by doping with cations, such as Ca2+, to facilitate grain boundary segregation and tailor such properties. However, the nanoscale details of the segregation behavior of calcium and its mechanism, and hence the dopant behavior influence on the grain boundary mechanical properties, have not yet been clearly understood. In this study, the segregation behavior of Ca2+ in spinel was quantitatively analyzed by X-ray energy dispersive spectrometry (XEDS) and electron energy-loss spectrometry (EELS), and compared to undoped spinel. Composition profiles obtained from EELS spectrum-imaging datasets across grain boundaries showed calcium segregation at the boundary core correlated with magnesium depletion. Additionally, energy-loss near-edge structure (ELNES) analysis of the Mg–K edge indicated that changes in the bonding status of the Mg2+ sublattice occurred after Ca-doping. It is implied that Ca2+ cations replace Mg2+ at tetrahedral sites in spinel. The calcium enrichment at grain boundaries obtained through quantitative XEDS analysis was in the range of 0.1–0.9 atoms/nm2 (0.03—0.26 monolayers). Calcium segregation had no detrimental effect on the indentation fracture toughness estimated through microindentation. The fracture behavior remains unaltered compared to undoped spinel, presenting primarily transgranular cracking. These results suggest that magnesium replacement by calcium atoms at the grain boundary core occurred with no compromise on the fracture toughness or fracture behavior, allowing it to maintain similar mechanical integrity as undoped spinel. [ABSTRACT FROM AUTHOR]

In the current research, the rare earth‐doped magnesium aluminate (MgAl2O4:Eu3+) spinels were produced by the combustion synthesis method. The employment of thermodynamic calculations revealed that the combustion approach is a proper way to synthesize MgAl2O4:Eu3+ material by urea fuel, although this procedure was fulfilled at 500°C, the final temperature will be around 2030°C. The x‐ray and FT‐IR spectra confirmed the successful formation of spinels, while it was shown that the calcination procedure results in a significant increase of crystallinity. On the other hand, it was interestingly seen that the addition of large amounts of Eu3+dopant (10 wt%) suppresses the crystallinity. The MAUD calculations interestingly revealed that the increase of Eu3+ dopant from 1 to 10 wt% leads to the increase of MgO and Al2O3 impurities. The related microstructural evaluations revealed that the particle size of the synthesized powders is mostly less than 40 nm which shows the superiority of combustion synthesis over other commercial methods. Also, the broadening of XRD peaks confirmed the formation of nano‐sized powder. The photoluminescence (PL) characterizations showed that doping of MgAl2O4 with 7 wt% Eu3+ brings the most intensive emission properties at the wavelengths of 592 and 617 nm. [ABSTRACT FROM AUTHOR]

Ceramic protective coatings applied to metallic interconnects play a vital role in solid oxide cells (SOCs) preventing interconnect degradation. In this study, uniform, dense, and crack-free single-layer coatings of MnCo 2 O 4 , Mn 1.7 CuFe 0.3 O 4 , and dual-layer coatings of MnCo 2 O 4 /Mn 1.7 CuFe 0.3 O 4 spinel are deposited onto complex-shaped metallic interconnect using electrophoretic deposition (EPD) method. The porosity of sintered MnCo 2 O 4 and Mn 1.7 CuFe 0.3 O 4 coatings in reduction treatment (1000 °C for 2h in H 2), followed by subsequent oxidation treatment (900 °C for 2h in air) is approximately 50% less than that of these coatings sintered in oxidation treatment (900 °C for 4h in air). The results indicate that the thickness of the sintered MnCo 2 O 4 , Mn 1.7 CuFe 0.3 O 4 single-layer, and MnCo 2 O 4 /Mn 1.7 CuFe 0.3 O 4 dual-layer coatings in reduction + oxidation treatments is 46.2%, 28.2%, and 23.1% denser, respectively, compared to sintered in oxidation treatment. Raman spectroscopy and Energy Dispersive Spectroscopy (EDS) analysis showed that in sintered dual-layer coatings subjected to reduction treatment followed by a subsequent oxidation treatment, exhibit a much more efficient interdiffusion processes throughout the thickness of the coating yielding the formation of a mixed (Mn, Cu, Fe, Co) 3 O 4 spinel, comparing to dual-layer coatings undergoing only oxidation treatment. The dual-layer spinel coatings of MnCo 2 O 4 /Mn 1.7 CuFe 0.3 O 4 present promising candidate for protective coatings on metallic interconnects. • A uniform and crack-free coating applied onto complex-shaped interconnects using the EPD method. • MnCo 2 O 4 /Mn 1.7 CuFe 0.3 O 4 dual-layer coating is a promising candidate for protective coatings. • Dual-layer coating densification in reduction + oxidation is higher than oxidation treatments. • Dual-layer coating provides higher protection against Cr diffusion than single-layer coating. [ABSTRACT FROM AUTHOR]

In this study a comprehensive analysis of the influence of synthesis route of CuFe 2 O 4 spinel mixed oxides on their catalytic performance in the N 2 O decomposition was carried out. A co-precipitation technique allowed one to obtain the CuFe 2 O 4 spinel with a higher specific surface area and pore volume compared to the synthesis with the application of organic additives. This resulted in better catalytic performance of the CuFe 2 O 4 samples prepared by co-precipitation. The microwave activation step with the duration of 1 min during the co-precipitation synthesis led to the formation of the CuFe 2 O 4 spinel with a higher content of oxygen vacancies per 1 m2 in comparison with the sample obtained without the microwave activation. This fact caused a significantly higher specific activity of the CuFe 2 O 4 spinel synthesized with the application of 1 min microwave activation. The increase of the microwave treatment time led to the fast growth of the contents of the CuO and α-Fe 2 O 3 phases, which are less active in the N 2 O decomposition, resulting in the activity drop. [Display omitted] [ABSTRACT FROM AUTHOR]

The electrophoretic deposition of a mixture of copper-manganese spinel oxide matrix with perovskite oxide dispersion phase and subsequent two-step sintering was investigated as a means of obtaining a new spinel/perovskite composite coating for application in metallic interconnects for solid oxide cell (SOC) technologies. The effect of a number of factors was examined, including electrophoretic deposition parameters such as solvent type, time, voltage, and dispersant content as well as different heat treatment conditions on the quality of the matrix of the coating material. A solution of ethanol-acetone (25/75 v/v) and 2.0 g L−1 of iodine dispersant with a deposition time of 60 s and a voltage of 60 V provided the thickest, most uniform coating as deposited. SEM observations showed that a dense coating of Cu–Mn spinel was obtained after 8 h of reduction at 1000 °C followed by 6 h of oxidation at 850 °C. Selected preparation parameters were applied to deposit composite coatings with a Cu–Mn spinel matrix and the addition of LNF, LSC and LSCF perovskites. [Display omitted] • EOH25/75ACT was determined to be the most suitable mixture for the deposition. • Mass gain of the deposit generally correlates with particle mobility. • Reduction in Ar–10%H 2 at 1000 °C and re-synthesis in air at 850 °C is optimal. • Morphology of composite coatings depend on type of perovskite additive. [ABSTRACT FROM AUTHOR]

[Display omitted] Nonaqueous Li − O 2 battery (LOB) is considered one of the most promising energy storage system due to its ultrahigh theoretical specific capacity (3500 Wh kg−1). Introducing vacancies in CoMn 2 O 4 catalysts is regarded as an effective strategy to enhance the electrochemical performances of LOB. However, the relation between vacancy types in CoMn 2 O 4 and catalytic performances in the LOB remains ambiguous. Herein, ordered porous CoMn 2 O 4 with oxygen and metal vacancies is obtained via solvothermal reaction followed by temperature-controlled calcination using polystyrene spheres as templates. The increase in treatment temperature reduces the content of oxygen vacancies while increasing that of the metal vacancies. Notably, experimental results and theoretical calculations show that oxygen vacancies in CoMn 2 O 4 have a greater influence than metal vacancies in modulating the LiO 2 adsorption during the reaction processes and reducing the overpotential. CoMn 2 O 4 synthesized at 500 ℃ (CoMnO-500) with higher oxygen vacancies exhibits stronger adsorption onto the LiO 2 , facilitating the formation of film-like Li 2 O 2. Therefore, an LOB with the CoMnO-500 catalyst presents the lowest overpotential of 1.2 V and longest cycle lifespan of 286 cycles at a current density of 200 mA g−1. This study offers insights into the effect of CoMn 2 O 4 vacancies on the formation pathway of Li 2 O 2 discharge products. [ABSTRACT FROM AUTHOR]

In this work, Co0.5Zn0.5LaxFe2-xO4 (0.00 ≤ x ≤ 0.10) spinel ferrites were synthesized using the sol-gel auto-combustion method. X-ray diffraction (XRD) analysis and Rietveld refinement confirmed the presence of a cubic spinel structure. The crystallite size was estimated to be between 17.5 nm and 26.5 nm using Scherrer's method and 31.27 nm-54.52 nm using the Williamson-Hall (W-H) method. Lattice constants determined from XRD and Rietveld refinement ranged from (8.440 to 8.433 Å and 8.442 to 8.431 Å), respectively. Scanning electron microscopy (SEM) revealed a non-uniform distribution of morphology with a decrease in particle size. The bandgap values decreased from 2.0 eV to 1.68 eV with increasing rare earth (La3+) doping concentration. Fourier-transform infrared (FT-IR) spectroscopy confirmed the presence of functional groups and M-O vibrations. The dielectric constant and dielectric loss exhibited similar behavior across all samples. The maximum tan d value obtained at lower frequencies. Regarding magnetic behavior, there was a decrease in magnetization from 55.84 emu/g to 22.08 emu/g and an increase in coercivity from 25.63 Oe to 33.88 Oe with higher doping concentrations. Based on these results, these materials exhibit promising properties for applications in microwave and energy storage devices. [ABSTRACT FROM AUTHOR]

The slow bidirectional conversion and fast shuttling of lithium polysulfides (LiPSs) remain the main obstacles that inhibit the practical application of lithium sulfur batteries (LSBs). Here, by engineering the in‐spin state of spinel oxides, V doping‐induced hexagonal nanosheets (V‐Co3O4 NS) with intermediate spin state (IS, t2g5 eg1) can form stable bond order toward LiS* based on the ligand field theory and molecular orbital theory, thus effectively accelerating the sulfur conversion kinetics. Owing to these merits, the V‐Co3O4 NS modified separator base battery achieves a high areal capacity of 15.37 mAh cm−2 with sulfur loading of 15.4 mg cm−2, and it displays a low‐capacity attenuation of 0.015% each cycle at 3.0 C for 1900 cycles. [ABSTRACT FROM AUTHOR]

In this study, varying amounts of MnO2 up to 5 wt.% were added to magnesium aluminate spinel (MA) bodies using a solid‐state sintering method at 1200–1600°C. The effect of MnO2 addition on the phase composition, microstructure, distribution of elements, and ionic valence of MA was investigated via X‐ray diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy, respectively. The results showed that Mg2+ ions in MA crystals were replaced by Mn2+ ions, resulting in the formation of the (Mg1‐xMnx)Al2O4 solid solution. The distorted crystal structures promoted the sintering reactions, and the mechanical characteristics of MA were greatly improved by the solid solution strengthening process. When the additive amount of MnO2 was 5 wt.% and the sintered temperature reached at 1600°C, excess manganese ions hardly dissolved into the lattice of MA. And these ions were only distributed at the grain boundaries of MgAl2O4, forming a “barrier” that hindered the migration and diffusion of particles, thereby suppressing the sintering process and weakening the mechanical strength of MA. [ABSTRACT FROM AUTHOR]

Photocatalytic water-splitting hydrogen production is expected to be a solution of global energy and environmental issues. In this work, to identify multicomponent photocatalysts towards water splitting, a density functional theory computation screening is presented on 84 AB 2 O 4 normal spinel candidates. The thermodynamic stability, band gap and band edge are selected as performance description factors to excavate candidates. Most of the reported photocatalytic materials in the screened candidates are reproduced. Owing to their unique band gap and band edge position, two novel visible light responsive spinels, MnGa 2 O 4 and MnIn 2 O 4 , are highlighted as promising photocatalysts. And a detailed analysis of their electronic and optical properties is performed for suitability in photocatalytic applications. The results show that they possess superior charge mobility, lower carrier recombination rate, wider and stronger visible light absorption than that of anatase TiO 2. More interestingly, the behavior of d-electrons in normal spinels shows dominating effect on the photocatalytic performances. • Screening normal spinels with first-principle calculations for photocatalysis. • Thermodynamic and electronic properties of 84 AB 2 O 4 type normal spinels were studied. • Two novel visible light responsive spinels are proposed as promising photocatalysts. • The behavior of d-electrons in normal spinels dominates photocatalytic performances. [ABSTRACT FROM AUTHOR]

The study shows that the addition of gadolinium ions has a significant impact on the structure, morphology, and adsorption properties of Ni-Co spinel ferrite that was synthesized by the sol–gel auto-combustion method. The research also indicates that the higher the Gd content, the greater the increase in the lattice parameter, which suggests that Gd3+ ions uniformly replaced the octahedral Fe3+ ions. The morphology and chemical composition of Gd-doped Ni-Co ferrites have been studied using SEM and EDS. Gd adding to the NiCoFe matrix increases the BET surface area by 50% (from 48 to 72 m2/g) and promotes the formation of mesopores with an average radius from 3.9 to 4.9 nm. The pHPZC values of Gd-doped ferrites are in the range of 7.22–7.39, which means that the ferrite surface will acquire a positive charge at natural pH, so this will promote the adsorption of Congo red anionic dye through electrostatic interaction forces. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to explain the mechanism of CR adsorption on the Ni0.5Co0.5GdxFe2-xO4 adsorbent surface. The ionic-covalent parameter has been estimated to describe the surface acid–base properties. Overall, this study highlights the potential of Gd3+ doping as a promising approach for enhancing the adsorption properties of nickel–cobalt ferrites. [ABSTRACT FROM AUTHOR]

Spin state is often regarded as the crucial valve to release the reactivity of energy‐related catalysts, yet it is also challenging to precisely manipulate, especially for the active center ions occupied at the specific geometric sites. Herein, a π–π type orbital coupling of 3d (Co)‐2p (O)‐4f (Ce) was employed to regulate the spin state of octahedral cobalt sites (CoOh) in the composite of Co3O4/CeO2. More specifically, the equivalent high‐spin ratio of CoOh can reach to 54.7 % via tuning the CeO2 content, thereby triggering the average eg filling (1.094) close to the theoretical optimum value. The corresponding catalyst exhibits a superior water oxidation performance with an overpotential of 251 mV at 10 mA cm−2, rivaling most cobalt‐based oxides state‐of‐the‐art. The π–π type coupling corroborated by the matched energy levels between Ce t1u/t2u‐O and CoOh t2g‐O π type bond in the calculated crystal orbital Hamilton population and partial density of states profiles, stimulates a π‐donation between O 2p and π‐symmetric Ce 4fyz2 orbital, consequently facilitating the electrons hopping from t2g to eg orbital of CoOh. This work offers an in‐depth insight into understanding the 4f and 3d orbital coupling for spin state optimization in composite oxides. [ABSTRACT FROM AUTHOR]

Li-rich Mn-based layered oxides provide a compelling amalgamation of high theoretical capacity and cost-effectiveness, positioning them as prime contenders for next-generation lithium-ion battery cathodes. However, their vulnerability to surface instability gives rise to a host of challenges, notably severe capacity and voltage fading. Consequently, the surface modification of Li-rich Mn-based layered oxides emerges as a viable solution to tackle this issue. Nevertheless, current methods exhibit various drawbacks, encompassing time-intensive procedures, environmental unfriendliness, and challenges in scalability. Hence, we present a technique employing ultrafast high-temperature heating technology to dynamically reshape the chemistry and structure of the surface of individual single-crystal Li1.2Mn0.54Ni0.13Co0.13O2 cathode particles (LMLO) within a rapid 8-second timeframe. Structural analysis reveals the seamless integration of the spinel structure onto the surface, intricately linked to the internal layered structure, accompanied by a notable abundance of oxygen vacancies. Leveraging the distinctive features of this modified structure, the material demonstrates enhanced discharge capacity, superior rate performance, and prolonged cycling stability compared to the unmodified counterpart. Significantly, in stark contrast to alternative preparation methods, this technique accomplishes the formation of the protective layer within a mere 8 seconds, showcasing unparalleled efficiency. Furthermore, it boasts safety and environmental friendliness, necessitates basic instrumentation, boasts ease of operation, and is well-suited for large-scale adoption. Consequently, this method is positioned to drive the commercialization of Li-rich Mn-based layered oxide cathode materials. [ABSTRACT FROM AUTHOR]

The reconstructed surface structure of Co‐based spinel oxides serves as the active site for oxygen evolution reaction (OER). However, the structural complexity of spinel oxides and surface dynamics during the OER hinder the understanding of the reconstruction mechanism and electronic structure of the active site. In this study, spinel Co3O4@(CoFeV)3O4 nanocube (CoFeV) is reported, a (001) facet‐defined spinel oxide comprising Co, Fe, and V deposited on the Co3O4 nanocube template to exclude facet‐dependent factors. Introducing highly dissoluble V cations accelerates the reconstruction process to enhance the electrocatalytic activity. CoFeV exhibited enhanced electrocatalytic activity (266 mV at 10 mA cm−2 in 1 M KOH) and durability (maintained stable electrocatalytic activity during a 200 h chronopotentiometry (CP) test at 100 mA cm−2) with significantly enlarged electrochemically active surface area (ECSA). The experimental and theoretical results demonstrated that V dissolution during catalysis induced oxygen vacancies, accelerating the surface reconstruction to highly active oxyhydroxide. Consequently, the anion exchange membrane water electrolyzer (AEMWE) of CoFeV as the anode exhibited a remarkable performance of 6.19 A cm−2 at 2.0 Vcell in 1 M KOH and robust durability for 96 h at a constant current density of 500 mA cm−2. [ABSTRACT FROM AUTHOR]

Achieving continuous tunability, high efficiency, and outstanding thermal stability of near‐infrared (NIR) phosphors remains challenging for optoelectronic device fields. To address this issue, a strategy is proposed based on the substitution of both cations and anions in the intermediate spinel structure, which successfully achieved fine‐tuning of NIR emission of Mg1+yGa2‐yO4‐yFy:Fe3+ phosphors with prominent optical characteristics. The NIR emission contains new luminescent centers with random O/F coordination and is successfully constructed. This co‐substitution promotes further inversion of the cationic sites and induces atomic disorder, changing the crystal coordination environment and making Fe3+ breakthrough the Laporte selection rule, enabling fine‐tuning of Fe3+ emissions in the range of 707–740 nm and broadening of the full width at half maximum by 30 nm. Moreover, the Mg1.15Ga1.85O3.85F0.15:Fe3+ phosphor reached a high quantum yield of 71.6% and presented excellent thermal stability with an emission intensity retention of 81% at 493 K. The emission of the fabricated NIR phosphor‐converted light‐emitting diodes also matched well with the photosensitive pigment Pfr, demonstrating its feasibility for plant growth lighting applications. [ABSTRACT FROM AUTHOR]

Although Ru‐based materials are among the outstanding catalysts for the oxygen evolution reaction (OER), the instability issue still haunts them and impedes the widespread application. The instability of Ru‐based OER catalysts is generally ascribed to the formation of soluble species through the over‐oxidation of Ru and structural decomposition caused by involvement of lattice oxygen. Herein, an effective strategy of selectively activating the lattice oxygen around Ru site is proposed to improve the OER activity and stability. Our synthesized spinel‐type electrocatalyst of Ru and Zn co‐doped Co3O4 showed an ultralow overpotential of 172 mV at 10 mA cm−2 and a long‐term stability reaching to 100 hours at 10 mA cm−2 for alkaline OER. The experimental results and theoretical simulations demonstrated that the lattice oxygen site jointly connected with the octahedral Ru and tetrahedral Zn atoms became more active than other oxygen sites near Ru atom, which further lowered the reaction energy barriers and avoided generating excessive oxygen vacancies to enhance the structural stability of Ru sites. The findings hope to provide a new perspective to improve the catalytic activity of Ru‐incorporated OER catalysts and the stability of lattice‐oxygen‐mediated mechanism. [ABSTRACT FROM AUTHOR]

The Jahn–Teller effect (JTE) arising from lattice–electron coupling is a fascinating phenomenon that profoundly affects important physical properties in a number of transition-metal compounds. Controlling JT distortions and their corresponding electronic structures is highly desirable to tailor the functionalities of materials. Here, we propose a local coordinate strategy to regulate the JTE through quantifying occupancy in the |${{d}_{{{z}^2}}}$| and |${{d}_{{{x}^2} - {{y}^2}}}$| orbitals of Mn and scrutinizing the symmetries of the ligand oxygen atoms in MnO6 octahedra in LiMn2O4 and Li0.5Mn2O4. The effectiveness of such a strategy has been demonstrated by constructing P2-type NaLi x Mn1–x O2 oxides with different Li/Mn ordering schemes. In addition, this strategy is also tenable for most 3d transition-metal compounds in spinel and perovskite frameworks, indicating the universality of local coordinate strategy and the tunability of the lattice–orbital coupling in transition-metal oxides. This work demonstrates a useful strategy to regulate JT distortion and provides useful guidelines for future design of functional materials with specific physical properties. [ABSTRACT FROM AUTHOR]

This paper has successfully employed a hydrothermal method to synthesize spinel LiMn1.5Ni0.5O4 (LMNO) cathode materials. Calcination at 600, 700, and 800 °C is performed to evaluate microstructure properties compared to as-prepared LMNO. The samples are investigated by XRD, SEM, TGA, FTIR. The crystallite sizes are smaller than the particle size of LMNO, revealing their polycrystalline nature. The TGA analysis supports the structural changes after calcined as revealed by XRD spectra. The FTIR spectrum indicates that the LMNO disorder-order transition occurs within the investigated temperature range. The peak broadening is attributable to the contribution of crystallite size and lattice strain, further analyzed according to Scherrer, Williamson-Hall, Size-Strain plot, and Halder-Wagner methods. Additionally, the results gained from different analysis methods are contrasted and discussed, which is the primary focus of this study. Generally, all analysis models indicate that the crystallite grows monotonously larger as temperature increases. The lowest lattice strain is observed in the as-prepared LMNO. However, calcining at 600 °C exhibits the highest developed lattice strain and gradually decreases as temperature increases further. This study also highlights the importance of convolution of size and strain contributions in determining the suitable method for calculating crystallite size and lattice strain. [ABSTRACT FROM AUTHOR]

Corrosion of the molten salts Na2SO4 and NaCl has become one of the major factors in the failure of steel components in boilers and engines. In this study, CoNiCrAlY cobalt-based cladding layers with different NiCr-Cr3C2 ratios were prepared by microbeam plasma cladding technology. The influence of the NiCr-Cr3C2 content on the microstructure, mechanical properties, and molten salt corrosion resistance of CoNiCrAlY was investigated. The CoNiCrAlY with a 25 wt.% NiCr-Cr3C2 (NC25) cladding layer possessed the highest microhardness (348.2 HV0.3) and the smallest coefficient of friction (0.4751), exhibiting great overall mechanical properties. The generation of protective oxides Cr2O3, Al2O3, and spinel phase (Ni,Co)Cr2O4 is promoted by the addition of 25 wt.% NiCr-Cr3C2, which significantly reduces the corrosion of the cladding layer, and this effect is much more obvious at 950 °C than that at 750 °C. Furthermore, its corrosion mechanism was clarified. From the findings emerge a viable solution for the design and development of new high-temperature corrosion-resistant coatings. [ABSTRACT FROM AUTHOR]

The spinel cathode LiMn1.5Ni0.5O4 (LMN) is garnering significant interest in the realm of lithium-ion batteries owing to its economical nature, elevated operating voltage, high theoretical energy density, and commendable thermal stability at a charged state. Various doping elements have been suggested to enhance the discharge capacity and prolong the lifetime of the LMN cathode. In this study, three doping elements (cobalt, aluminum, and magnesium) are investigated and compared using different characterization techniques. All three elements proved to be effective in extending the cycle life. Among all three elements, cobalt exhibits the highest threshold for dopant concentration beyond which performance degradation initiates. The cathode material with the highest performance, LiMn1.5Ni0.4Co0.1O4, is projected to have a cycle life of 900 cycles, contrasting with the 500 cycles of the undoped sample. [ABSTRACT FROM AUTHOR]

High‐quality magnesium aluminate spinel (MAS) transparent ceramics were successfully fabricated using Y3Al5O12 (YAG) as the sintering additive. The influence of the YAG content on the sintering behavior, microstructure, and optical properties of the MAS transparent ceramics was systematically investigated. A 4 mm‐thick sample with 0.01 wt.% YAG hot isostatic pressed at 1600°C achieved the highest in‐line transmittance of 84.0% at 400 nm and the flexural strength of the sample was as high as 347.3 MPa, which represents the highest‐performing reported MAS transparent ceramics that were sintered with oxide additives. [ABSTRACT FROM AUTHOR]

To understand the effect of the interactions between Ce‐treated steel and refractory on steel cleanliness, the high‐temperature reaction behaviors of Ce‐treated Al‐killed steel with different refractories (MgO, Al2O3, MgO⋅Al2O3, and CeO2) are investigated in laboratory at different times (30–90 min), and the inclusions in steel and the total oxygen contents of the steel are also analyzed. The results show that when the MgO refractory contacts with conventional Al‐killed steel grades, MgO‐Al2O3 spinel is generated as the reacted layer at the boundary; while it reacts with Ce‐treated steel, MgO–Al2O3 spinel is also formed, but it further transforms into Ce2O2S and CeAlO3 with time. In the Ce‐treated steel, CeAlO3 is proved as the stable phase; thus, the reacted layer of CeAlO3 can also be detected at the edges of Al2O3, MgO⋅Al2O3, and CeO2 refractories. Ce treatment leads to more serious degradation of refractory, and the thickness of the reacted layers at the steel–refractory boundary decreases with time due to the spalling of the layer, resulting in the formation of many CeAlO3 macroinclusions in steel and the rise of total oxygen contents of the steel. [ABSTRACT FROM AUTHOR]

The effect of varying amounts (1.0–5.0 wt %) of TiO 2 as an additive on the interfacial behavior between the MgAl 2 O 4 crucible materials and molten K417G superalloys during the vacuum induction melting has been characterized. Experimental results indicate that the phases of the TiO 2 -doped MgAl 2 O 4 materials were identified as MgAl 2 O 4 and minor amounts of MgTiO 3 after sintering at 1680°C for 1 h. When the TiO 2 -doped MgAl 2 O 4 crucibles were in contact with K417G melt, a reaction layer of MgTiO 3 was formed at the inner wall of the crucible. Moreover, some Al3+ and O2- were expelled toward the alloy side from MgTiO 3 near the interface to form Al 2 O 3 phases, and even form a continuous aluminum oxide layer in the 5 wt %TiO 2 -doped crucible after the melting experiment. Furthermore, only MC carbide with MgAl 2 O 4 as the core (MgAl 2 O 4 -(Ti, Mo)C hybrid-type) in the K417G alloy after the melting experiment can be observed, indicating that physical erosion predominates. [ABSTRACT FROM AUTHOR]

Blue, green, and khaki spinels were produced by self-propagating high-temperature synthesis (SHS) using Co 3 O 4 –ZnO–Mg(NO 3) 2 ·6H 2 O–Al(OH) 3 –Al, Ni 2 O 3 –ZnO–Cr 2 O 3 –Al(OH) 3 –Al, and Co 2 O 3 –Fe 2 O 3 –Al(OH) 3 –Al mixtures. The composition of the synthesis products was characterized by X-ray diffraction and IR spectroscopy. The oxides Co 3 O 4 , Co 2 O 3 , ZnO, Ni 2 O 3 , Cr 2 O 3 , Fe 2 O 3 , and aluminum hydroxide Al(OH) 3 were used for the synthesis. Fuel was provided by aluminum powder (ASD-4). The spinel-type ceramic pigments were synthesized using layer-by-layer combustion, which involves two parallel exothermic reactions: aluminum oxidation and aluminothermic reactions. The fast self-propagating reactions and high synthesis temperatures rapidly destroy the structure of Al(OH) 3 hydroxide in the starting mixture, producing gaseous reaction products that prevent the sintering of the spinels. The surface morphology of pigment powders and their composition was studied using a Quanta 3D 200i, FEI Co. scanning electron microscope and a Philips SEM 515 scanning electron microscope equipped with a local energy dispersive X-ray analysis (EDAX). The particle size of the synthesized spinels was approximately 1–5 μm. Colored spinels powders obtained by the SHS process can be used as ceramic pigments. [ABSTRACT FROM AUTHOR]

Local structure and magnetic properties of CoMn2O4 nanoparticles prepared by co-precipitation method have been examined. X-ray diffraction pattern shows mixed phase of tetragonal and cubic phases at room temperature with crystallite size of 42 nm, while Fourier transform infrared spectrum shows bands corresponding to tetrahedral and octahedral sites of spinel. Pre-edge feature from XANES and Fourier transform (FT) EXAFS spectra at Co and Mn K-edges confirm that majority of Co and Mn occupy A and B sites, respectively, while small amount of Co and Mn occupies the B and A sites, respectively. The spin dynamics of these nanoparticles show the dispersion of ac susceptibility (χ″) with frequency, and confirm the spin-glass like behaviour. Surprisingly, we observe a progressive increase in vertical magnetization shift (VMS), while measuring magnetization under field-cooled condition. Remarkably, a maximum VMS of 2.45 emu g−1 and exchange bias (EB) of 888.5 Oe were observed under a 10,000 Oe cooling field. Such a shift is intricately linked to the Yafet–Kittel spin structure of Mn3+ localized in B site and the EB could be due to the interaction between ferrimagnetic and spin-glass like phase. [ABSTRACT FROM AUTHOR]

Spinel oxides are a type of material that can be used in a wide range of applications, such as photocatalysis, hydrogen production and environmental protection. In this respect, calcium aluminate (CaAl2O4) and chromate (CaCr2O4) spinels were synthesized in this study by the coprecipitation method using potash solution as a precipitant. CaAl2O4 and CaCr2O4 spinels were annealed at 900 and 1100°C, respectively, for different periods. The obtained spinels were first characterized by thermal analysis, and the phase composition of the oxides was analysed using X-ray diffraction. Hydroxyl groups and absorbed water in the obtained precipitates disappeared after calcination and were observed via Fourier transform infrared spectroscopy. BET and SEM/EDS analyses were also used to determine the total surface area of the powder particles, the size of the grains and the morphology of the powders of the synthesized nanoparticles, respectively. The structural and morphological analyses revealed the formation of single-phase CaAl2O4 and dual-phase CaCr2O4, with specific surfaces for each spinel of 44.2165 and 5.7190 m2 g−1, respectively. Moreover, DFT calculations were performed on the materials, and the direct bandgaps of these spinels were found to be 4.365 eV for CaAl2O4 and 2.256 eV for CaCr2O4. The results indicated that different compositions led to different optical bandgaps. Finally, the results indicate that due to the suitable characteristics and properties of the produced spinel oxides, they are among the promising materials that may be employed as semiconductors for various applications. [ABSTRACT FROM AUTHOR]

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Copyright of Nonferrous Metals (Extractive Metallurgy) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Advanced oxidation technology based on PeroxyMonoSulfate (PMS) has become a research hotspot in the field of water treatment. To improve the activation efficiency of PMS, electrochemically assisted spinel type catalyst CoFe2O4 was used to activate PMS and achieve effective degradation of acetaminophen. The influence of single factor on degradation was explored to determine the best degradation process parameters of E/CoFe2O4/PMS system. Results show that under the optimum reaction conditions (DC voltage is 6V, the initial mass concentration of acetaminophen is 10mgL−1, the dosage of CoFe2O4 is 0.3gL−1, and the mass concentration of PMS is 1.5gL−1), the degradation rate of acetaminophen reaches up to 95% within 20min. CoFe2O4 catalyst showed a good stability, with only a 12% decrease in acetaminophen degradation after three cycles. Radical quenching tests show that ⋅OH and SO4−⋅ played predominant roles in the advanced oxidation process. This work provides a new strategy for more efficiency in PMS activation. [ABSTRACT FROM AUTHOR]

Worldwide environmental challenges pose critical problems with the growth of the global economy. Addressing these issues requires the development of an eco-friendly and sustainable catalyst for degrading organic dye pollutants. In this study, copper-doped magnesium aluminates (CuxMg1−xAl2O4) with x = 0.0–0.8 were synthesized using a citrate-based combustion route. The inclusion of Cu(II) significantly impacted the structural, microstructural, optical, and photocatalytic activity of the catalyst. Rietveld analysis of X-ray diffraction powder profiles revealed single-phase spinels crystallized in the face-centered cubic unit cell with Fd 3 ¯ m space group. Chemical states of the ions, surface morphology, and elemental investigation were analyzed by X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. UV–visible and diffuse reflectance spectroscopies confirmed the reduction of the band gap due to Cu(II) doping, validated by first-principle investigations using the WIEN2k code. The catalyst with x = 0.8 showed higher photocatalytic efficacy (90% and 93%) for removing two azo organic dye pollutants, rhodamine B and methyl orange, respectively, within 120 min. Degradation kinetics followed a pseudo-first-order mechanism. The doped (0.8) sample was structurally and morphologically stable and reusable under visible irradiation, retaining performance after three runs. Scavenger studies confirmed hydroxyl and superoxide radicals' involvement in the degradation. This work presents an effective approach to enhancing CuxMg1−xAl2O4 catalysts' photodegradation performance, with potential applications in pharmaceuticals and wastewater remediation. [ABSTRACT FROM AUTHOR]

Corrosion of steel is an issue that cannot be ignored in contemporary society. Due to large-scale corrosion, it is urgent to develop a surface treatment process that enhances the corrosion resistance of steel, allowing for application in various scenarios as needed. This study aims to investigate a novel surface treatment process to extend the service life of corroded Q235 steel, reduce its sensitivity to corrosion, and enable its use in multiple environments. This study employs the sol-gel method, using manganese nitrate solutions of varying concentrations to treat the surface of Q235 steel after different electrolysis times. The optimal conditions for precursor preparation were found to be a Mn2+ concentration of 0.1 mol/L and an electrolysis time of 2 h. Electrochemical tests using NaCl solutions of different concentrations revealed a significant reduction in the corrosion current for the composite coating based on Q235 steel treated with this method in NaCl solutions with wt.% = 1, 2, 3, 4, 5. Furthermore, the resistance to corrosion was strongest in the NaCl solution with a concentration of 1 wt.% where the corrosion current decreased from 24.8 µA/cm2 to 6.79 µA/cm2. Additionally, the coating was found to be diffusion-controlled in the early stages of the corrosion process and charge transfer-controlled in the later stages. The MnFe2O4 spinel coating demonstrated the greatest enhancement in corrosion resistance in the wt.% = 1 NaCl solution. [ABSTRACT FROM AUTHOR]