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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]

The chemical solution-deposited zinc ferrite (ZFO; ZnFe2O4) RRAM devices on Pt/Ti/SiO2/Si substrate are being reported. Fabricated devices show the positive as well as negative unipolar switching memory properties. Thickness of ZFO thin films in Au/ZFO/Pt structure was varied to explore the resistive switching behavior. It is reported that forming voltage and resistance of the device increase by increasing the number of ZFO layers. Our results reveal that ZFO thin film deposited by eight times spin coating with a thickness of eight layers illustrates stable resistive switching with the most steady Set (2 V) and Reset voltages (0.5 V) as compared to the devices with two, four, and six layers. It also demonstrates the enhanced endurance of greater than 300 switching cycles and stable time-dependent resistance greater than 104 s. The current transport mechanism is Ohmic at low-resistance state, while it leads to Schottky emission at high-resistance state. The possible switching mechanism is also discussed for the possible application of ZFO-based memory for nonvolatile RRAM devices. [ABSTRACT FROM AUTHOR]

The chemical solution-deposited zinc ferrite (ZFO; ZnFe2O4) RRAM devices on Pt/Ti/SiO2/Si substrate are being reported. Fabricated devices show the positive as well as negative unipolar switching memory properties. Thickness of ZFO thin films in Au/ZFO/Pt structure was varied to explore the resistive switching behavior. It is reported that forming voltage and resistance of the device increase by increasing the number of ZFO layers. Our results reveal that ZFO thin film deposited by eight times spin coating with a thickness of eight layers illustrates stable resistive switching with the most steady Set (2 V) and Reset voltages (0.5 V) as compared to the devices with two, four, and six layers. It also demonstrates the enhanced endurance of greater than 300 switching cycles and stable time-dependent resistance greater than 104 s. The current transport mechanism is Ohmic at low-resistance state, while it leads to Schottky emission at high-resistance state. The possible switching mechanism is also discussed for the possible application of ZFO-based memory for nonvolatile RRAM devices. [ABSTRACT FROM AUTHOR]

CO 2 serves as a crucial precursor for synthesizing aromatic, offering a resultful pathway for utilizing non-petroleum carbon sources. Nonetheless, the Anderson-Schulze-Flory (ASF) distribution limits aromatics selectivity, challenging the direct conversion of CO 2 into specific aromatic products. Bifunctional catalysts consisting of ZnCr 2 O 4 , ZnAl 2 O 4 and ZnIn 2 O 4 spinel with nano-flake ZSM-11 zeolite were constructed and investigated for converting CO 2 to valuable aromatics. Remarkably, the selectivity towards aromatics greatly surpasses the constraints of ASF. Under identical reaction conditions, the single pass CO 2 conversion of the ZnCr 2 O 4 /ZSM-11 increased by 7.2% and 5.2%, while the aromatic selectivity rose by 9.5% and 10.5%, respectively, compared to the ZnAl 2 O 4 /ZSM-11 and ZnIn 2 O 4 /ZSM-11. Additionally, under optimal conditions (300 °C, 3.5 MPa and a gas hourly space velocity (GHSV) of 1800 mL·g cat −1·h−1), ZnCr 2 O 4 /ZSM-11 displayed outstanding aromatic selectivity of 90.5% (without CO) alongside a single pass CO 2 conversion of 23.6%. Simultaneously, the synthetic ZSM-11 facilitates the timely diffusion of monocyclic aromatics and the production of C 8 –C 12 monocyclic aromatics, which constitute 97.2% of the total aromatic products, while polycyclic aromatics account for only 0.2%. Even after 100 h, the ZnCr 2 O 4 /ZSM-11 catalyst maintained its significant catalytic activity with CO 2 conversion and aromatic selectivity at 22.0% and 88.0%, respectively. These results highlight the potential of ZnCr 2 O 4 /ZSM-11 for directly converting CO 2 to valuable aromatics. [Display omitted] • ZnX 2 O 4 (X = Cr, In, Al) spinels were designed to compare the catalytic properties. • ZnCr 2 O 4 /ZSM-11 bifunctional catalyst enables direct CO 2 to aromatics conversion. • ZnCr 2 O 4 /ZSM-11 achieved 90.5% aromatics selectivity, 23.6% CO 2 conversion. • Remarkably, C 8 –C 12 monocyclic aromatics constitute 97.2% of the total aromatic. • Post 100 h, catalyst still gave 22.0% CO 2 conversion, 88.0% aromatics selectivity. [ABSTRACT FROM AUTHOR]

In this work, we report the thermoelectric behaviour of flexible fabric-based Mo doped CuAl 2 O 4. The doped Mo atom occupies the interstitial positions of the spinel lattice of CuAl 2 O 4. This results the lattice expansion and also provides the carrier electrons. Initially, the pristine CuAl 2 O 4 has the carrier concentration of 2.81 × 1014 cm−3, while doping with molybdenum, it not only increases the concentration of the carriers (about −7.65 × 1015 cm−3), but also changes the carrier type. The minimum doping (2 %) of molybdenum to spinel CuAl 2 O 4 (CuAl 2 O 4 Mo 0.02) creates the fermi level near to the conduction band, which reduces the band gap and results in the effective electrical conductivity as 0.69 Scm−1 at 340 K. The heavy doping enhances the scattering process. This leads to deduction of mobility and lower the electrical conductivity. The highest power factor of 0.0599 μWcm−1K−2 is achieved for the CuAl 2 O 4 Mo 0.06 sample at 300 K. This is due to the high Seebeck coefficient value of the sample and has an ultralow thermal conductivity value of 0.056 W/mK. The highest output voltage of 3.9 mV is achieved for parallelly connected p-type CuAl 2 O 4 -n-type CuAl 2 O 4 Mo 0.02 thermoelectric device at the temperature difference of ΔT = 4.1 K. This research findings justify, the doping of molybdenum in the spinel lattice effectively enhances the thermoelectric properties of CuAl 2 O 4 and provide the new ideas for the flexible, wearable fabric based thermoelectric research. [Display omitted] [ABSTRACT FROM AUTHOR]

Recent advancements in high entropy oxides (HEOs) have sparked significant interest as a promising frontier in materials research, revolutionizing the landscape of material design and properties. They exhibit outstanding stability, intriguing functional properties, and unparalleled design flexibility enabled by the inclusion of multiple cations in these materials. In this study, we successfully stabilized several new high entropy spinel oxides with compositions (Ni 0.2 (Mg/Mn) 0.2 Co 0.2 Cu 0.2 Zn 0.2)B 2 O 4 (B = Al, Ga, Mn). The room temperature X-ray diffraction (RT-XRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectroscopy (EDS) measurements highlight the crystal structure of the materials with excellent chemical homogeneity at the micro-scale. RT-XRD and Raman spectroscopy confirmed the formation of single-phase cubic spinel structures. However, the Mn-based sample exhibited tetragonal distortion. Magnetic measurements show remarkable variation in the magnetic properties: (Ni 0.2 Mg 0.2 Co 0.2 Cu 0.2 Zn 0.2)Mn 2 O 4 shows complex ferrimagnetic behavior, Al and Ga based diamond lattice (Ni 0.2 Mg 0.2 Co 0.2 Cu 0.2 Zn 0.2)B 2 O 4 (B = Al and Ga) materials revealed extremely high magnetic frustration and absence of magnetic ordering down to 1.8 K, indicative of exotic frustrated state. Magnetic transitions (spin-glass like) are observed in (Ni 0.2 Mn 0.2 Co 0.2 Cu 0.2 Zn 0.2)B 2 O 4 (B = Al and Ga) materials. Our study highlights the potential to finely tune the magnetic responses through compositional engineering, thus paving the way for the development of tailored magnetic materials for various applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Stable inert anode presents a promising alternative to active graphite anodes in molten salt electrolysis, offering a significant reduction in CO 2 emissions. However, developing such anodes remains a significant challenge. In this study, a novel metal-spinel cermet inert anode for use in CaCl 2 -based molten salts was introduced. Three spinel materials—NiFe 2 O 4 , MgFe 2 O 4 , and MgAl 2 O 4 —were synthesized and their electrochemical properties were compared. It was observed that NiFe 2 O 4 emerged as the most effective spinel ceramic. Subsequently, 20 wt%(50Cu-Ni)- x NiO-NiFe 2 O 4 (x = 0, 10, 20) were prepared and evaluated. Furthermore, according to polarization behavior, density, and conductivity, the 20 wt%(50Cu-Ni)-10NiO-NiFe 2 O 4 anode exhibited superior performance in CaCl 2 -CaO molten salt, which outperformed conventional SnO 2 inert anodes. Its corrosion rate was measured at only 1.25 × 10−3 g cm−2 h−1 over 20 h of electrolysis. Additionally, carbon spheres were successfully prepared using the 20 wt%(50Cu-Ni)-10NiO-NiFe 2 O 4 cermet anode in CaCl 2 -5 wt% CaCO 3 molten salt, thereby achieving a current efficiency of ∼85.5 %. The NiFe 2 O 4 -based cermet exhibited significant potential as an inert anode for sustainable metallurgical processes. [ABSTRACT FROM AUTHOR]

Spinel saggar was prepared using Magnesium Aluminum spinel (MgAl 2 O 4), KF and TiO 2 as primary raw materials. The saggar's toughness was enhanced through in-situ generation of potassium titanate whisker (PTW). The impact of sintering temperature on the saggar's phase composition, whisker growth and physical properties was investigated. The findings indicated that the spinel saggar exhibited high densities and robust mechanical strength following heat treatment at 800 °C for 3 h, with an apparent porosity of 27.9 %. The cold modulus of rupture (CMOR) and cold crushing strength (CCS) were measured at 5.58 MPa and 21.05 MPa, respectively. The saggar retained rate 75.6 % of their strength after three thermal cycles at 800 °C for 20 min followed by air cooling. Corrosion analysis identified LiAlO 2 as the primary corrosion product of the spinel saggar. PTW facilitated particle bonding, enhancing the strength and toughness of the spinel saggar. This promoted the dispersion and absorption of thermal stresses during cyclic corrosion to prevent further damage. In contrast, for cordierite-mullite saggar corrosion products included LiAlO 2 , eucryptite(β-LiAlSiO 4) and Li 4 SiO 4. The disparate thermal expansion among these phases resulted in the formation of through cracks, exacerbating saggar corrosion damage. The spinel saggar demonstrated superior performance during the cyclic corrosion process. [ABSTRACT FROM AUTHOR]

Polycrystalline magnesium aluminate spinel (PMAS) ceramics is a kind of transparent oxide ceramic with the advantages of high hardness, high mechanical strength, thermal stability and chemical corrosion resistance. The optical transmittance and infrared absorption edge of PMAS ceramic are better than that of sapphire and ALON in the mid-infrared band with the wavelengths greater than 4.5 μm, which makes it as an ideal material for manufacturing the optics used in the fields of transparent armor protection, infrared optical window and infrared missile dome. However, the hardness of PMAS ceramics is close to that of sapphire, and the brittleness is greater than that of sapphire, which brings great challenges to ultra-precision ductile grinding. In this paper, the surface characteristics and damage mechanisms in ultra-precision grinding of PMAS ceramics were systematically researched based on AE signals monitoring. Firstly, the effects of grinding depth, feed speed and grain size on the surface characteristics were studied in detail. Secondly, the influences of grinding depth and feed speed on the damage characteristics of PMAS ceramics were researched based on energy spectrum analysis of AE signals. Thirdly, the evolution mechanisms of material removal modes and damage characteristics were revealed based on time-frequency analysis of AE signals. Then, the damage types on ductile surfaces and initiation mechanisms of damage crack were investigated. Ultimately, the crack-free ductile surfaces and surface roughness (Sa) of 3 nm were achieved through ultra-precision grinding. [ABSTRACT FROM AUTHOR]

Vacancy engineering presents an appealing method for modifying the electronic structure of spinel architectures. However, based on well-defined vacancy concentrations, how to design anionic vacancies to modulate electromagnetic parameters as well as electromagnetic wave absorption (EMA) properties is less studied. Here, NiCo 2 Se 4 spinel structures were prepared using different selenization methods, and the Se vacancy defect concentration was controlled by changing the annealing temperature, thus regulating the EMA properties. Among them, the design of the hollow structure effectively enhanced the EMA performance. Moreover, the increase of Se vacancy concentration increases the conductivity loss while regulating the electronic structure, and also acts as an unsaturated site to induce the formation of dipoles to optimize the polarization loss. The effective absorption bandwidth (EAB) of NiCo 2 Se 4 -130 reaches 8.48 GHz at 2.4 mm at the highest Se vacancy concentration. This work establishes a direct relationship between vacancy concentration and the electromagnetic wave dissipation capability, offering valuable insights for the development of advanced EMA materials. [ABSTRACT FROM AUTHOR]

The investigation focused on nanovoids (free-volume defects) in spinel MgAl2O4 ceramics, synthesized at various temperatures, both before and after saturation (water-immersion), utilizing the positron annihilation spectroscopy method. The findings were analyzed within the framework of a multi-channel model. It was demonstrated that this model integrates channels capturing positrons by volumetric defects and the decay of ortho-positronium atoms. Within this refined approach, the first component reflects the microstructural characteristics of the spinel structure, the second component corresponds to volumetric defects near grain boundaries, while the third pertains to the "pick-off" process of ortho-positronium annihilation within water-filled nanopores of the ceramics. [ABSTRACT FROM AUTHOR]

The electrophysical properties of nanostructured MgAl2O4 ceramics sintered at 1300 °C for 5 h, as well as thick films were obtained and investigated. The study of adsorption-desorption cycles was carried out after sintering and aging test. It is shown that ceramic has a sensitivity to humidity in the range of 25–95% with minimal hysteresis of the characteristic in adsorption-desorption cycles, which can be eliminated after the aging test. Thick films based on it are characterized by hysteresis and loss of sensitivity at low values of relative humidity, which is caused by the clogging of small nanopores. [ABSTRACT FROM AUTHOR]

High‐entropy oxides (HEOs), known for their excellent thermodynamic stability due to their high‐entropy effect. In this study, high‐entropy (NixAlCoCrMn)3O4 oxides of spinel structure were synthesized by sol‐gel method. This HEO has a self‐reconfiguration properties in the reaction, and its internal Ni and Co ions exsolve to form a uniformly dispersed NiCo alloy on the surface. The increase of Ni content promotes the exsolution of Ni and Co ions from the interior of the spinel. The high‐entropy with a large number of oxygen vacancies not only possesses a stable structure to limit the migration of NiCo alloys, but also enhances the hydrogen overflow. In the CO methanation reaction, it has 99 % CO conversion with 87 % methane selectivity within 400 °C, and it is stable in the long‐term test. This work provides a new idea for exploring the use of high‐entropy materials to improve thermal catalytic activity and stability. [ABSTRACT FROM AUTHOR]

The shape‐defined ZnFe2O4 spinel with cubic and octahedral morphology was hydrothermally synthesized, respectively, and used as catalyst precursor for Fischer–Tropsch synthesis (FTS). The structure of ZnFe2O4 spinel was changed to ZnO and Fe5C2 (Fe5C2/ZnO) after reduction and carbonization. Interestingly, ZnFe2O4 with cubic morphology exhibited much higher catalytic activity and selectivity toward low‐carbon olefins (C2–C4) than the octahedral one under identical conditions, and the latter tended to produce the saturated alkanes. The primary properties of ZnFe2O4 materials before and after reduction were systematically studied through a series of characteristic technologies to reveal the difference in catalytic performance between the two ZnFe2O4 spinels with different morphologies. [ABSTRACT FROM AUTHOR]

MgO-Al 2 O 3 -SiO 2 -ZnO-TiO 2 -ZrO 2 glass with the addition of 8 mol% Na 2 O as flux has been prepared by the melt-casting method, and transparent glass-ceramics (GCs) with spinel (MgAl 2 O 4 and ZnAl 2 O 4) as the main crystalline phases were prepared by controlled crystallization. The optimum nucleation temperature was determined through DSC method, which is conducted on the glass with different preheating temperatures. The type and size of crystals in MAS glass-ceramics are highly dependent on the heat treatment. As the nucleation time increased to over 25 h, the formation of spinel was hindered due to the increasing formation of Na 2 TiSiO 5 in the glass, which consumed most of the Ti4+ ions during the long-term nucleation. When the nucleation time is up to 35 h, there is only Na 2 TiSiO 5 crystalline phase in the GCs. The nucleation time have a significant effect on the ion-exchange process through changing the crystals type and microstructure of GC. Both the Na + ions in Na 2 TiSiO 5 crystals and glassy phase can participate ion-exchange with K+ ions in molten salts, facilitating to form compressive stress. While, the formation of spinel consumed a lot of [AlO 4 ] in glassy phase, which decreasing the ion-exchange channel and thus hindering the ion-exchange. When heat treated at 700 °C/25 h + 830 °C/1 h, the MAS glass-ceramic showed transparency over 78 % at 550 nm, and its Vickers hardness reached ∼845 kgf/mm2 after ion-exchange. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of preparing quinary equimolar high-entropy oxides within the Co–Cu–Fe–Mg–Mn–Ni–O system was explored using the reactive flash sintering (RFS) technique. Various compositions were tested using this technique under atmosphere pressure, leading to the formation of two primary phases: rock-salt and spinel. Conversely, a new high-entropy oxide was produced as a single-phase material with the composition (Co 0.2 ,Cu 0.2 ,Mg 0.2 ,Mn 0.2 ,Ni 0.2)O when RFS experiments were conducted in nitrogen atmosphere. The reducing conditions achieved in nitrogen enabled the incorporation of cations with oxidation states different from +2 into the rock-salt lattice, emphasizing the critical role of the processing atmosphere, whether inert or oxidizing, in the formation of high-entropy oxides. The electrical characterization of this material was obtained via impedance spectroscopy, exhibiting a homogeneous response attributed to electronic conduction with a temperature dependence characteristic of disordered systems. [ABSTRACT FROM AUTHOR]

Features of high-temperature oxidation of N70VTYu-ID alloy with γ‑solid solution structure are studied. It is shown that characteristics describing this process stabilize with increasing oxidation time. The calculated oxidation activation energy is ~220,000 ± 5000 J/mol, which is comparable to the nickel self-diffusion activation energy. Influence of preliminary short-term high-temperature oxidation on alloy scale resistance is investigated. It is shown that this combined heat treatment can briefly increase N70VTYu-ID alloy scale resistance. [ABSTRACT FROM AUTHOR]

This investigation focused on the fabrication of ceramic ferrimagnetic CuFe2O4–conductive polypyrrole (PPy) composites for energy storage. CuFe2O4 with a crystal size of 20–30 nm and saturation magnetization of 31.4 emu g−1 was prepared by hydrothermal synthesis, and PPy was prepared by chemical polymerization. High-active-mass composite electrodes were fabricated for energy storage in supercapacitors for operation in a sodium sulfate electrolyte. The addition of PPy to CuFe2O4 resulted in a decrease in charge transfer resistance and an increase in capacitance in the range from 1.20 F cm−2 (31 F g−1) to 4.52 F cm−2 (117.4 F g−1) at a 1 mV s−1 sweep rate and from 1.17 F cm−2 (29.9 F g−1) to 4.60 F cm−2 (120.1 F g−1) at a 3 mA cm−2 current density. The composites showed higher capacitance than other magnetic ceramic composites of the same mass containing PPy in the same potential range and exhibited improved cyclic stability. The magnetic behavior of the composites was influenced by the magnetic properties of ferrimagnetic CuFe2O4 and paramagnetic PPy. The composites showed a valuable combination of capacitive and magnetic properties and enriched materials science of magnetic supercapacitors for novel applications based on magnetoelectric and magnetocapacitive properties. [ABSTRACT FROM AUTHOR]

The corrosion of slag on refractories usually starts from the matrix, so improving the slag resistance of the matrix is of great significance for the slag resistance of the refractories. To clarify the influence of matrix on the slag resistance of magnesia–carbon refractories, the slag corrosion experiments were conducted at 1873 K on MgO–C refractories, low‐carbon MgO–C refractories, and MgO–SiC–C refractories. The results showed that the slag resistance of MgO–C refractories was higher than that of low‐carbon MgO–C refractories, and the slag resistance of MgO–SiC–C refractories was superior to that of low‐carbon MgO–C refractories. The interaction between MgO–SiC–C refractories and slag generated high melting point phases such as forsterite and spinel, reducing the routes for the slag to infiltrate the inside of the refractories. MgO–SiC–C refractories reacted with slag to increase the viscosity of the slag, the viscosity being 86.3% and 51.9% higher than in the case of low‐carbon MgO–C and MgO–C refractories, respectively. Compared with MgO–SiC–C refractories, MgO–C refractories did not exhibit overwhelming advantages in slag resistance. Due to the low‐carbon content and good slag resistance, MgO–SiC–C refractories were promising low‐carbon magnesia‐based refractories for high‐temperature industries. [ABSTRACT FROM AUTHOR]

Yttrium aluminum garnet (YAG) powders, synthesized through a partial wet chemical process, exhibit controlled morphology, high phase purity, and uniform homogeneity etc. This process involves the precipitation of aluminum ions onto Y 2 O 3 particles. The transformation process of the Al-compound/Y 2 O 3 precursor structure leads to the direct crystallization of pure YAG at 900 °C, passing through an intermediate stage where hexagonal YAH phase forms. A comprehensive study was conducted on the impact of preformed YAG as a reinforcing phase on the densification, mechanical, and thermo-mechanical properties of MgAl 2 O 4 -YAG composite, sintered under pressureless sintering in temperature range of 1500 °C–1600 °C. The inclusion of YAG particulate up to 5.0 wt% significantly enhances the densification, hardness, fracture toughness, flexural strength and high-temperature mechanical behavior of magnesium aluminate spinel (MAS) ceramics, however, increasing the YAG content beyond 5.0 wt% causes a reduction in these properties. The optimized addition of YAG particulate contributes to reducing the average grain size and refining the microstructure of the spinel ceramic matrix. [ABSTRACT FROM AUTHOR]

Electronic configuration regulation is usually a feasible strategy to boost the electrocatalytic performance for transition metal oxides. Herein, a simple high-temperature annealing method is employed to optimize the electrocatalytic activity towards hydrogen evolution reaction (HER) for spinel oxide Co 3 O 4. The experimental results indicate the simple thermal treatment partially drives the structure reversal in spinel Co 3 O 4 , and it induces the redistribution of cobalt ions at tetrahedral and octahedral sites. Thereby, the electronic configuration regulation occurs, and the e g occupation of cobalt ions at octahedral sites increases up to 1, optimizing the HER reaction kinetics. The sample treated at 900 °C exhibits the highest activity, with overpotential of 335 mV at current density of 10 mA cm−2, and Tafel slope value of 99.3 mV dec−1. This work offers a new way of tuning the electronic configuration in spinel oxides to boost HER electrocatalytic activity. • A simple high-temperature annealing method was adopted to partially drive the structure reversal in Co 3 O 4. • Partial structure reversal can induce redistribution of cobalt ions, and effectively modulate electronic configuration. • Complex spinel exhibited better HER activity than that of normal spinel. [ABSTRACT FROM AUTHOR]

A novel method to prepare high-quality enstatite-spinel based glass-ceramics by co-utilization of ferronickel slag (FNS) and iron ore tailings (IOT) via microwave-assisted one-step crystallization was proposed with an emphasis on the effect of IOT content on the preparation process. The thermodynamic analysis demonstrated that incorporating appropriate amounts of IOT into FNS can effectively transform olivine in FNS into enstatite. The experimental exploration revealed that the crystallization activation energy of the parent glass decreased from 564.6 kJ/mol to 351.93 kJ/mol when the IOT content increased from 30 wt% to 45 wt%. Meanwhile, the Avrami index of the parent glass increased from 3.88 to 4.81, indicating less depolymerization. In the subsequent crystallization process, with increasing content of IOT, the main phase was enstatite, accompanied by small amounts of spinel which acted as nucleation sites promoting the enstatite formation. Due to the decreased depolymerization degree that resulted in fewer nucleation sites, the average grain size of enstatite increased from 123 nm to 196 nm. By controlling crystallization of the melted mixture of 65 wt% FNS and 35 wt% IOT at 863 °C for 20 min, the resulting enstatite-spinel based glass-ceramics had excellent comprehensive properties, namely density of 3.13 g/cm3, bending strength of 153.53 MPa, Vickers microhardness of 9.22 GPa, acid resistance of 99.89%, and alkali resistance of 99.72%. With a much shorter crystallization time (1/6 of conventional one), the product obtained by microwave-assisted one-step crystallization had properties comparable to those derived from similar wastes. [Display omitted] [ABSTRACT FROM AUTHOR]

Excellent properties are required for refractories used for secondary refining because of the harsh service conditions. The current study investigated the effect of calcium boride (CaB 6) on the properties of magnesium oxide (MgO)‒based refractories. The sample with 0.4 wt% CaB 6 exhibited excellent properties. It possessed the highest bulk density indicating that a suitable content of CaB 6 can increase the compactness of the refractories. The in-situ formation of aluminum oxycarbonitride (Al 3 CON) at high temperatures in the MgO-based refractories was from the reaction of Al, Al 4 C 3 , AlN, and Al 2 O 3 due to the addition of Al powders, which endowed them with high strength. The refractory containing 0.4 wt% CaB 6 also exhibited the highest hot modulus of rupture (HMOR) of 26.6 MPa, which was around 2.5 times the strength of commercial MgO‒CaO bricks and 1.5 times that of the samples without CaB 6 addition. In addition, it exhibited the best oxidation resistance revealed by the minimum thickness of the decarbonization zone, because the addition of CaB 6 promoted the formation of a dense magnesium aluminate spinel (MgAl 2 O 4 , MA) layer between the oxidized and non-decarburized zone in the refractories, thereby promoting the resistance of the samples to oxidation. It also exhibited excellent thermal shock resistance, and the residual strength ratio reached 76.6 %. The corrosion depth of the sample containing 0.4 wt% CaB 6 was 9.8 % that of the MgO‒CaO bricks. This work indicates a potential alternative for producing high‒performance resin‒bonded MgO-based refractories with CaB 6 in secondary refining furnaces. [ABSTRACT FROM AUTHOR]

The Si‐based self‐powered broadband photodiode (SSBP) is prized for its ability to swiftly detect light across a wide spectrum without requiring an external voltage. However, boosting its efficiency remains challenging due to its high refractive index and limited UV light penetration. A combination of Si with ZnGa2O4, an ultra‐wide‐bandgap spinel material, can bring new opportunities to address these shortcomings of SSBP. In this study, a ZnGa2O4/p‐Si heterojunction photodiode is presented, which is capable of detecting UV to near‐infrared light autonomously. Operating without bias, this device exhibits excellent rectification and detects wavelengths from 265 to 1000 nm, achieving impressive performance metrics such as a photo‐to‐dark current ratio of 5.8 × 104, response speed of less than 3 ms, responsivity of 117 mA W−1, and specific detectivity of 5.5 × 1012 Jones while the photodiode demonstrates exceptional stability and durability under harsh conditions. The versatility of this device is demonstrated by applying it to the optical imaging sensors and physically unclonable security devices. This study provides new inspirations for the development of the energy‐efficient and emerging optical sensing technologies. [ABSTRACT FROM AUTHOR]

The electrolytic cell is the main equipment for electrolytic aluminum production. The visual electrolytic cell can observe and study the production process and mechanism of aluminum electrolysis. The effects of Y2O3 addition and sample thickness on the densification behavior and transmittance of Magnesium-aluminate spinel (MAS) were studied. The relative density, porosity, phase composition, microstructure, Vickers hardness, and transmittance of the sintered samples were characterized using the Archimedes method, x-ray diffraction analysis, scanning electron microscopy, Vickers hardness tester, and UV-visible near-infrared diffuse reflection. The results show that the appropriate amount of Y2O3 can enhance the transmittance of MgAl2O4 and the optimum Y2O3 content is 2 wt.%. At this time, the relative density of Magnesium-aluminate spinel (MAS), the maximum hardness, and the maximum transmittance are 96.19%, 18.18 GPa, and 36.3%, respectively. Under the optimum conditions, when the mass of the sample is 0.2 g, the relative density and maximum hardness of the Magnesium-aluminate spinel (MAS) sample are 97.28% and 18.18 GPa, respectively. Although the transmittance is not the highest, it is only lower than the transmittance of 0.15 g sample. The optimum sintering additive content and sample thickness jointly promote the densification, hardness, and transmittance of Magnesium-aluminate spinel (MAS). [ABSTRACT FROM AUTHOR]

Cobalt (Co)‐based oxides show promising activity as precious metal‐free catalysts for the oxygen evolution reaction in proton exchange membrane water electrolysis, but the dissolution of Co has limited the durability of Co3O4 at industrially relevant current densities. This work demonstrates that cation in an octahedral coordination environment accounts for the oxygen evolution activity. Using a mixed inverse‐normal phase spinel CoxGa(3‐x)O4 as a proof‐of‐concept example, the designed Co2+‐O‐Co3+ motifs in octahedral sites trigger oxygen evolution through a kinetically favorable radical coupling pathway. Furthermore, lattice oxygen exchange, a leading factor in catalyst structural degradation for normal Co3O4, is suppressed, as evidenced by isotopic labeling experiments and theoretical calculations. With the optimized catalyst, Co1.8Ga1.2O4, an overpotential of 310 mV at 10 mA cm−2 is reported, with stable operation at 200 mA cm−2 for 200 h in a three‐electrode setup, and a proton exchange membrane electrolyzer operating at 200 mA cm−2 for 450 h. [ABSTRACT FROM AUTHOR]

Interest in high‐entropy inorganic compounds originates from their ability to stabilize cations and anions in local environments that rarely occur at standard temperature and pressure. This leads to new crystalline phases in many‐cation formulations with structures and properties that depart from conventional trends. The highest‐entropy homogeneous and random solid solution is a parent structure from which a continuum of lower‐entropy offspring can originate by adopting chemical and/or structural order. This report demonstrates how synthesis conditions, thermal history, and elastic and chemical boundary conditions conspire to regulate this process in Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, during which coherent CuO nanotweeds and spinel nanocuboids evolve. We do so by combining structured synthesis routes, atomic‐resolution microscopy and spectroscopy, density functional theory, and a phase field modeling framework that accurately predicts the emergent structure and local chemistry. This establishes a framework to appreciate, understand, and predict the macrostate spectrum available to a high‐entropy system that is critical to rationalizing property engineering opportunities. [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]

Spinel ferrites demonstrate extensive applications in different areas, like electrodes for electrochemical devices, gas sensors, catalysts, and magnetic adsorbents for environmentally important processes. However, defects in the real spinel structure can change the many physical and chemical properties of spinel ferrites. Although the number of defects in a crystal spinel lattice is small, their influence on the vast majority of physical properties could be really decisive. This review provides an overview of the structural characteristics of spinel compounds (e.g., CoFe2O4, NiFe2O4, ZnFe2O4, Fe3O4, γ–Fe2O3, Co3O4, Mn3O4, NiCo2O4, ZnCo2O4, Co2MnO4, etc.) and examines the influence of defects on their properties. Attention was paid to the classification (0D, 1D, 2D, and 3D defects), nomenclature, and the formation of point and surface defects in ferrites. An in-depth description of the defects responsible for the physicochemical properties and the methodologies employed for their determination are presented. DFT as the most common simulation approach is described in relation to modeling the point defects in spinel compounds. The significant influence of defect distribution on the magnetic interactions between cations, enhancing magnetic properties, is highlighted. The main defect-engineering strategies (direct synthesis and post-treatment) are described. An antistructural notation of active centers in spinel cobalt ferrite is presented. It is shown that the introduction of cations with different charges (e.g., Cu(I), Mn(II), Ce(III), or Ce(IV)) into the cobalt ferrite spinel matrix results in the formation of various point defects. The ability to predict the type of defects and their impact on material properties is the basis of defect engineering, which is currently an extremely promising direction in modern materials science. [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]

Spinel oxides have emerged as highly active catalysts for the oxygen evolution reaction (OER). Owing 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 within 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 also verified by pH‐dependent behavior and in situ Raman analysis. The 18O‐labeled electrochemical mass spectrometry provides direct evidence that the oxygen released during the OER originates from the lattice oxygen of Ce−NiCo2O4. We discover 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] unit site, thereby activating lattice oxygen redox of NiCo2O4 in OER. This work provides a new perspective for designing highly active spinel oxides for OER and offers significant insights into the rare‐earth‐enhanced LOM mechanism. [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]

The electrochemical hydrogen evolution reaction (HER) was considered to be a promising strategy for future clean energy. In this work, a composite electrocatalyst (designated as CGO36@CC) was synthesized through anchoring of nano spinel structure Co2GeO4 onto carbon cloth fibers and exhibited outstanding electrocatalytic performance for HERs in an alkaline medium. The characterization outcome established that, after 36 h of hydrothermal reaction, nano spinel structure Co2GeO4 particles (exposed abundant 111 crystal planes) were stably loaded onto a carbon cloth fiber surface, and this structural configuration facilitated the electrons transferring between each other. In addition, the electrochemical analysis revealed that the incorporation of nano spinel structure Co2GeO4 and carbon cloth significantly augmented the electrochemical activity value of the composite and efficiently enhanced the HER performance. Notably, the overpotential was merely 96 mV at 10 mA·cm−2 current density, and the Tafel slope was only 48.9 mV·dec−1. Moreover, CGO36@CC displayed remarkable catalytic activity and sustained HER catalytic stability. The theoretical catalytic prowess of CGO36@CC stemmed from the collaborative influence of germanium and cobalt atoms within the exposed 111 crystal plane of the Co2GeO4 molecular framework. The amalgamation of Co2GeO4 with carbon cloth fiber conferred upon the composite electrocatalyst both superior theoretical catalytic activity and enhanced electron transfer capability. This work provides a novel strategy for exploring a highly efficient composite electrocatalyst combined transition metal with carbon material to accelerate the HER activity. [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]

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]

MnZn ferrite powders were prepared based on the novel nano in situ composite method and through chemical sol-spray drying–calcination technology. The precursor powders were calcined at 1060 °C at different calcination times (1–9 h) to research the influences of the calcination time on MnZn ferrite powders. The research results revealed that all samples had similar morphologies composed of fine particles. The pure MnZn ferrite spinel phase can only be obtained when the calcination time does not exceed 3 h. Otherwise, some α-Fe2O3 or γ-Fe2O3 impurities will appear. The particle size descended with an increasing calcination time and then ascended. After 3 h of preservation, the smallest particle size was obtained, and it exhibited a unimodal distribution. The saturation magnetization (Ms) increased at first and decreased later with an increasing calcination time, and the optimal value (53.4 emu/g) was reached after holding for 3 h. In view of this work, the optimal calcination time is 3 h. [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 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]