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The paper describes a heterobimetallic mixed-ligand hexanuclear precursor [NaMn[sub.2](thd)[sub.4](OAc)][sub.2] (1) (thd = 2,2,6,6-tetramethyl-3,5-heptadionate; OAc = acetate) that was designed based on its lithium homoleptic analogue, [LiMn[sub.2](thd)[sub.5]], by replacing one of the thd ligands with an acetate group in order to accommodate 5-coordinated sodium instead of tetrahedral lithium ion. The complex, which is highly volatile and soluble in a variety of common solvents, has been synthesized by both the solid-state and solution methods. The unique “dimer-of-trimers” heterometallic structure consists of two trinuclear [NaMn[sup.II] [sub.2](thd)[sub.4]][sup.+] units firmly bridged by two acetate ligands. X-ray diffraction techniques, DART mass spectrometry, ICP-OES analysis, and IR spectroscopy have been employed to confirm the structure and composition of the hexanuclear complex. Similar to the Li counterpart forming LiMn[sub.2]O[sub.4] spinel material upon thermal decomposition, the title Na:Mn = 1:2 compound was utilized as the first single-source precursor for the low-temperature preparation of Na[sub.4]Mn[sub.9]O[sub.18] tunnel oxide. Importantly, four Mn sites in the hexanuclear molecule can be potentially partially substituted by other transition metals, leading to heterotri- and tetrametallic precursors for the advanced quaternary and quinary Na-ion oxide cathode materials.

Spinels are important materials for an application in bioimaging. The key advantage with spinel-type hosts is the presence of antisite defects, which act as charge reservoirs for trapping electrons and holes at complementary defect sites. This makes them a host system similar to a molecular system. Herein, we present a systematic approach to modulating the band gap of an inverse Zn[sub.2]TiO[sub.4] spinel. With a change in ZnO concentration, the absorption band at 375 nm diminishes and disappears at a ZnO:TiO[sub.2] concentration of 1.40:1.00. The band gap of the material is modified from 3.30 to 4.40 eV. The crystal structure of the sample does not change drastically as determined using X-ray diffraction and Rietveld refinement. The Zn[sub.2]TiO[sub.4] emits in the UV-A region with a lifetime in the time domain of ‘ns’. The sample also shows persistent luminescence of at least 15 min upon excitation with 254 nm with prominent emission in the UV-A region (300–390 nm). The present results open a new avenue for the synthesis of spinel hosts where the band gap can be modified with ease. The UV emission thus observed is expected to find usage in interesting applications like photocatalysis, anti-counterfeiting, water disinfecting, etc.

Cuprate delafossite phases such as CuMnO[sub.2] (crednerite) and CuFeO[sub.2], as well as iron- and manganese-doped mcconnellite composites, were investigated as candidates for producing intense black ceramic pigments via conventional solid-state synthesis. Both electric kiln and fast dielectric (microwave) firing methods were employed, with mcconnellite (CuCrO[sub.2]) used as a reference pigment. Microwave firing led to a marked improvement in sample blackness compared to conventional electric firing. Among the delafossite phases, only mcconnellite subjected to microwave-assisted firing (R[sub.Vis] = 1.40%, corresponding to 98.60% visible light absorption) emerges, pending further optimization, as a promising candidate for an ultra-black ceramic pigment (R[sub.Vis] < 1%) under optimized glaze conditions (ZnO-free) and a firing temperature of 1000 °C. Considering the pigments in powder form, microwave-fired crednerite (R[sub.Vis] = 4.85%, 95.15% absorption) and iron- and iron–manganese-doped mcconnellite composites (R[sub.Vis] = 3.27% and 3.23%, respectively) appear as potential candidates for deep-black pigments (R[sub.Vis] < 3%), benefiting from the composite effect between the delafossite phase and the associated chromium spinel. Moreover, microwave-fired crednerite also demonstrates noteworthy potential for deep-black coloration in glazed samples (R[sub.Vis] = 4.27%, 95.73% absorption).

The catalytic performance of spinel oxide NiCo.sub.2O.sub.4 for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was investigated. It shows that NiCo.sub.2O.sub.4 synthesized via hydrothermal treatment at 90 â followed by calcination at 350 â exhibits excellent catalytic activity. Furthermore, Fe-doped MnO.sub.2 (marked as Fe-M) was introduced as a modifier to further improve the performance of NiCo.sub.2O.sub.4. As expected, the 20% Fe-M hybrid catalyst (NiCo.sub.2O.sub.4 modified with 20 wt% Fe-M) displays the best ORR and OER catalytic activity. This is evidenced by its high OER current density of 265 mA cm.sup.-2, high ORR current density of 220 mA cm.sup.-2, low OER Tafel slope of 119 mV dec.sup.-1, low ORR Tafel slope of 167 mV dec.sup.-1. These exceptional results can be attributed to the synergistic effect between NiCo.sub.2O.sub.4 and Fe-M.

This research deals with the synthesis of undoped and Sm.sup.3+-doped ZnAl.sub.2O.sub.4 using the citrate sol-gel method. Various complementary techniques have extensively studied the consequences of samarium ion (Sm.sup.3+) doping on the crystallinity and emission mechanism. XRD analysis endorses the formation of Sm.sup.3+-doped ZnAl.sub.2O.sub.4 spinel powder within the size range of 14-26 nm. The granular surface morphology of the prepared samples and their particle size distribution were examined by SEM and TEM, respectively. The direct bandgap of the doped samples was calculated (2.77-3.65 eV) using the Kubelka-Munk function on the diffuse reflectance data. At high concentrations of Sm.sup.3+, photoluminescence (PL) results demonstrate orange-red emission at 597 nm after providing energy corresponding to direct excitation (396 nm) of Sm.sup.3+ ion. The blue-green emission is obtained first time in Sm.sup.3+-doped ZnAl.sub.2O.sub.4 at [lambda].sub.ex = 320 nm excitation wavelength. The CIE chromaticity coordinates indicated that the prepared samples could be applied as an efficient phosphor in the visible range.

The influence of Mg doping in α-Al[sub.2]O[sub.3] crystals is investigated in this article by first-principles calculations and formation energies, density of states, and computed absorption spectra. Three models related to Mg[sup.2+] substituting for Al[sup.3+] doping structures were constructed, as well as spinel structure models with varying aluminum-magnesium ratios. The formation energy calculations confirmed the rationality of the Mg[sub.Al]V[sub.O] model, which means that Mg substitutional doping incorporating oxygen vacancies is most likely to form in crystals. The combined action of magnesium and oxygen vacancies introduced new defect energy levels in the bandgap. The calculated absorption spectra of the Mg[sub.Al]V[sub.O] and Mg-rich spinel structures exhibited various color centers. The experimental absorption spectra and thermoluminescence characteristics of α-Al[sub.2]O[sub.3]:Mg and alumina-magnesium (Al-Mg) spinel crystal samples were tested. The thermoluminescence peak of the Al-Mg spinel was significantly stronger than that of the α-Al[sub.2]O[sub.3]:Mg crystal. The consistency between the model-calculated absorption spectra and the experimental results confirmed the theoretical predictions. Based on the experimental and computational results, the influence of Mg[sup.2+] substitutional doping in α-Al[sub.2]O[sub.3] and the impact of the locally Mg-rich spinel on the optical and radiation performance of α-Al[sub.2]O[sub.3]:Mg crystals are elucidated.

Nonradical Fenton-like catalysis offers opportunities to overcome the low efficiency and secondary pollution limitations of existing advanced oxidation decontamination technologies, but realizing this on transition metal spinel oxide catalysts remains challenging due to insufficient understanding of their catalytic mechanisms. Here, we explore the origins of catalytic selectivity of Fe–Mn spinel oxide and identify electron delocalization of the surface metal active site as the key driver of its nonradical catalysis. Through fine-tuning the crystal geometry to trigger Fe–Mn superexchange interaction at the spinel octahedra, ZnFeMnO₄ with high-degree electron delocalization of the Mn–O unit was created to enable near 100% nonradical activation of peroxymonosulfate (PMS) at unprecedented utilization efficiency. The resulting surface-bound PMS* complex can efficiently oxidize electron-rich pollutants with extraordinary degradation activity, selectivity, and good environmental robustness to favor water decontamination applications. Our work provides a molecule-level understanding of the catalytic selectivity and bimetallic interactions of Fe–Mn spinel oxides, which may guide the design of low-cost spinel oxides for more selective and efficient decontamination applications.

As high-capacity anode materials, spinel NiFe[sub.2]O[sub.4] aroused extensive attention due to its natural abundance and safe working voltage. For widespread commercialization, some drawbacks, such as rapid capacity fading and poor reversibility due to large volume variation and inferior conductivity, urgently require amelioration. In this work, NiFe[sub.2]O[sub.4]/NiO composites with a dual-network structure were fabricated by a simple dealloying method. Benefiting from the dual-network structure and composed of nanosheet networks and ligament-pore networks, this material provides sufficient space for volume expansion and is able to boost the rapid transfer of electrons and Li ions. As a result, the material exhibits excellent electrochemical performance, retaining 756.9 mAh g[sup.−1] at 200 mA g[sup.−1] after cycling for 100 cycles and retaining 641.1 mAh g[sup.−1] after 1000 cycles at 500 mA g[sup.−1]. This work provides a facile way to prepare a novel dual-network structured spinel oxide material, which can promote the development of oxide anodes and also dealloying techniques in broad fields.

Developing stable and efficient electrocatalysts is vital for boosting oxygen evolution reaction (OER) rates in sustainable hydrogen production. High-entropy oxides (HEOs) consist of five or more metal cations, providing opportunities to tune their catalytic properties toward high OER efficiency. This work combines theoretical and experimental studies to scrutinize the OER activity and stability for spinel-type HEOs. Density functional theory confirms that randomly mixed metal sites show thermodynamic stability, with intermediate adsorption energies displaying wider distributions due to mixing-induced equatorial strain in active metal-oxygen bonds. The rapid sol-flame method is employed to synthesize HEO, comprising five 3d-transition metal cations, which exhibits superior OER activity and durability under alkaline conditions, outperforming lower-entropy oxides, even with partial surface oxidations. The study highlights that the enhanced activity of HEO is primarily attributed to the mixing of multiple elements, leading to strain effects near the active site, as well as surface composition and coverage. Efficient and durable electrocatalysts are essential for boosting oxygen evolution reaction toward hydrogen production. Here, the authors report a combined theoretical and experimental study on high-entropy spinel oxide with element mixing and strains providing superior activity and stability.

Enhancing the mechanical strength of transparent glass-ceramics (TGCs) without compromising their optical performance remains a key challenge for advanced optical and photonic materials. Among aluminosilicate systems, ZnO–MgO–Al[sub.2]O[sub.3]–SiO[sub.2] (ZMAS) glasses are particularly attractive due to their ability to form ZnAl[sub.2]O[sub.4]-based nanostructures; however, their ion-exchange (IE) strengthening has not been systematically explored due to the absence of single-charged cations in their composition. In this study, a sodium-modified ZMAS glass was developed to enable efficient chemical strengthening while preserving glass-forming ability and optical clarity. Controlled two-stage heat treatment produced TGCs containing 5 mol% Na[sub.2]O, composed solely of ZnAl[sub.2]O[sub.4] (gahnite) nanocrystals with an average size of 4–5 nm. The obtained TGCs showed a Vickers hardness of ~8.5 GPa, increasing to ~10–10.5 GPa after ion exchange in molten KNO[sub.3] at 450 °C, without changes in phase composition or optical transmittance. Compared with literature data on alkali-containing TGCs, the developed material demonstrates a higher hardness level while maintaining full transparency. The results reveal a practical route toward chemically strengthened ZnAl[sub.2]O[sub.4]-based glass-ceramics combining optical clarity, high hardness, and damage tolerance for optical, photonic, and protective applications.