Synergistic design of a semi-hollow core-shell structure and a metal-organic framework-derived Co/Zn selenide coated with MXene for high-performance lithium-sulfur batteries.

Lithium-sulfur batteries have garnered significant interest as potential energy storage systems for the future, owing to their remarkable theoretical specific capacity (1675 mA h g-1) and energy density (2600 W h kg-1). However, their development has been severely impeded by several challenges, including the low intrinsic conductivity of sulfur, volume expansion issues, and the polysulfide shuttle effect. To address these issues, polar metal compounds with nanostructures featuring hollow shells and catalytic functions have emerged as promising materials for designing advanced lithium-sulfur batteries. In this study, bimetallic selenides with varying degrees of hollowness are synthesized using a tannic acid etching and selenization strategy. By comparing the electrochemical characteristics of composite electrodes with different degrees of hollowness, an optimal semi-hollow core-shell structure is identified, implying that reasonable structural designing of metal compounds carries immense importance in improving electrochemical reactions. Moreover, the appropriate degree of hollowness effectively mitigates volume expansion issues associated with the sulfur cathode. Consequently, bimetallic selenides with a hollow core-shell structure coated with conductive MXene material exhibit superior electrochemical performance. The synergistic effect achieved through the judicious design of the hollow core-shell structure and the utilization of polar metal compounds has proved instrumental in enhancing the redox kinetics of lithium-sulfur batteries. As such, this research presents a novel avenue for the development of high-performance lithium-sulfur batteries.

Contribution of boundary non-stoichiometry to the lower-temperature plasticity in high-pressure sintered boron carbide.

The improvement of non-oxide ceramic plasticity while maintaining the high-temperature strength is a great challenge through the classical strategy, which generally includes decreasing grain size to several nanometers or adding ductile binder phase. Here, we report that the plasticity of fully dense boron carbide (B4C) is greatly enhanced due to the boundary non-stoichiometry induced by high-pressure sintering technology. The effect decreases the plastic deformation temperature of B4C by 200 °C compared to that of conventionally-sintered specimens. Promoted grain boundary diffusion is found to enhance grain boundary sliding, which dominate the lower-temperature plasticity. In addition, the as-produced specimen maintains extraordinary strength before the occurrence of plasticity. The study provides an efficient strategy by boundary chemical change to facilitate the plasticity of ceramic materials.

Crystal Structure and Bond-Valence Investigation of Nitrogen-Stabilized LiAl5O8 Spinels.

An in-depth insight into the effect of nitrogen substitution on structural stabilization is important for the design of new spinel-type oxynitride materials with tailored properties. In this work, the crystal structures of ordered and disordered LiAl5O8 obtained by slow cooling and rapid quenching, respectively, were analyzed by a X-ray diffraction (XRD) Rietveld refinement and OccQP program. The variation in the bonding state of atoms in the two compounds was explored by the bond valence model, which revealed that the instability of spinel-type LiAl5O8 crystal structure at room temperature is mainly due to the severe under-bonding of the tetrahedrally coordinated Al cations. With the partial substitution of oxygen with nitrogen in LiAl5O8, a series of the nitrogen-stabilized spinel LiyAl(16+x-y)/3O8-xNx (0 < x < 0.5, 0 < y < 1) was successfully prepared. The crystal structures were systematically investigated by the powder XRD structural refinement combined with 7Li and 27Al magic-angle spinning nuclear magnetic resonance. All the Li+ ions entered the octahedra, while the Al resonances may be composed of multiple non-equivalent Al sites. The structural stability of spinel LiyAl(16+x-y)/3O8-xNx at ambient temperature was attributed to the cationic vacancies and high valence generated by the N ions, which alleviated the under-bonding state of the tetrahedral Al-O bond. This work provides a new perspective for understanding the composition-structure relationship in spinel compounds with multiple disorders.

Elasticity of Nonstoichiometric Alumina-Rich Spinel Determined by Bond Valence Theory and Brillouin Scattering.

An accurate knowledge of the elastic properties of materials is essential for material science and engineering applications. Four single crystals of nonstoichiometric alumina-rich spinel [Mg1-xAl2(1+x/3)O4] were obtained from sintered transparent ceramics for the investigation of its elastic properties. The disordered crystal structures were fully resolved by combining single-crystal structure refinement and a quadratic programming approach for the first time. The bond valence model and Brillouin scattering experiments were used to evaluate the bulk modulus (K), shear modulus (G), Young's modulus (E), and Poisson's ratio. The discrepancy between the theoretical and experimental results is <2.6%. The independent elastic constants (C11, C12, and C44) were determined from Brillouin scattering experiments. A negative Poisson's ratio, υ(110, 11̅0), was found to exist in all alumina-rich spinels, which means it is a partially auxetic material. Blackman diagram analysis was introduced to identify the interrelationships and trends in mechanical and bonding properties in alumina-rich spinels. The bond valence model was suggested to be an effective and accurate approach for predicting the elastic modulus of spinels, which provides a useful tool for the study of the composition-structure-property relationship of materials.

Structural Study of MgyAl(8+x-2y)/3O4-xNx (0 < x < 0.5, 0 < y < 1) Spinel Probed by X-ray Diffraction, 27Al MAS NMR, and First-Principles Calculations.

The deep understanding of the crystal structure and composition-structure relationship is important for modifying and designing solids to obtain functional materials with customized properties. However, because of multiple compositions and complex structures in some spinel solid solutions, the composition-structure relationship is unknown, or becomes very complicated and difficult to be controlled. In this work, the solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) technique and powder X-ray diffraction (XRD) Rietveld refinement were combined to characterize the crystal structure of quaternary disordered MgyAl(8+x-2y)/3O4-xNx solid solutions in detail, which was supported by the first-principles density functional theory calculations. Diffraction data indicate that Mg ions preferentially enter the tetrahedron structure in MgyAl(8+x-2y)/3O4-xNx solid solutions because the sum of the bond valence in tetrahedron is closer to the atomic valence of Mg. With the compositional change, the coordination polyhedra in the crystal structure will also adjust the volume according to the changes in lattice parameter, anion parameter, and inversion parameter. In addition, the populations, chemical shifts, and quadrupole coupling constants of Al located in different coordinated environments of the solid solutions were detected through the simulation and integration of 27Al MAS NMR spectra, which were related to the structural parameters by the bond valence method. It turns out that 27Al MAS NMR parameters are highly sensitive to the subtle changes in the local environment of Al caused by the preferential occupation of Mg in the tetrahedron. These results provide deep insights into the crystal structural details of novel spinel materials with multiple disorders.

Uranyl Organic Framework as a Highly Selective and Sensitive Turn-on and Turn-off Luminescent Sensor for Dual Functional Detection Arginine and MnO4.

Five new uranyl coordination polymers were prepared by the hydrothermal method based on 5-nitroisophthalic acid (H2nip) as (UO2)(nip)(2,2'-bpy) (1), (H24,4'-bpy)·[(UO2)3(nip)4]·(4,4'-bpy) (2), (H2bpe)·[(UO2)0.5(nip)] (3), (H2 bpp)·[(UO2)2-(nip)3]·H2O (4), and (H2tmp)·[(UO2)(nip)2](5) [2,2'-bpy = 2,2'-bipyridine, 4,4'-bpy = 4,4'-bipyridine, bpe = 4,4'-vinylenedipyridine, bpp = 4,4' -trimethylenedipyridine, tmp = tetramethylpyrazine]. All of these synthesized complexes have been characterized by single crystal and powder X-ray diffraction, IR spectra, thermogravimetric analysis, elemental analysis, and luminescent properties. In particular, it is found that compounds 1 and 4 can be used as a luminescent sensor to efficiently detect arginine in aqueous solution by means of "turn-on"; the detection limits were 1.06 × 10-6 and 6.42 × 10-6 mol/L, respectively. Moreover, 4 can also be used as a bifunctional sensor for selective sensing of MnO4- anion by "turn-off". The detection limit of MnO4- in water was 1.79 × 10-6 mol/L; the Ksv was 1.88 × 104. The sensing effect of arginine in simulated grape juice samples and MnO4- in simulated river water samples was also investigated by this sensing system with high recovery. In addition, the possible mechanism of sensing arginine and MnO4- in the aqueous solution was discussed.

Magic Angle Spinning NMR Study on Inversion Behavior and Vacancy Disorder in Alumina-Rich Spinel.

Solid state magic angle spinning nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) were used to investigate the inverse behavior and vacancy disorder in alumina-rich spinel, Mg1- xAl2(1+ x/3)O4 (0 ≤ x ≤ 0.86). Simulation and integration of NMR spectra have been developed for probing the population of Al located in different coordinated environments. Rietveld profile refinements were performed for powder XRD spectra by combining with NMR analysis. With changes in the composition, inversion disorder and cationic vacancies coexisting in tetrahedral and octahedral coordinations fluctuate in amount in the crystal lattice. The coordination polyhedra in the crystal structure can adjust the volume to variations of composition, anion parameter, and inverse parameter. This opens a window to the design and functionalization of spinel materials.

Variation of Structure and Photoluminescence Properties of Ce3+ Doped MgAlON Transparent Ceramics with Different Doping Content.

Transparent MgAlON:Ce fluorescent ceramics with doping content of 0.005, 0.01, and 0.02 at % were fabricated by pressureless sintering. All the samples were dense and large in grain size. Under the excitation of 320 nm UV, the samples emitted blue lights centered around 410 nm. The 0.005 and 0.01 at % Ce3+ doped samples were single phase by XRD detection, and possessed good optical and mechanical properties, and luminous thermal stability. The fluorescence lifetime, the CL and PL spectra analysis, indicated that most of the luminous centers were segregated in GB, and there was still a small part of second phase existing in 0.01 at % Ce3+ doped sample, which revealed that spectroscopy methods possessed better sensitivity in smaller scale and lower concentration detection than XRD. As the doping content increasing to 0.02 at %, a mass of second phase arose, which resulted in the optical transparency, mechanical property, luminous thermal stability decline, and the PL spectra red shift by the formation of second phase. It revealed that the performances were fatally deteriorated by excess doping of Ce3+ ions.

Combining 27Al Solid-State NMR and First-Principles Simulations To Explore Crystal Structure in Disordered Aluminum Oxynitride.

The nuclear magnetic resonance (NMR) technique gives insight into the local information in a crystal structure, while Rietveld refinement of powder X-ray diffraction (PXRD) sketches out the framework of a crystal lattice. In this work, first-principles calculations were combined with the solid-state NMR technique and Rietveld refinement to explore the crystal structure of a disordered aluminum oxynitride (γ-alon). The theoretical NMR parameters (chemical shift, δiso, quadrupolar coupling constants, CQ, and asymmetry parameter, η) of Al22.5O28.5N3.5, predicted by the gauge-including projector augmented wave (GIPAW) algorithm, were used to facilitate the analytical investigation of the 27Al magic-angle spinning (MAS) NMR spectra of the as-prepared sample, whose formula was confirmed to be Al2.811O3.565N0.435 by quantitative analysis. The experimental δiso, CQ, and η of 27Al showed a small discrepancy compared with theoretical models. The ratio of aluminum located at the 8a to 16d sites was calculated to be 0.531 from the relative integration of peaks in the 27Al NMR spectra. The occupancies of aluminum at the 8a and 16d positions were determined through NMR investigations to be 0.9755 and 0.9178, respectively, and were used in the Rietveld refinement to obtain the lattice parameter and anion parameter of Al2.811O3.565N0.435. The results from 27Al NMR investigations and PXRD structural refinement complemented each other. This work provides a powerful and accessible strategy to precisely understand the crystal structure of novel oxynitride materials with multiple disorder.

Chemical composition, crystal structure, and their relationships with the intrinsic properties of spinel-type crystals based on bond valences.

Spinel-type crystals may possess complex and versatile chemical composition and crystal structure, which leads to difficulty in constructing relationships among the chemical composition, crystal structure, and intrinsic properties. In this work, we develop new empirical methods based on bond valences to estimate the intrinsic properties, namely, compressibility and thermal expansion of complex spinel-type crystals. The composition-weighted average of bond force constants in tetrahedral and octahedral coordination polyhedra is derived as a function of the composition-weighted average of bond valences, which can be calculated according to the experimental chemical composition and crystal structural parameters. We discuss the coupled effects of tetrahedral and octahedral frameworks on the aforementioned intrinsic properties. The bulk modulus could be quantitatively calculated from the composition-weighted average of bond force constants in tetrahedral and octahedral coordination polyhedra. In contrast, a quantitative estimation of the thermal expansion coefficient could be obtained from the composition-weighted average of bond force constants in octahedral coordination polyhedra. These empirical methods have been validated by the results obtained for a new complex quaternary spinel-type oxynitride Mg0.268Al2.577O3.733N0.267 as well as MgAl2O4 and Al2.85O3.45N0.55 from the literature. Further, these empirical methods have the potential to be extensively applied in other types of complex crystals.

Bis(1,10-phenanthroline-κN,N')(phenyl-acetato-κO)copper(II) phenyl-acetate hexa-hydrate.

In the title compound, [Cu(C(8)H(7)O(2))(C(12)H(8)N(2))(2)](C(8)H(7)O(2))·6H(2)O, the Cu atom is in a distorted square-pyramidal coordination environment. The six crystallographically independent uncoordinated water mol-ecules are inter-connected by hydrogen bonds, completing dodeca-water (H(2)O)(12) clusters which are hydrogen bonded to the carboxyl-ate groups of phenyl-acetate anions, building up one-dimensional anionic chains propagating along [100]. Between the cationic and anionic chains are hydrogen bonds from water mol-ecules to the carboxyl-ate O atoms belonging to the phenyl-acetato ligands.