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The detailed chemical bond parameters of Ln[Al.sub.3](B[O.sub.3]).sub.4] crystals were calculated using the chemical bond theory of complex crystals. Results indicated that Ln-O bonds are ionic and B-O bonds possess higher covalency. The environment factor defined by electron polarizabilities and covalency was employed to predict Racah parameters. The hardness of Y[Al.sub.3](B[O.sub.3]).sub.4] was predicted using Gao's model, which is also in agreement with the experimental value. Key words: dielectric properties, hardness. Resume : On a calcule les parametres detailles des liaisons chimiques dans les cristaux de LnAl3(B03)4 en faisant appel a la theorie de la liaison chimique dans les cristaux. Les resultats indiquent que les liaisons Ln-O sont ioniques alors que les liaisons B-O possedent un degre important de covalence. On a fait appel au facteur d'environnement defini par les polarisabilites et la covalence pour predire les parametres de Racah. La valeur de la durete du Y[Al.sub.3](B[O.sub.3]).sub.4] qui a ete predite sur la base du modele de Gao est aussi en accord avec la valeur experimentale. Mots-cles : proprietes dielectriques, durete. [Traduit par la Redaction], Introduction The huntite-type borate Ln[Al.sub.3](B[O.sub.3]).sub.4] was synthesizd by Ballman in 1962 and the structures of Y[Al.sub.3](B[O.sub.3]).sub.4], Nd[Al.sub.3] (B[O.sub.3]).sub.4], and Gd[Al.sub.3](B[O.sub.3]).sub.4] were reported. (1) Y[Al.sub.3](B[O.sub.3]).sub.4] was found to have excellent nonlinear [...]

Using the chemical bond theory of dielectric description, the chemical bond parameters of the M-, W-type hexagonal barium ferrites were calculated. The hardness of Ba[Fe.sub.12][O.sub.19] and BaFe18O27 were calculated. The calculated hardness of Ba[Fe.sub.12][O.sub.19] is 5.9 GPa, which is in agreement with the experimental values. The calculated hardness of planes parallel to the c axis of Ba[Fe.dub.18][O.sub.27] is 5.5 GPa, which is smaller than that of Ba[Fe.sub.12][O.sub.19]. PACS Nos: 62.20.Qp, 71.10.2w Key words: bonding, hardness, ferrites. Faisant appel a la theorie de la liaison chimique de la description dielectrique, on a calcule les parametres de la liaison chimique des ferrites de baryum de type-M et W. On a calcule la durete du Ba[Fe.sub.12][O.sub.19] et du Ba[Fe.dub.18][O.sub.27]. La durete calculee du Ba[Fe.sub.12][O.sub.19] est de 5,9 GPa, qui est en accord avec les valeurs experimentales. La durete des plans paralleles a l'axe c du Ba[Fe.dub.18][O.sub.27] est de 5,5 GPa qui est inferieure a celle du Ba[Fe.sub.12][O.sub.19]. Mots-cles : liaison, durete, ferrites. [Traduit par la Redaction], Introduction Ferrite materials are particularly excellent in wear resistance and chemical stability. Therefore, the protective layer on the surface of medium is dispensable, leading to a great advantage for high-density [...]

Boron carbonitride (BCN) nanotubes have been successfully prepared using N[H.sub.4]Cl, KB[H.sub.4], and Zn[Br.sub.2] as the reactants at 480 °C for 12 h by a new benzene-thermal approach in a [N.sub.2] atmosphere. As its by-product, a new form of carbon regular hexagonal nanocages are observed. The samples are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), transmission electron diffraction (TED), electron energy loss spectroscopy (EELS), and high-resolution transmission electron microscopy (HRTEM). The prepared nanotubes have uniform outer diameters in the range of 150 to 500 nm and a length of up to several micrometerss. The novel carbon hexagonal nanocages have a typical size ranging from 100 nm to 1.5 µm, which could be the giant fullerene cages of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (N = 17 ~ 148). So, high fullerenes are observed for the first time. The influences of reaction temperature and Zn[Br.sub.2] on products and the formation mechanism of BCN nanotubes are discussed. Key words: boron carbonitride (BCN) nanotube, benzene thermal, giant fullerene. On a prepare; avec succes des nanotubes BCN par reaction de N[H.sub.4]Cl, de KB[H.sub.4] et de Zn[Br.sub.2], a 480 °C pendant 12 h, en faisant appel a une nouvelle approche de benzene-thermal dans une atmosphere d'azote. On a aussi observe: la formation comme sous-produit d'une nouvelle forme de nanocages hexagonales regulieres a base de carbone. Les echantillons ont ete caracterises par diffraction des rayons-X (DRX), par spectroscopie infrarouge a transformation de Fourier (IRTF), par microscopie electronique de transmission (MET), par diffraction electronique de transmission (DET), par spectroscopie de la perte d'energie electronique (SPEE) et par microscopie electronique de transmission a haute resolution (METHR). Les nanotubes prepares posseedent des diameetres exterieurs uniformes allant de 150 a 500 nm et des longueurs allant jusqu'a plusieurs microns. La tailles typiques des nouvelles nanocages hexagonales a base de carbone vont de 100 nm a 1.5 µm qui s'apparentent aux cages de fullerenes geeants de [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (N = 17 ~ 148). On a donc observe des fullerenes geants pour la premiere fois. On discute aussi de l'influence de la temperature reeactionnelle et du Zn[Br.sub.2] sur les produits et sur le mecanisme de formation des nanotubes BCN. Mots-cles: nanotube BCN, benzene-thermal, fullerene geant. [Traduit par la Redaction], Introduction It is well-known that the boron carbonitride (BCN) compounds are promising superhard materials. (1,2) Theoretical calculations have revealed that the ternary BCN compounds, depending on the structure and composition, [...]

In recent years, 2D intercalated pseudocapacitance MoO3 and Nb2O5 have been widely investigated, while 3D Mo-Nb–O materials have rarely been discussed. Here, we synthesized Mo3Nb2O14-B by a simple ball-milling method and further prepared Mo3Nb2O14-L with advanced energy storage properties by a solvothermal method, where the abundant nanopore channels and in situ carbon encapsulation led to fast Li-ion diffusion and excellent structural stability. It performs well in half-cell performance tests, including high reversible capacity (461 mAh g−1 at 0.1C), initial coulomb efficiency of 88.4%, excellent cycling performance (4.4% capacity loss in 600 cycles at 10 C), and significant intercalation mimetic capacitive contribution (89.2% at 1.0 mV s). All these advantages indicate that Mo3Nb2O14-L has great potential for use as anode material for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) play a crucial role in lithium-ion batteries (LIBs) due to their high theoretical capacity, natural abundance, and benign environmental impact, but they suffer from limitations such as cyclability and high-rate discharge ability. One leading cause is the lithiation-induced volume expansion (LIVE) for "conversion"-type TMOs, which can result in high stress, fracture and pulverization. Using carbon layers is an effective strategy to provide effective volumetric accommodation for lithium-ion (Li+) insertion; however, the detailed mechanism is unknown. In order to clarify the working mechanism of nanoscale LIBs, herein, the discharge reactions in a nanoscale LIB were investigated through in situ environmental transmission electron microscopy (ETEM). Visualization of the Li+ insertion process of MnO@C nanorods (NRs) with core/shell structure (CSS) and internal void space (IVS) was achieved. The LIVE occurred in a consecutive two-step mode, i.e., a LIVE of the carbon layer followed by a co-LIVE of the carbon layer and MnO. No volume contraction of the IVS was observed. The IVS acted as a buffer relieving the stress of the carbon layer. The carbon layer with IVS simultaneously improved the cyclability and the high-rate discharge ability of the electrode, pointing to a promising route for building better TMO electrode materials. [ABSTRACT FROM AUTHOR]

Silicon‐based lithium‐ion battery anodes, in recent years, have caught widespread interest seeing their great theoretical capacity, low charge‐discharge potentials, and ample natural storage. However, poor electrochemical performance is typically observed, attributed mainly to significant volume expansion, unstable solid‐electrolyte interphase, and low intrinsic electronic/ionic conductivity. Numerous attempts have been reported to revamp its electrochemical performance, including the capacity cycle stability and cycle life. Herein, we reported the synthesis of three‐dimensional (3D) Si@TiO2@C nanohybrids adopting a facile three‐step synthesis strategy. Compared with Si@C and C (derived from polyaniline) electrodes, the well‐designed Si@TiO2@C electrode delivered a momentous enhancement in the electrochemical performance thanks to the presence of robust TiO2 shell and polyaniline‐derived porous carbon skeleton to cope with volume changes of silicon during lithiation and promote the electric conductivity of the overall electrode. The Si@TiO2@C hybrid electrode delivered a high initial discharge capacity of 1748.6 mA h g−1 at 100 mA g−1 and a stable reversible capacity of 1112.5 mA h g−1 at 100 mA g−1 after 500 cycles, with the coulomb efficiency of 98.8 %. Moreover, the electrode showed a high reversible capacity of 508.9 mA h g−1 even at 500 mA g−1 at the 500th cycle with the coulomb efficiency of 99.1 %. This work showed the paramount role of TiO2 shell and 3D porous carbon skeleton, being a promising future for designing the next generation of high capacity, long cycle stable anode materials for lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

An electrochemical catalyst with efficient, stable, inexpensive energy storage for oxygen evolution and hydrogen evolution has raised global concerns on energy, calling for high-performance materials for effective treatments. In this paper, novel amorphous polymetallic doped CeO2 particles were prepared for an electrochemical catalyst via homogeneous phase precipitation at room temperature. Metal ions can be easily embedded into the oxygen vacancies formed by CeO2, and the the electron transport capacity of the CeO2/NiFeCo electrocatalyst is improved owing to the increase in active sites. In addition, the amorphous CeO2/NiFeCo composite material is in a metastable state and will transform into different active states in a reducing or oxidizing environment. Furthermore, the amorphous material drives oxygen evolution reaction (OER) through the lattice oxygen oxidation mechanism (LOM), while LOM can effectively bypass the adsorption of strongly related intermediates in the adsorbate release mechanism, thus promoting OER procedure in a timely manner. As a result, CeO2/NiFeCo exhibits a lower oxygen evolution overpotential of 260 mV at 10 mA cm−2 current density, which shows a predatorily competitive advantage compared with commercially available RuO2 and the reported catalysts. [ABSTRACT FROM AUTHOR]

Fe2O3@OMC (ordered mesoporous carbon) is synthesized using Fe-MOFs (metal-organic frameworks). The Fe2O3@OMC pore size is mostly concentrated at approximately 2–4 nm. Compared to traditional OMC or carbonized Fe-MOFs, Fe2O3@OMC demonstrates a higher capacity (the capacity remains at 1176.6 mAh g−1 after 500 cycles under a current density of 0.1 A g−1) and a longer cycle life. The first cycle capacity of Fe2O3@OMC is ultrahigh at 2448.6 mAh g−1, and the reversible capacity is 1294.1 mAh g−1. Fe2O3@OMC maintains a good performance under current densities of 0.1 A g−1, 0.2 A g−1, 0.5 A g−1, 1 A g−1, 2 A g−1, and 5 A g−1, with electric capacities of 1100.8 mAh g−1, 1017.6 mAh g−1, 849.3 mAh g−1, 690.7 mAh g−1, 506.7 mAh g−1, and 272.1 mAh g−1, respectively. Thus, the material has good rate performance. Combining iron oxide and MOFs is helpful to improve the capacity performance. [ABSTRACT FROM AUTHOR]