This work reports on hybrid hexamethylenediaminium lead halide perovskites. The materials were prepared using wet synthesis and the subsequent precipitation from aqueous solution. Structural and morphological charactarization studies show their high degree of crystallinity and phase purity. The determined perovskites' structural parameters agree well with the literature reports. The recorded XPS and DRS data allowed for the first schematic representation of the perovskite band structures. The latter match well the results of DFT modeling. It is shown for the first time that the increase in the perovskite bandgaps is solely due to the increase in the anion electronegativity. Namely, as the anion electronegativity increases, the corresponding valence band energy decreases. In contrast, the electronegativity of the anions has no effect on the perovskite conduction band energies. The presented study deepens our understanding of the relationship between the crystal and electronic structures of low-dimensional hybrid halide perovskites.

Among high-capacity materials for the negative electrode of a lithium-ion battery, Sn stands out due to a high theoretical specific capacity of 994 mA h/g and the presence of a low-potential discharge plateau. However, a significant increase in volume during the intercalation of lithium into tin leads to degradation and a serious decrease in capacity. An efficient method to overcome this drawback is to create composites with nickel or carbon to prevent the occurrence of microstresses. Powders of Sn–Ni samples were produced by the reduction of metals in the liquid phase and analyzed by X-ray powder diffraction analysis. A Sn/carbon nanotubes powder was obtained by heat treatment in a vacuum and studied by scanning electron microscopy. The electrochemical properties of the material were investigated by chronopotentiometry in a three-electrode electrochemical cell. The Sn/carbon nanotube composite material has a much higher capacity than tin nanopowders when cycling at a current density of ~0.1 A/g. It follows from this that the former has better electrochemical properties and can be used as a negative electrode material.

A fast method for the synthesis of ε-Fe2O3, yielding 100% pure material with a variable FMR frequency, is proposed.

Magnetically hard ferrites attract considerable interest due to their ability to maintain a high coercivity of nanosized particles and therefore show promising applications as nanomagnets ranging from magnetic recording to biomedicine. Herein, we report an approach to prepare nonsintered single-domain nanoparticles of chromium-substituted hexaferrite via crystallization of glass in the system SrO–Fe2O3–Cr2O3–B2O3. We have observed a formation of plate-like hexaferrite nanoparticles with diameters changing from 20 to 190 nm depending on the annealing temperature. We demonstrated that chromium substitution led to a significant improvement of the coercivity, which varied from 334 to 732 kA m−1 for the smallest and the largest particles, respectively. The results provide a new strategy for producing high-coercivity ferrite nanomagnets.

Vanadium oxide-based nanomaterials have been prepared by cryochemical synthesis (CCS) and supercritical drying (SCD) in n-hexane and acetone. We have performed the first comparative analysis which demonstrates differences in the physicochemical and electrochemical properties of the products, related to the key features of the effect of the CCS and SCD approaches. The nanomaterials prepared from the same precursor using CCS and SCD (in acetone and n-hexane) have been shown to differ in phase composition and morphology. The oxidizing annealing of the resultant aerogels and cryogel at 500°C in air leads to the formation of only one phase: α-V2O5. In all cases except the aerogel prepared using SCD in n-hexane, the crystalline α-V2O5 has a higher discharge capacity in comparison with the unannealed aerogels and cryogel. The highest discharge capacity among the annealed aerogels is offered by the sample prepared using SCD in acetone (255 mAh/g), and the highest discharge capacity among the unannealed materials is offered by the sample prepared using SCD in n-hexane (280 mAh/g). The samples range in energy density from 110 to 640 Wh/kg. The highest energy density is also offered by the aerogel prepared using SCD in n-hexane.

A new route for the preparation of nickel and cobalt substituted spinel cathode materials (LiMn1.95Co0.025Ni0.025O4 and Li1.1Mn1.95Co0.025Ni0.025O4) by freeze-drying of acetate precursors followed by heat treatment was suggested in the present work. The experimental conditions for the preparation single-phase material with small particle size were optimized. Single-phase spinel was formed by low-temperature annealing at 700 °C. For discharge rate 0.2 C, the reversible capacities 109 and 112 mAh g−1 were obtained for LiMn1.95Co0.025Ni0.025O4 and Li1.1Mn1.95Co0.025Ni0.025O4, respectively. A good cycle performance and capacity retention about 90% after 30 cycles at discharge rate 0.2–4 C were observed for the materials cycled from 3 to 4.6 V vs. Li/Li+. Under the same conditions pure LiMn2O4 cathode materials represent a reversible capacity 94 mAh g−1 and a capacity retention about 80%. Two independent experimental techniques (cyclic voltammetry at different scan rates and electrochemical impedance spectroscopy) were used in order to investigate the diffusion kinetics of lithium. This study shows that the partial substitution of Mn in LiMn2O4 with small amounts of Ni and Co allows the cyclability and the performance of LiMn2O4-based cathode materials to be improved.

Nanocomposites of Li1.4Ni0.5Mn0.5O2+x and amorphous carbon were obtained by the pyrolysis of linear and cross-linked poly(vinyl alcohol) (PVA) in presence of Li1.4Ni0.5Mn0.5O2+x. In the case of linear PVA, the formation of nanostructured carbon coatings on Li1.4Ni0.5Mn0.5O2+x particles is observed, while for cross-linked PVA islands of mesoporous carbon are located on the boundaries of Li1.4Ni0.5Mn0.5O2+x particles. The presence of the carbon framework leads to a decrease of the polarization upon cycling and of the charge transfer resistance and to an increase in the apparent Li+ diffusion coefficient from 10−16 cm2·s−1 (pure Li1.4Ni0.5Mn0.5O2+x) to 10−13 cm2·s−1. The nanosized carbon coatings also reduce the deep electrochemical degradation of Li1.4Ni0.5Mn0.5O2+x during electrochemical cycling. The nanocomposite obtained by the pyrolysis of linear PVA demonstrates higher values of the apparent lithium diffusion coefficient, a higher specific capacity and lower values of charge transfer resistance, which can be related to the more uniform carbon coatings and to the significant content of sp2-hybridized carbon detected by XPS and by Raman spectroscopy.

Rhodium nanowires with an average diameter of 55nm and a length of 1.5–11μm have been prepared by electrodeposition in the pores of anodic aluminium oxide (AAO) membranes which were fabricated by two-step anodization technique. Rh/AAO nanocomposites have been investigated by the combination of instrumental and electrochemical methods. The electrochemical surface area of Rh nanowires is about one order of magnitude higher than the geometrical one that is beneficial for catalytic applications. The efficiency of both isolated Rh nanowires and Rh/AAO nanocomposites towards nitrate electrochemical reduction in acidic medium has been demonstrated. The preliminary annealing of AAO templates allows us to obtain nanocomposites that are suitable for long-term catalytic applications in aggressive medium.

Li1+xNi0.5Mn0.5O2 (x <= 0.4) powders are synthesized from coprecipitated (Ni,Mn) hydroxides with different intermediate synthesis steps and under the same conditions of final annealing. It is shown that the variation of the Li introduction temperature allows the grain size to be modified from 800 nmto 200-250 nm that could be attributed to the LiOH influence on the zonal isolation processes. The appearance of NiMn2O4 and NiMnO3 intermediates was accompanied by the enhancement of cation mixing in Li1+xNi0.5Mn0.5O2 from 4.5 to 9%. According to XPS data, the variations of synthesis conditions have no influence on the oxidation states of Ni and Mn (2+/3+ and 4+, respectively). The grain size decrease of Li1+xNi0.5Mn0.5O2 promotes the corresponding decrease in charge transfer resistance at the electrode-electrolyte boundary. Lithium diffusion coefficients calculated both from cyclic voltammetry data and from electrochemical impedance spectroscopy demonstrate the corresponding enhancement from 10 (18) to 10 (14) cm(2)s (1). The degradation of electrochemical performance of Li1+xNi0.5Mn0.5O2 during cycling can be attributed to the progressive cationic disorder in the layered LiMeO2 lattice. (C) 2014 Elsevier Ltd. All rights reserved.

The thermal stability of Li1+xNi0.5Mn0.5O2 cathode materials in contact with carbon and in the course of carbon coating by pyrolysis of various carbon precursors in argon is studied. XRD patterns of Li1+xNi0.5Mn0.5O2–carbon mixtures demonstrate the first traces of phase decomposition at 600°C while corresponding TG curves show at the significant interaction between components at T>400°C. Similar interaction of complex oxide with polyethylene glycol pyrolysis products causes the complete deterioration of the layered compound. The first stage of this deterioration is a systematic increase in cation disorder between A and B sublattices of the hexagonal ABO2 structure. However, the pyrolysis of polyvinyl alcohol at 350°C results in the formation of nanostructured carbon film. The analysis of as-obtained Li1+xNi0.5Mn0.5O2–carbon composites by Raman spectroscopy shows that the linear structure of polyvinyl alcohol promotes the domination of sp2 forms of carbon in the pyrolysis products while the thermolysis products of cross-linked polymer contain mostly sp3-carbon.

For the first time, ultradispersed cathode materials LiNi0.4Mn0.4Co0.2O2 were obtained from freeze dried precursors with different anionic composition. The thermal decomposition of freeze drying precursors was carried out at 800-950 degrees C. By using XRD and SEM techniques, it was shown that particle size, crystallinity and cation ordering of Ni2+ and Li+ ions enhance with increasing thermal treatment temperature up to 900 degrees C. It was established that LiNi0.4Mn0.4Co0.2O2 powders obtained from nitrate precursor at 900 degrees C possess the highest degree of crystallinity and cation ordering.

The specifics of electrochemical lithium intercalation into nanocrystalline ceria were studied. The lithium capacity of CeO2 − x is discovered to increase systematically as the nanoparticle size shifts down, indicating the potential of nanocrystalline ceria for use in electrochromic applications.