Fabrication of Dy2Ti2O7 nanocrystalline at 700 °C and its photocatalytic activity

Dy₂Ti₂O₇ nanocrystalline was fabricated by a soft-chemistry route named as citric acid sol–gel method (CAM). The fabricating process was monitored by XRD, FT-IR and TG-DTA methods. It was found that compared with traditional solid state reaction (SSR), Dy₂Ti₂O₇ was synthesized at a relatively low temperature (700 °C) and with shortened reaction time (2 h). The morphology and surface composition of obtained products were determined by TEM and SEM-EDX experiments. Results showed that the obtained Dy₂Ti₂O₇ with good dispersibility were all square-like; the average size was about 50 nm and there was ample oxygen-deficient (40%) on the product interfaces. Also, the obtained products had higher BET surface area (25.10 m²/g). These properties are very helpful for a catalyst to achieve excellent photocatalytic activity. Photodecomposition of methyl orange was used as the model system to evaluate its photocatalytic property. It was found that Dy₂Ti₂O₇ showed good photocatalytic activity and the decomposition rate of methyl orange was about 99% within 60 min.     

Synthesis and electrochemical properties of Li4Ti5O12

The spinel compound Li₄Ti₅O₁₂ was synthesized by a solid state method. In this synthesizing process, anatase TiO₂ and Li₂CO₃ were used as reactants. The influences of reaction temperature and calcination time on the properties of products were studied. When calcination temperature was 750 °C and calcination temperature was 24 h, the products exhibited good electrochemical properties. Its discharge capacity reached 160 mAh g⁻¹ and its capacity retention was 97% at the 50th cycle when the current rate was 1 C. When current rate increased to 10 C, its first discharge capacity could reach 136 mAh g⁻¹, and its capacity retention was 85% at the 50th cycle.     

Synthesis and luminescent properties of GdSrAl3O7:Tb phosphor under VUV/UV excitation

Superfine powder of Tb³⁺ ion-doped aluminates phosphors, GdSrAl₃O₇:Tb³⁺ was synthesized with a precursor prepared by an EDTA-sol–gel method at 900 °C. Field-emission scanning electron-microscopy (FE-SEM) observation indicated a narrow size-distribution of about 150–300 nm for the particles with elliptical shape. Upon excitation with vacuum ultraviolet (VUV) and near UV light excitation, the phosphors show a strong emission line at around 542 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺, and the highest PL intensity at 542 nm was found at a content of about 12 mol% Tb³⁺. As the Tb³⁺ concentration increases, Tb ions strongly cross-relaxation interact resulting in a decrease of the lifetime. The results reveal that GdSrAl₃O₇:Tb³⁺ would be a promising green phosphor for PDP application.     

Effects of sucrose concentration on morphology and luminescence performance of Gd2O3:Eu nanocrystals

Red Gd₂O₃:Eu nanophosphors were prepared by novel sucrose-assisted combustion method. The sucrose hydrolysis and complexing procedures were discussed by the Fourier transform infrared spectroscopy (FTIR) analysis. The effect of sucrose-to-metal ratio (S:M) on morphology and luminescence intensity of Gd₂O₃:Eu nanocrystals were investigated. And the optimum ratio was found to be S:M = 7:1, as confirmed by the results of scanning electron microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL) measurements. The highest photoluminescence emission from the particles obtained at S:M = 7:1 was about 85% of the commercial red phosphors.     

Elastic behavior of La0.67Ca0.33MnO3:ZrO2 composites

A series of Colossal Magneto Resistance materials, with compositional formula (1 − x) La_0.67Ca_0.33MnO₃ + xZrO₂ (where x = 0%, 10%, 20%, 40%, 60%, 80%) were prepared by sol–gel technique. When characterized structurally by X-ray diffraction they are found to have cubic structure. After measuring their bulk densities, the ultra sonic longitudinal (V_l) and shear velocities (V_s) were measured at room temperature using the pulse transmission technique. Using the ultrasonic data, the values of Young's and rigidity moduli along with Poisson's ratio and Debye temperatures have been calculated. As the materials are porous, zero porous elastic moduli have also been arrived at using a well-known model. The observed variation of elastic moduli with varying ZrO₂ concentration has been explained qualitatively.     

Antiferromagnetic transition in ternary rare-earth metal silicide Er5Ir4Si10 single crystal

In the present paper the electric field dependence of the permittivity of (Ba, Sr)TiO₃ ceramics is reported. Single phase Ba_1−xSr_xTiO₃ (x = 0.20 and 0.30) ceramics were obtained by powders synthesized by a modified Pechini method. The dc-tunability at room temperature is higher for the ceramic with lower strontium content as this composition is ferroelectric at room temperature, whereas the composition corresponding to the higher strontium content is paraelectric. The data are well described by the Johnson's approximation for the ferroelectric state and by an additional “extrinsic” contribution due to the polar clusters in the case of the paraelectric state (Ba, Sr)TiO₃ ceramic.     

La–Mg–Ni ternary hydrogen storage alloys with Ce2Ni7-type and Gd2Co7-type structure as negative electrodes for Ni/Mh batteries

Hydrogen strorage alloys with formula La_1.5Mg_0.5Ni₇ were prepared by induction melting followed by different annealing treatments (1073, 1123 and 1173 K) for 24 h. The alloy composition, alloy microstructure and electrochemical properties were investigated, respectively. The results showed that the multi-phase structure of as-cast alloy was converted into a double-phase structure (Gd₂Co₇-type phase and Ce₂Ni₇-type phase) through annealing treatments. Mg atoms were mainly located in Laves unit of Gd₂Co₇-type unit cell and Ce₂Ni₇-type unit cell. The electrochemical capacity of alloy electrodes after annealing treatment could be up to 390 mAh/g. The cyclic stability of alloy electrodes was significantly improved by annealing treatments; After 150 charge/discharge cycles, the capacity retention ratio of alloy annealed at 1173 K was the highest (81.9%). The high rate dischargeability of alloy electrodes was also improved due to annealing treatment.     

Structure and electrochemical properties of the Fe substituted Ti–V-based hydrogen storage alloys

To elucidate the effects of Fe on the Ti–V-based hydrogen storage electrode alloys, the Ti_0.8Zr_0.2V_2.7−xMn_0.5Cr_0.8Ni_1.0Fe_x (x = 0.0–0.5) alloys were prepared and their structures and electrochemical properties were systematically investigated. XRD results show that all the alloys consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with bcc structure. With increasing Fe content, the abundance of the C14 Laves phase gradually decreases from 43.4 wt% (x = 0.0) to 28.5 wt% (x = 0.5), on the contrary, that of the V-based solid solution phase monotonously increases from 56.6 wt% to 71.5 wt%. In addition, SEM observation finds that the grain size of the V-based solid solution phase is first gradually reduced and then enlarged with increasing x. Electrochemical investigations indicate that the substitution of Fe for V markedly improves the cycling stability and the high rate dischargeability of the alloy electrodes, but decreases the maximum discharge capacity and the activation performance. Further electrochemical impedance spectra, the linear polarization curve and the potentiostatic step discharge measurements reveal that the electrochemical kinetics of the alloy electrodes should be jointly controlled by the charge-transfer reaction rate on the alloy surface and the hydrogen diffusion rate in the bulk of the alloys. For the alloy electrodes with the lower Fe content (x = 0.0–0.2), the hydrogen diffusion in the bulk of the alloys should be the rate-determining step of its discharge process, and while x increases from 0.3 to 0.5, the charge-transfer reaction on the alloy surface becomes to the rate-determining step, which induces that the electrochemical kinetics of the alloy electrodes is firstly improved and then decreased with increasing Fe content.     

Structure and hydrogen storage properties of MgH2 catalysed with La2O3

The catalytic effect of the addition of lanthanum oxide (La₂O₃), in the range 0.5–2.0 mol%, on the hydrogen storage properties of MgH₂ prepared by ball milling has been studied. The addition of La₂O₃ reduces the formation during milling of the metastable orthorhombic γ-MgH₂ phase. The desorption rate of samples with 1 and 2 mol% La₂O₃ comes out to be about 0.010 wt% per second at 573 K under an hydrogen pressure of 0.3 bar, better than for sample with 0.5 mol% La₂O₃. The presence of LaH₃ after hydrogenation/dehydrogenation cycles has been observed in all samples. The sample with 1 mol% of La₂O₃ gives a lower hysteresis factor compared with sample with 2 mol%.     

Comparative study for mutual separation characteristics of binary mixed oxides Y2O3–Ln2O3 (Ln = Dy, Ho and Er) and Ho2O3–Er2O3 using stepwise chlorination–chemical vapor transport reaction mediated by vapor complexes KLnCl4

Mutual separation characteristics for binary oxide mixtures Y₂O₃–Dy₂O₃, Y₂O₃–Er₂O₃ and Ho₂O₃–Er₂O₃, in which these four kinds of rare earth ion(III) have very similar ion radius values, using a stepwise chlorination–chemical vapor transport (SC–CVT) reaction mediated by vapor complexes KLnCl₄ have been investigated in different temperature gradients. The unexpected results, together with that for Y₂O₃–Ho₂O₃ reported previously, are used to make a comparative analysis for the effect of ion radius values on the SC–CVT reaction for mutual separation of rare earths. Both the main deposition temperature region tendency and total transport amounts of chlorides for YCl₃ with respect to the ion radius of Y(III) were exceptional compared with those of LnCl₃ (Ln = Dy, Ho and Er), which were observed both in the degressive temperature gradient and the wave-type temperature gradient. The main deposition temperature of the chlorides produced from the oxide mixtures was in the order of DyCl₃ > YCl₃, HoCl₃ < YCl₃, ErCl₃ < YCl₃ and HoCl₃ > ErCl₃, total transported yields of the chlorides was in the order of DyCl₃ > YCl₃, HoCl₃ > YCl₃, ErCl₃ > YCl₃ and HoCl₃ > ErCl₃, and the largest separation factors 11.49 for Dy:Y, 15.28 for Ho:Y, 6.37 for Er:Y and 2.04 for Ho:Er in the lower temperature region were observed in the degressive temperature gradient, respectively. The results were discussed on the difference of ionic structure of Y on the one side and 4f lanthanoid elements of Dy, Ho and Er on the other hand, and verified that the ionic radius of the rare earth is one of the decisive factors of CVT reaction only for lanthanoid elements, not for Y. Furthermore, the improved separation factor values of 4.22 for Ho:Er and 3.20 for Er:Ho were obtained in the wave type temperature gradient due to variation of the dynamic conditions of CVT.     

Improvement of the electrochemical performance of LiMn2O4 cathode active material by lithium borosilicate (LBS) surface coating for lithium-ion batteries

The LBS coating on the surface of spinel LiMn₂O₄ powder was carried out using the solid-state method, followed by heating at 425 °C for 5 h in air. The powder X-ray diffraction pattern of the LBS-coated spinel LiMn₂O₄ showed that the LBS coating medium was not incorporated in the spinel bulk structure. The SEM result showed that the LBS coating particles were homogeneously distributed on the surface of the LiMn₂O₄ powder particles. The effect of the lithium borosilicate (LBS) coating on the charge-discharge cycling performance of spinel powder (LiMn₂O₄) was studied in the range of 3.5-4.5 V at 1C. The electrochemical results showed that LBS-coated spinel exhibited a more stable cycle performance than bare spinel. The capacity retention of LBS-coated spinel was more than 93.3% after 70 cycles at room temperature, which was maintained at 71.6% after 70 cycles at 55 °C. The improvement of electrochemical performance may be attributed to suppression of Mn²⁺ dissolution into the electrolyte via the LBS glass layer.     

Stress analysis of ceramic insulation coating on Cu/MgB2 wires for W&R MgB2 coils

Ceramic insulation coatings were produced on Cu/MgB₂ wires, which were fabricated by Hyper Tech Research Inc., using Continuous Tube Forming and Filling (CTFF) process, from the solution of Zr, and Y based organometalic compounds, solvent and chelating agent using reel-to-reel sol–gel technique for MgB₂ coils. Y₂O₃–ZrO₂/Cu/MgB₂ wires were annealed at 700 °C for 30 min with 5.8 °C/min heating rate under 4% H₂–Ar gas flow. Residual stresses were examined for Cu/MgB₂ wire and YSZ coatings with varying thicknesses. It was observed that displacement values are independent from YSZ thicknesses and the maximum effective stress value is in the Cu region. The surface morphologies and microstructure of samples were characterized using SEM. SEM micrographs of the insulation coatings revealed cracks, pinholes and mosaic structure.     

Investigation of reaction between LiNH2 and H2

The reactions for LiNH₂ under a H₂ and an Ar flow were investigated, respectively. The results showed that LiNH₂ can be converted into LiH and NH₃ by reacting with H₂ under a H₂ flow condition, whereas LiNH₂ is converted into Li₂NH and NH₃ by decomposition under an Ar flow. Moreover, the reaction between LiNH₂ and H₂ can be accelerated by mixing LiNH₂ with LiH as well as doping LiNH₂ with TiCl₃. The confirmation of reaction between LiNH₂ and H₂ is helpful for the deeper insight in the systems of Li–N–H and Li–Mg–N–H for hydrogen storage materials.     

Mn3O4 doped with nano-NaBiO3: A high capacity cathode material for alkaline secondary batteries

In this paper we report a novel Mn₃O₄ electrode doped with nano-NaBiO₃. It is demonstrated that doping with nano-NaBiO₃ alters the electrochemical inertia of Mn₃O₄, converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn₃O₄ electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn₃O₄ electrode doped with nano-NaBiO₃ can reach and become stable at 372 mAh g⁻¹ under 60 mA g⁻¹. The doped cathode can also maintain a cycling capacity of 261 mAh g⁻¹ while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g⁻¹. Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn₃O₄ cathode could possibly shorten to as little as 30 min.     

Improving the performance of hydrogen storage electrodes based on mechanically alloyed Mg61Ni30Y9

Amorphous Mg₆₁Ni₃₀Y₉ powder was produced by mechanical alloying using a Retsch planetary ball mill under liquid nitrogen cooling. Additional gentle milling with graphite powder resulted in a thin graphite coating of powder particles. Further milling with a high energy SPEX mill transferred the alloy into a fully nanocrystalline state. The morphological and microstructural changes were followed by means of XRD, SEM, TEM and DSC. Hydrogen storage electrodes based on those alloy powders were fabricated and their cathodic and anodic polarization behaviour and their charge–discharge cycling behaviour in 6 M KOH solution were investigated. It was found that the alloy modification from a non-defective amorphous to a highly defective nanocrystalline state is more effective for improving the hydrogen sorption properties of the alloy than the graphite coating, but is detrimental for the alloy passivation. Accordingly, a SPEX-milled powder electrode exhibits with C_max = 570 mAh/g a higher maximum discharge capacity than a coated Retsch-milled powder electrode with C_max = 435 mAh/g, but degrades faster during repeated cycling. Using graphite powder supporting material for electrode preparation on a nickel foam carrier was found to be much more beneficial than nickel powder for achieving maximum discharge performance.     

Zn_2SnO_4和Zn_2Sn_(0.8)Ti_(0.2)O_4/C的制备和电化学性能(英文)

以SnCl4.5H2O、TiCl4、ZnCl2和N2H4.H2O为原料,采用水热法制备Zn2Sn0.8Ti0.2O4纳米粉体。在此基础上,以葡萄糖和水热合成的Zn2Sn0.8Ti0.2O4为原料,以碳热还原法制备Zn2Sn0.8Ti0.2O4/C复合材料。利用XRD、XPS、TEM、恒电流充放电等方法分别研究Zn2SnO4和Zn2Sn0.8Ti0.2O4/C复合材料的结构、形貌和电化学性能。同时用非原位XRD、XPS和SEM分析Zn2Sn0.8Ti0.2O4/C复合材料电极在充放电过程中的结构和形貌变化。合成的纯Zn2SnO4的首次放电容量为1670.8mA.h/g,循环40次后放电容量迅速衰减为342.7mA.h/g。而Zn2Sn0.8Ti0.2O4/C复合材料的首次放电容量为1530.0mA.h/g,循环100次后容量还保持为479.1mA.h/g,与纯Zn2SnO4、Zn2Sn0.8Ti0.2O4和Zn2SnO4/C相比,电化学性能有较大的提高。     

Effects of protecting layer [Li,La]TiO3 on electrochemical properties of LiMn2O4 for lithium batteries

A sample of LiMn₂O₄ spinel oxide was surface-modified with lithium lanthanum titanate ([Li,La]TiO₃), which was developed as a lithium ionic conductor, by means of hydrothermal processing and subsequent heat treatment at 400 °C. The surface coating layers were analyzed by morphology observation using a transmission electron microscopy. Energy-dispersive spectrometry and X-ray photoelectron spectroscopy were used for element investigation. The surface modification effects on rate capability during cycling and capacity retention for the LiMn₂O₄ spinel oxide were confirmed. Then Mn dissolution during storage at elevated temperatures of the pristine, coated sample was characterized. The Mn dissolution characterization was based on the idea that Mn dissolution is one of the most significant reasons for capacity loss for LiMn₂O₄ spinel oxide, and this phenomenon is especially severe at elevated temperatures. Our experimental results indicate that the surface-modified sample shows much a better initial capacity and rate capability compared with the pristine sample. The [Li,La]TiO₃ coating effectively enhances the structural stability of LiMn₂O₄ at elevated temperatures, most likely because the [Li,La]TiO₃-modifying layers play a definitive role in suppressing Mn dissolution in the electrolyte during storage.     

Another unusual phenomenon for Zr7Ni10: structural change in hydrogen solid solution and its conditions

Zr₇Ni₁₀ has three hydrogen occlusion phases, , β and γ, and the following unusual features are known for the phase transitions in the Zr₇Ni₁₀–H₂ system: (1) The intermediate hydride phase (β) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase () exhibits a much higher hydrogen solubility during hydrogenation than during dehydrogenation. In order to clarify the mechanism about the difference in the hydrogen solubility of the phase, the relation between the pressure-composition isotherms and corresponding structural change has been examined by a conventional volumetric method and X-ray diffraction. Through the examination, we discovered that the crystal structure of the phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated phase changes from an orthorhombic structure to a tetragonal structure. The conditions causing the structural change were then examined, and it has been found that the phase maintains its original orthorhombic structure as long as it is hydrogenated so as not to absorb enough hydrogen to change it to the hydride with a higher hydrogen content (γ). The phenomenon can be understood as one of the hydrogen-assisted phase transitions such as hydrogen-induced amorphization (HIA) in the sense that the phase transition requires hydrogenation under special conditions.     

DFT studies of hydrogen storage properties of Mg0.75Ti0.25

Absorption energies of hydrogen in Mg_0.75Ti_0.25 alloys as a function of the hydrogen concentration were calculated using Density Functional Theory. Four types of structures of alloys and their hydrides including TiAl₃, ZrAl₃, AuCu₃, and segregated types of structures were considered. The stability of the configurations, and the structural and electronic bonding properties were studied. The hydrogenation properties depend highly on the structure of the alloys. The ordered alloys have very similar properties to that of pure Mg. For segregated alloys, the hydrogenation properties can be divided to Ti-like, ordered alloy-like and Mg-like from low to high hydrogen concentration. The formation energies show that for the four structures, segregated Mg_0.75Ti_0.25 is favored for alloys, whereas TiAl₃ type of Mg_0.75Ti_0.25H₂ are favored for hydrides. Therefore hydrogen induced structural rearrangement of the intermetallic structures of the Mg_0.75Ti_0.25 might occur upon hydrogen cycling. For the non-homogenous Mg-Ti-H system, further phase segregation of Ti in Mg might occur. Partial dehydrogenation with some hydrogen remaining in the Ti-rich region may improve reversibility.     

Solution processing of V2O5-WO3 composite films for enhanced Li-ion intercalation properties

We have employed a simple and novel solution processing method to prepare V₂O₅-WO₃ composite films which demonstrate enhanced Li-ion intercalation properties for applications in lithium-ion batteries or electrochromic displays. This solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods (e.g. using precursors of sodium metavanadate and sodium tungstate solution). The V₂O₅-WO₃ composite films show enhanced Li-ion intercalation properties compared to pure V₂O₅ and WO₃ films. For example, at a high current density of 1.33 A/g, V₂O₅-WO₃ film with a V₂O₅/WO₃ molar ratio of 10/1 exhibits the highest capacities of 200 mA h/g at the first cycle and 132 mA h/g after 50 cycles, while pure V₂O₅ film delivers discharge capacities of 108 mA h/g at the first cycle and 122 mA h/g after 50 cycles. The enhanced Li-ion intercalation properties of the composite films are ascribed to the reduced crystallinity, the increased porosity and thus the enhanced surface area. Both the cyclic voltammogram and chronopotentiometric curves of the V₂O₅-WO₃ film with a molar ratio of 10:1 are distinctively different from those of pure oxide films, suggesting a different Li-ion intercalation process in the V₂O₅-WO₃ film with the molar ratio of 10:1.