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1.
In this work, Ca1−xHoxMnO3 (x = 0, 0.1 and 0.2) perovskite oxide pelleted electrodes were prepared from the respective powders obtained by the citrate route method at 1173 K.The electrodes exhibit particle size that decreases with the holmium content in the oxide. All the samples reveal semiconductor behaviour and the presence of holmium induces a marked decrease in the electrical resistivity. The results can be well attributed to the changes in the Mn4+/Mn3+ ratio. Electrodes were characterized by cyclic voltammetry and chronopotentiometry. Cyclic voltammetric studies indicate a similar behaviour of the electrodes, irrespective of their composition. Two pairs of peaks were identified and associated, one to the Mn4+/Mn3+ redox couple and the other to the Mn7+/Mn4+ and Mn6+/Mn4+ redox couples. The voltammetric data provide evidence that the electrodes roughness factor increases with the introduction of Ho-ions in the oxide structure, what is consistent with the crystallite size obtained by X-ray diffraction (XRD) and the morphology observed by scanning electron microscopy (SEM). The Ho-substituted electrodes present higher current density when compared with CaMnO3 electrodes what can be attributed both to higher electrical conductivity and smaller particle size. The chronopotentiometric studies have shown that the discharge occurs by different mechanisms for the oxide electrodes with and without Ho.  相似文献   

2.
The microstructural and electrochemical properties of La2.3−xCaxMg0.7Ni9 hydrogen storage alloys have been studied systematically. The microstructure examined by XRD, SEM and EDX shows that the alloys consist of multi-phases, which are (La, Mg)2Ni7 phase, LaMgNi4 phase, (La, Mg)Ni3 phase and LaNi5 phase. It is can be found that Ca does not appear to segregate. This phenomenon is different from Mg. With increasing Ca content, the main phase varies from (La, Mg)2Ni7 phase (x = 0) to (La, Mg)Ni3 phase (x = 0.3), LaNi5 phase (x = 0.6, 0.8) and (La, Mg)Ni3 phase (x = 1.0, 1.3). The maximum discharge capacities of the alloy electrodes increase from 244.6 mAh/g (x = 0) to 380 mAh/g (x = 1.0), and then decrease to 353.6 mAh/g (x = 1.3). The discharge capacities of the alloys are related to phase content. Cell volumes of LaNi5 phase, (La, Mg)2Ni7 phase and (La, Mg)Ni3 phase all decrease and the high rate dischargeability (HRD) is improved by adding Ca. The alloy electrodes also show relative good cycling stability up to 100 cycles.  相似文献   

3.
The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La1−xCaxAl11−yzMgyTizO18 (x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage ceramic technology. By X-ray diffraction and scanning electron microscopy, predominant phase LaAl11O18 and second phases LaAlO3 and -Al2O3 are identified. Ceramic materials are characterized with high physico-mechanical properties and may be find application for production of mill bodies and materials for immobilization of nuclear waste.  相似文献   

4.
The development of interfaces with low impedance is a prerequisite for long-term neural devices. A broad range of new materials has been developed for this purpose. Here we show how the performance of traditional gold electrodes can be improved by controlling the deposition parameters of the gold film. The morphology of the film was tuned from granular to columnar structure as shown by scanning electron microscopy of film cross sections. Electrochemical characterisation with impedance spectroscopy, chronoamperometry and cyclic voltammetry demonstrates that the dense columnar structure of the films effectively lowers the impedance of the interface and increases charge injection properties. The samples produced are also compared to titanium nitride films, a well-established electrode material with a columnar structure.  相似文献   

5.
Effects of electrolyte addition on photocatalytic activity of (Ga1−xZnx)(N1−xOx) modified with either Rh2−yCryO3 or RuO2 nanoparticles as cocatalysts for overall water splitting under visible light (λ > 400 nm) are investigated. The cocatalyst Rh2−yCryO3 is confirmed to selectively promote the photoreduction of H+, while RuO2 functions as both H2 evolution sites and as efficient O2 evolution sites. The activity of Rh2−yCryO3-loaded (Ga1−xZnx)(N1−xOx) is found to be suppressed in the presence of Cl, which undergoes oxidation by photogenerated holes in the valence band of (Ga1−xZnx)(N1−xOx). Alkaline- and alkaline earth-metal cations in the reactant solution compensate the negative effect of Cl to a certain extent depending on the metal cation employed. Among the electrolytes examined, the addition of an appropriate amount of NaCl or A2SO4 (A = Li, Na, or K) to the reactant solution without pH control is found to increase activity by up to 75% compared to the case without additives. Direct splitting of seawater to produce H2 and O2 is also demonstrated using Rh2−yCryO3-loaded (Ga1−xZnx)(N1−xOx) catalyst under visible light.  相似文献   

6.
Effect of substitution of CuO and WO3 on the microwave dielectric properties of BiNbO4 ceramics and the co-firing between ceramics and copper electrode were investigated. The (Bi1−xCux)(Nb1−xWx)O4 (x = 0.005, 0.01, 0.015, 0.02) composition can be densified between 900 and 990 °C. The microwave dielectric constants lie between 36 and 45 and the pores in ceramics were found to be the main influence. The Q values changes between 1400 and 2900 with different x values and sintering temperatures while Qf values lie between 6000 and 16,000 GHz. The microwave dielectric losses, mainly affected by the grain size, pores, and the secondary phase, are discussed. The (Bi1−xCux)(Nb1−xWx)O4 ceramics and copper electrode was co-fired under N2 atmosphere at 850 °C and the EDS analysis showed no reaction between the dielectrics and copper electrodes. This result presented the (Bi1−xCux)(Nb1−xWx)O4 dielectric materials to be good candidates for LTCC applications with copper electrode.  相似文献   

7.
The binary systems ReS2–TaS2 and OsS2-TaS2 are studied. Mixed layer structure (MLS) phases are found in RexTa1−xS2 with a composition range of 0.25x0.5, as well as in the OsxTa1−xS2 with a composition range of 0.26x0.33. The MLSs of both phases are constructed by a random and mixed stacking of the 2Hb-layers and 3R-layers. The magnetic susceptibilities of samples from both phases show a weak Pauli-paramagnetism. The paramagnetic moment and the electrical conductivity of both phases decrease as the composition x increases. The behaviour of the paramagnetic moment and the electrical conductivity of those phases offer us a good example of the number of conduction electrons and their effect.  相似文献   

8.
It is known that Curie temperature of barium titanate system can be altered by the substitution of dopants into either A- or B-site. Dopants could pinch transition temperature, lower Curie temperature, and raise the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transition close to room temperature. This isovalent substitution could improve the ferroelectric properties of the BaTiO3-based system. In this study, barium zirconate titanate Ba(ZrxTi1−x)O3 (BZT; x = 0, 0.02, 0.05 and 0.08) ceramics were prepared by conventionally mixed-oxide method. The ferroelectric properties of BZT ceramics were investigated. Increasing Zr content in the BaTiO3-based compositions caused a decrease in Curie temperature (Tc). At Tc, the highest relative permittivity of BZT with an addition of 0.08 mol% of Zr was 12,780. The BZT specimens with the additions of 0.05 mol% and 0.08 mol% of Zr presented the remanent polarization at 25 μC/cm2 and 30 μC/cm2, respectively.  相似文献   

9.
Performances of BaTi1 − xNixO3 perovskites, prepared using sol–gel method, as catalysts for partial oxidation of methane to syngas have been studied. The catalysts were characterized by XRD, BET and TEM. The experimental studies showed the calcination temperature and Ni content exhibited a significant influence on catalytic activity. Among catalysts tested, the catalyst BaTi0.8Ni0.2O3 exhibited the best activity and excellent stability.  相似文献   

10.
Fe1−xCox nanowires in self-assembled arrays with varying compositions were produced by the template-assisted pulsed electrochemical deposition method. The structural and magnetic properties of the arrays were investigated using several experimental techniques. TEM analyses indicated that the nanowires were regular, uniform, 8 μm in length and 50 nm in diameter. The results of X-ray diffraction indicated that the body-centered-cubic (bcc) (α), face-centered-cubic (fcc) (γ), and hexagonal-close-packed (hcp) () Fe–Co phases appeared in different compositions. Magnetic measurements showed that the coercivity and squareness of the hysteresis loops of the Fe1−xCox changed with their compositions, which may be attributable to shape anisotropy. The room temperature 57Fe Mössbauer spectra of the arrays of the Fe1−xCox nanowires revealed strong shape anisotropy.  相似文献   

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