XAS characterization of the RuO2–Ta2O5 system local (crystal) structure

The influence of the preparation method on the structural properties of the RuO₂–Ta₂O₅ system was investigated. Both thin films on Ti substrates and powder samples of nominal composition Ti/RuO₂–Ta₂O₅ (Ru:Ta = 100:0, 90:10, 80:20, 30:70, and 0:100 at.%) were prepared through thermal decomposition of polymeric precursors (DPP). The thin films and powder samples were investigated using X-ray absorption spectroscopy (XAS). XANES analyses showed that Ru and Ta are present in the Ru(IV) and Ta(V) oxidation states. EXAFS signals of all the samples were analyzed, to obtain the average bond length (r), coordination number, and the Debye–Waller factor (σ²) for each Ru–O, Ru–Ru, Ta–O nearest-neighbor. The first shell Ru–O distance was found at 1.91–1.92 Å with coordination number of 1.8–2.1, and at 2.01–2.02 Å with coordination number of 3.9–4.1. The Ta–O distance obtained for all the samples and in both modes (transmission and fluorescence) had significantly different values from the theoretical ones. The results revealed that the local structure around both the Ru and Ta sites are similar, and that they consist of distorted M–O₆ octahedra (where M = Ru or Ta).     

Glasses and glass-ceramics in the SrO–TiO2–Al2O3–SiO2–B2O3 system and the effect of P2O5 additions

The glass formation abilities of various compositions in SrO–TiO₂–Al₂O₃–SiO₂, SrO–TiO₂–B₂O₃–SiO₂, SrO–TiO₂–Al₂O₃–B₂O₃, and SrO–TiO₂–Al₂O₃–SiO₂–B₂O₃ systems were studied. Many new compositions were found to be suitable for the casting of crack-free, optically clear glasses of different color and with glass transition temperatures ranging from 595 to 775 °C. The crystallization behavior, structure, and thermal expansion behavior of selected glasses were analyzed by DTA, XRD, dilatometry, and heat treatment. The effect of P₂O₅ on the glass structure and crystallization behavior was also studied. P₂O₅ played a dual role depending on composition. In some glasses it acted as a nucleating agent while in others it suppressed crystallization. Heat treatment of borate and borosilicate glasses transformed them into glass-ceramics while comparable SrO–TiO₂–Al₂O₃–SiO₂ glasses showed a lower tendency to crystallize and form glass-ceramics under the same conditions.     

激光辐照制备高介电常数Ta2O5陶瓷

采用大功率CO2激光辐照制备高介电常数Ta2O5陶瓷,讨论了激光制备工艺参数如激光光束模式、功率密度、扫描速率、辐照时间、辐照方式等对制备材料介电性能和组织形貌的影响,分析了其作用机理.     

RuO2-TiO2/Ti阳极的研究进展

钌系涂层钛阳极具有稳定性好、电催化活性高、环境友好等特点,在电解水、阴极保护以及电化学除垢等领域具有广泛的应用前景。其中,涂层中二氧化钌(RuO₂)的比例与存在形态是决定其电催化活性和稳定性的关键。在涂层钛阳极的制备中,热分解法因其操作简单、成本低、易工业化生产等优势而被广泛使用。介绍了目前在电解行业广泛应用的钌系涂层钛阳极——RuO₂-TiO₂/Ti阳极的应用领域,简述了RuO₂-TiO₂/Ti阳极中钌钛氧化物的特点和作用,并对RuO₂-TiO₂/Ti阳极的失效原因和制备工艺进行了阐述。主要综述了前处理、涂液组分比例、涂液浓度和烧结温度等工艺参数对通过热分解法制备的钛电极稳定性和电催化活性的影响,以及针对RuO₂-TiO₂/Ti阳极的失效原因提出钛阳极未来的改进方向,旨在促进本领域研究者更深入地了解钌钛阳极的特点、失效原因以及如何制备性能优良的涂层钛电极。     

Low-Magnetoresistance RuO2–Al2O3 Thin-Film Thermometer and its Application

Thermometers consisting of RuO₂–Al₂O₃ composite thin films were prepared by RF sputtering. It was found that different electrode-patterning techniques have dissimilar effects on the magnetoresistance (MR) and the temperature coefficient of resistance (TCR). In general, the thermometers with electrodes fabricated by photo-resist lithography exhibit superior performance compared to those with electrodes prepared using a metal mask. By adjusting the relative compositions of RuO₂ and Al₂O₃, the thermometers can be applied to a wide temperature range from 60 mK to 500 K. In a pulsed magnetic field up to 55 T, the MR at 4.2 K of a typical thermometer for the temperature range from 1.4 K to 300 K increases linearly with magnetic field to a maximum of ~15 %, corresponding to a temperature deviation of ~−4 %. As frequency increases from dc to 1.9 MHz, the MR decreases from  −13 % to ~ − 0.5 % at T = 1.3 K and H = 55 T. By integrating the thermometer with a heater on a sapphire chip, a micro-calorimeter can be developed and successfully used to measure the heat capacity of small mg-sized sample. The RuO₂–Al₂O₃ composite film can also be employed as an infrared bolometer operated at room temperature.     

Solution-combustion synthesis of ε-MnO2 for supercapacitors

ε-MnO₂ nanoparticles were synthesized through a single step solution combustion process without using any template or surfactants. Plate-like ε-MnO₂ materials, 50-150 nm in diameter and 20-25 nm in thickness, were obtained at a higher Mn(NO₃)₂:C₂H₅NO₂ molar ratio (i.e., 2:1), whereas spherical ε-MnO₂ particles (about 60 nm in diameter) were obtained as the Mn(NO₃)₂:C₂H₅NO₂ ratio is lower (e.g., 1:2). Electrochemical performance of the as-prepared ε-MnO₂ nanoparticles was examined. The spherical ε-MnO₂ nanoparticle sample shows a relatively higher specific capacitance of 123 F g^− 1 at the current density of 1 A g^− 1 in 1 M NaSO₄ electrolyte solution, probably due to its porous structures and higher surface areas in comparison with the plate-like counterparties.     

Investigation on the phase stability,sintering and thermal conductivity of Sc2O3–Y2O3–ZrO2 for thermal barrier coating application

Rare earth oxides co-doped zirconia have been developed for application in thermal barrier coating systems to promote the performance and durability of gas turbines. 8 mol%Sc₂O₃, 0.6 mol%Y₂O₃–stabilized ZrO₂ (ScYSZ) powder was synthesized by chemical co-precipitation method. The phase stability, sintering resistance and thermo-physical properties of ScYSZ and 8 wt%Y₂O₃ stabilized ZrO₂ (8YSZ) were investigated. The results indicated that both ScYSZ and 8YSZ show single tetragonal phase before heat treatment. After heat treating at 1500 °C for 300 h, ScYSZ exhibits excellent phase stability with 100% metastable tetragonal (t′) phase, whereas the content of monoclinic phase in 8YSZ reached 49.4 mol%. ScYSZ also exhibits higher sintering resistance and lower thermal conductivity than 8YSZ. ScYSZ can be considered to be explored as candidate material for TBC application.     

Structure of Mechanochemical Reaction Products in the Systems CdO(HgO)–Sb2O5(Sb2O3)

The mechanochemical reactions induced in 2CdO(HgO) + Sb₂O₅(Sb₂O₃) oxide mixtures by high-energy ball milling were studied by x-ray diffraction. New pyrochlore and fluorite phases were found to be formed at a high rate. Using thermal analysis, the temperature ranges of the structural and chemical transformations in the reaction products were determined and their compositions were refined. The synthesized materials are characterized by disordered structures, intermediate valence states, high vacancy concentrations, and deficit of the harder component, in line with the earlier proposed model for the reaction zone. The relatively high thermal stability of the metastable compounds suggests that mechanochemical ceramic processing can be used to fabricate unique ceramic materials and nanocomposites.     

Highlighting of structural units of B2O3–Li2O–P2O5 system under heat treatment

As technology evolves towards the design of small size – high efficiency devices there is a necessity for the development of solid, stable electrolytes that can be fabricated in various shapes. Accordingly, a glass system of xB₂O₃·0.4Li₂O·(0.6 − x)P₂O₅ with 0 ≤ x ≤ 0.6 mol%, was prepared by melting the raw materials at 1200 °C and rapidly cooling the melts at room temperature. The samples were afterwards heat treated to develop crystalline structures, for better identification of the units that build up the network.     

Giant electrical conductivity enhancement in BaO–V2O5–Bi2O3 glass by nanocrystallization

The effects of the annealing of 20BaO–30V₂O₅–50Bi₂O₃ glass on the structural and electrical properties were studied by scanning electron micrographs (SEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC) density (d) and dc conductivity (σ). The XRD and SEM observations have shown that the sample under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after nanocrystallization at crystallization temperature (T_c) for 1 h and to colossal crystallization after the annealing at the same temperature for 24 h. The average size of these grains after nanocrystallization at T_c for 1 h was estimated to be about 25–35 nm. However, the glass heat treated at T_c = 580 °C for 24 h the microstructure changes considerably. The nanomaterials obtained by nanocrystallization at T_c for 1 h exhibit giant improvement of electrical conductivity up to four order of magnitude and better thermal stability than the as-received glass. The major role in the conductivity enhancement of this nanomaterial is played by the developed interfacial regions “conduction tissue” between crystalline and amorphous phases, in which the concentration of V⁴⁺–V⁵⁺ pairs responsible for electron hopping is higher than inside the glassy matrix. The annealing at T_c for 24 h leads to decrease of the electronic conductivity. This phenomena lead to disappearance of the abovementioned “conduction tissue” for electrons and substantial reduction of electronic conductivity. The high temperature (above θ/2) dependence of conductivity could be qualitatively explained by the small polaron hopping (SPH) model. The physical parameters obtained from the best fits of this model are found reasonable and consistent with the glass compositions.     

Crystallization and magnetic properties of a 10Li2O–9MnO2–16Fe2O3–25CaO–5P2O5–35SiO2 glass

The crystallization behavior and magnetic properties of 10Li₂O–9MnO₂–16Fe₂O₃–25CaO–5P₂O₅–35SiO₂ (10LFS) glass have been studied using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) to observe the crystallization behavior and a superconducting quantum interference device (SQUID) for measurements of the magnetic properties. The DTA shows that the 10LFS glass has one broad exothermic peak at approximately 674 °C and one sharp (the highest) exothermic peak at 764 °C. When the 10LFS glass crystallized at 850 °C for 4 h, the crystalline phases identified by XRD were lithium silicate (Li₂SiO₃), β-wollastonite (β-CaSiO₃), lithium orthophosphate (Li₃PO₄), magnetite (FeFe₂O₄) and triphylite (Li(Mn_0.5Fe_0.5)PO₄). The SEM surface analysis revealed that the β-wollastonite and lithium silicate have a lath morphology. The TEM microstructure examination showed that the largest FeFe₂O₃ particles have a size of approximately 0.3 μm. When the 10LFS glass was heat treated at 850 °C for 16 h and a magnetic field of 1000 Oe was applied, a very small remnant magnetic induction of 0.01 emu g⁻¹ and a coercive force of 50 Oe were obtained, which revealed an inverse spinel structure.     

IrO2-Ta2O5/Ti阳极的研究进展

综述了金属氧化物涂层电极的发展现状,介绍了目前析氧领域广泛应用的铱系涂层钛电极———IrO2-Ta2O5/Ti涂层电极的特点,指出了制备过程中影响IrO2-Ta2O5/Ti涂层电极性能的因素,介绍了IrO2-Ta2O5/Ti涂层电极的改进方法,并对IrO2-Ta2O5/Ti涂层电极今后的发展方向作了展望。     

Effects of copper and Al2O3 particles on characteristics of Cu–Al2O3 composites

High-energy milling was used for production of Cu–Al₂O₃ composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al₂O₃ powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al₂O₃ particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al₂O₃ particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al₂O₃ particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al₂O₃ composites.     

Structure and electrical conductivity relaxation studies of Nb2O5-doped B2O3–Bi2O3–LiF glasses

Glasses with composition (70 − x) B₂O₃·15Bi₂O₃·15LiF·xNb₂O₅ with x = 0–1.0 mol% were prepared by conventional glass-melting technique. The molar volume V _m values decrease and the glass transition temperatures T _g increase with increase of Nb₂O₅ content up to 0.2 mol%, which indicates that Nb⁵⁺ ions act as a glass former. Beyond 0.2 mol% Nb₂O₅ the V _m increases and the T _g decreases, which suggests that Nb⁵⁺ ions act as a glass modifier. The FTIR spectra suggest that Nb⁵⁺ ions are incorporated into the glass network as NbO₆ octahedra, substituting BO₄ groups. The temperature dependence of the dc conductivity follows the Greaves variable range hopping model below 454 K, and follows the small polaron hopping model at temperatures >454 K. σ _dc, σ _ac conductivity and dielectric constant (ε) decrease and activation energy for dc conduction ΔE _dc which increases with increasing Nb₂O₅ content up to 0.2 mol%, whereas σ _dc, σ _ac and (ε) increase and ΔE _dc decreases with increasing Nb₂O₅ content beyond 0.2 mol%. The impedance spectroscopy shows a single semicircle or arcs which indicate only the ionic conduction mechanism. The electric modulus formalism indicates that the conductivity relaxation is occurring at different frequencies exhibit temperature-independent dynamical process. The (FWHM) of the normalized modulus increases with increase in Nb₂O₅ content suggesting that the distribution of relaxation times is associated with the charge carriers Li⁺ or F⁻ ions in the glass network.     

退火温度对Ta2O5薄膜光学和表面特性的影响

针对退火温度影响Ta₂O₅薄膜的光学和表面特性的问题,采用电子束蒸发技术在石英基底上制备了该薄膜,并将薄膜样品分别在200℃、400℃和600℃下进行退火。利用光谱仪测试了薄膜的透射率并反演计算得到薄膜的折射率和消光系数的变化规律,采用X射线衍射仪和原子力显微镜表征了薄膜的表面性能。研究表明,薄膜透射率曲线的峰值随退火温度升高而显著提升。随着退火温度升高,薄膜的折射率和消光系数均逐渐变大,表面粗糙度呈现下降的趋势,表面变得致密。退火前后薄膜均为非晶态。该研究为进一步提高Ta₂O₅薄膜的性能提供了试验数据。     

Fabrication of nanostructured α-Fe2O3 electrodes using ferrocene for solar hydrogen generation

Nanostructured thin films of α-Fe₂O₃ were prepared through atmospheric chemical vapour deposition (APCVD) using ferrocene and iron pentacarbonyl as precursors. Higher optical absorption was observed for hematite films prepared using ferrocene, which was attributed to the higher packing density. Photoelectrochemical (PEC) studies of the films prepared using ferrocene showed superior performance to that of iron pentacarbonyl. Photocurrent density of 540 µA/cm² and 1.5 µA/cm² at 1.23 V_RHE was achieved for hematite films prepared using ferrocene and iron pentacarbonyl, respectively. Our findings suggest that ferrocene can be used as a promising alternative to iron pentacarbonyl to prepare hematite photoelectrodes using APCVD.     

Physico-chemical and electrochemical characterization of Ti/RhOx–IrO2 electrodes using sol–gel technology

Sol–gel technology has been successfully used for the incorporation of RhO_x–IrO₂ on a Ti substrate. RhO_x–IrO₂ was prepared from chloride precursors of Rh and Ir, for surface studies. These metal oxides were then immobilised on solid Ti substrates via dip withdrawal coating methods to form thin films. The Ti/RhO_x–IrO₂ thin films were extensively characterized in terms of surface characterization and chemical composition and used in the oxidation of phenol. Thermo-gravimetric analysis (TGA) determined the calcination temperature at 700 °C where no further structural changes occurred due to mass loss. The rhodium oxide showed two-phase formations, RhO₂ and Rh₂O₃, which were attributed to high calcinated temperatures compare to one phase IrO₂ which was stable at lower temperatures. The scanning electron microscopy (SEM) showed that the morphology of the film was found to be rough with a grain-like appearance in the 150-nm range. The phase composition of these metal oxides was determined by X-ray diffraction (XRD) technique and found to have crystalline structures. The results obtained from Rutherford backscattering spectrometry (RBS) revealed information regarding the chemical composition of the metal oxides and confirmed the diffusion of Rh and Ir into the Ti substrate. Electrochemical characterization of the Ti/RhO_x–IrO₂ electrode, via cyclic voltammetry (CV), showed distinctive redox peaks: anodic and cathodic peaks associated with the oxidation and reduction of the ferricyanide–ferrocyanide couple was seen at 250 and 100 mV respectively; the peak observed at 1000 mV was associated with oxygen evolution and a broad reductive wave at −600 mV can be ascribed to the Ti/RuO_x–IrO₂ reduction, which proved that the Ti/RhO_x–IrO₂ electrode were electroactive and exhibit fast electrochemistry.     

Preparation and characterization of Y2O3–Sm2O3 co-doped ceria electrolyte for IT-SOFCs

Y₂O₃–Sm₂O₃ co-doped ceria (YSDC) powder was synthesized by a gel-casting method using Ce(NO₃)₃·6H₂O, Sm₂O₃ and Y₂O₃ as raw materials. Phase structure of the synthesized powders was characterized by X-Ray diffraction analysis. Sinterability of the powders was investigated by testing the relative density and observing the microstructure of the sintered YSDC samples. Electrical conductivity of the sintered YSDC samples was measured using impedance spectra method. Single solid oxide fuel cells based on the YSDC electrolyte were also assembled and tested. The results showed that YSDC powders with single-phase fluorite structure can be obtained by calcining the dried gelcasts at temperature above 800 °C. Average particle size of the YSDC powder is 50–100 nm. Relative density of more than 95% of the theoretical can be achieved by sintering the YSDC compacts at temperature above 1400 °C. The sintered YSDC sample has an ionic conductivity of 4.74 × 10⁻² S cm⁻¹ at 800 °C in air. Single fuel cells based on the YSDC electrolyte with 50 μm in thickness were tested using humidified hydrogen as fuel and air as oxidant, and maximum power densities of about 190 and 112 mW cm⁻² were achieved at 700 and 600 °C, respectively.