Investigations on selected gallium doped lanthanum chromites as electrode materials for HC detection

Perovskite-type mixed oxides with the formula La_1−xGa_0.3Cr_0.7O_3−δ (x=0.2; 0.1; 0.05; 0) were investigated in view of their usability as electrode materials in exhaust gas sensors for HC detection. The electrode materials were characterised regarding their structure, catalytic activity for propene oxidation and potentiometric behaviour in combustible gaseous mixtures. XRD-measurements indicate, that the solid oxide method does not permit lanthanum deficiencies x ≥ 0.05. The electrodes show non Nernstian behaviour. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Physico-chemical investigations on selected gallium doped lanthanum chromites

Investigations on lanthanum gallium chromium mixed oxides of the compositions La_1.0Ga_0.2Cr_0.8O_3−d and La_0.9Ga_0.2Cr_0.8O_3-d are presented regarding their structure, redox stability, conductivity and catalytic activity for the oxidation of propene. The mixed oxide has perovskite-type structure, high redox stability, an electronic p-type conductivity and low catalytic activity. If the perovskite-type compound has a deficiency of lanthanum, the electronic conductivity, surface area and catalytic activity are significantly higher. The catalytic activity is likely comparable to that of gold. Similar to gold electrodes of solid electrolytes, oxygen electrodes formed with gallium doped lanthanum chromite show a relatively high sensitivity to hydrocarbons such as propene at temperatures of about 700 °C. The mixed oxide is possibly suitable as electrode material for exhaust gas sensors using oxide-ion conducting solid electrolytes. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, September 13–20, 1998.     

Sonochemical construction of hierarchical strontium doped lanthanum trisulfide electrocatalyst: An efficient electrode for highly sensitive detection of ecological pollutant in food and water

Herbicides are used constantly in agriculture to enhance productivity across the globe. This herbicide monitoring requires utmost importance since its high dose leads to ecological imbalance and a negative impact on the environment. Moreover, a quantification of toxic herbicide is one of the important problems in the food analysis. In this work, deals with the development of a simple, and facile one-pot sonochemical synthesis of strontium doped La₂S₃ (Sr@La₂S₃). Morphological and structural characterization confirms the doping of Sr@La₂S₃ to generate a hierarchical layered structure. The electrochemical performance of modified with rotating disk electrode (RDE) using Sr@La₂S₃ composite is high, compared to La₂S₃ and bare electrodes towards the quantitative detection of mesotrione (MTO) in phosphate buffer. Sr@La₂S₃/RDE showed good sensitivity for MTO detection and it exhibit a range of 0.01–307.01 μM and limit of detection of 2.4 nM. Besides, the selectivity of fabricated electrode is high as it can electrochemically reduce MTO particularly, even in the presence of other chemicals, biological molecules and inorganic ions. The repeatability of MTO detection is high even after 30 days with a lower RSD values. Hence, simple fabrication of Sr@La₂S₃/RDE could be a novel electrode for the sensitive, selective, and reproducible determination of herbicides in real-time applications.     

Investigations on thermoelectric power of lanthanum oxide doped ferroelectric sodium vanadate

The thermoelectric power of ferroelectric sodium vanadate doped with different concentrations of lanthanum oxide has been measured in the temperature range covering their transition temperatures. It has been observed that the thermoelectric power increases with temperature, attains maximum value and with further increase in the temperature decreases to zero, indicating Curie temperature of the respective samples; however, it changes the sign for higher temperature. The thermoelectric power of sodium vanadate increases to maximum with increase in doping concentration of lanthanum oxide from 0.025 to 0.1 mol%; however, it decreases for higher concentrations. Pure as well as lanthanum oxide doped sodium vanadate samples showp-type behaviour in the ferroelectric region andn-type behaviour in the paraelectric region.     

Electrical properties of yttrium doped strontium titanate with A-site deficiency as potential anode materials for solid oxide fuel cells

Yttrium doped strontium titanate with A-site deficiency ((Y_0.08Sr_0.92)_1 ? xTiO_3 ? δ) was synthesized by conventional solid state reaction. The deficiency limit of A-site in (Y_0.08Sr_0.92)_1 ? xTiO_3 ? δ is below 6 mol% in Ar/H₂ (5%) at 1500 °C. The sinterability of (Y_0.08Sr_0.92)_1 ? xTiO_3 ? δ samples decreases slightly with increasing A-site deficiency level (x). The ionic conductivity of (Y_0.08Sr_0.92)_1 ? xTiO_3 ? δ samples increases while the electronic conductivity decreases with increasing A-site deficient amount. The defect chemistry analysis indicates that the introduction of A-site deficiency results in not only the increase of oxygen vacancy concentration but also the decrease of Ti³⁺-ion concentration. The latter plays the main role in the electrical conduction. (Y_0.08Sr_0.92)_1 ? xTiO_3 ? δ shows good thermal-cyclic performance in electrical conductivity and has an excellent chemical compatibility with YSZ electrolyte below 1500 °C.     

Investigations of a number of alternative negative electrode materials for use in lithium cells

There is a considerable interest in the replacement of graphite as the negative electrode reactant in rechargeable lithium batteries by composite electrodes containing alloys or convertible oxides. Some such materials can have much higher theoretical specific capacities than graphite, more than a factor of ten in some cases. In addition it would be desirable to eliminate the irreversible loss of capacity during the first charging cycle that is characterisitic of graphite electrodes, as well to raise the operating potential somewhat in order to reduce the danger of the formation of elemental lithium during recharging. The several strategies that have been followed in the search for attractive alternatives will be briefly described. It has been found to be difficult to obtain the desired combination of high capacity, low first cycle loss and capacity retention upon cycling. Investigations of the electrochemical behaviour of elemental boron and borides (B₄C, CaB₆, LaB₆, AlB₂, SiB₃), elemental silicon and silicides (Mg₂Si, FeSi₂, CoSi₂, NiSi₂, TiSi₂, VSi₂) and of siliconmonoxide, SiO, will be reported. The galvanostatic cycling method was used, with thick layer electrodes (30 μm) deposited upon copper foil in coffee bag-type cells with a liquid electrolyte. Lithium foil was used for the counter and reference electrodes. The results of the investigation of the morphological changes upon cycling, as observed by the use of SEM, will also be presented. Paper presented at the 7th Euroconference on Solid State Ionic, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

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用煅烧石油焦作填料、煤沥青作粘结剂和B4C、Si、Ti作添加剂，利用热压工艺制备了系列重结晶掺杂石墨，并通过化学气相反应法在掺杂石墨表面沉积了有梯度的SiC涂层。对掺杂石墨的热力学性能、微观结构及在HT-7装置的聚变环境中的行为进行了考察。结果表明：与纯石墨材料相比，掺杂了10%的B4C的重结晶石墨力学性能得到明显的改善，抗弯强度达104Mpa，但导热性能较差；掺杂了Si、Ti的重结晶石墨的热导率高，达314W•m-1•K-1，但力学性能较差；掺杂了BSTDG的石墨在聚变环境中的抗等离子体辐照能力明显提高；在HT-7装置中经过一轮实验的辐照后，SiC涂层厚度因等离子体的刻蚀由初期的40～50μm下降至5μm左右，且局部区域涂层剥落。     

A defect model for undoped and tellurium doped gallium arsenide

The introduction of two new defects, both 〈100〉 split-interstitials, can explain the experimental results obtained from annealing studies on undoped and tellurium doped gallium arsenide. This model concludes that the arsenic and gallium Frenkel reactions only occur at annealing temperatures above 4̃00 and 9̃00°C respectively and suggests that gallium diffuses by occupying split-interstitial sites. This model also suggests that interestitial arsenic may occupy the hexagonal interstitial sites.     

Synthesis and characterization of doped apatite-type lanthanum silicates for SOFC applications

A series of iron- and/or aluminium-doped apatite-type lanthanum silicates (ATLS) La_9.83Si_{6 ‐ x ‐ y}Al_xFe_yO_26 ± δ (x = 0, 0.25, 0.75, and 1.5, y = 0, 0.25, 0.75, and 1.5) were synthesized using the mechanochemical activation (MA), solid state reaction (SSR), Pechini (Pe) and sol-gel (SG) methods. The total conductivity of the prepared materials was measured under air in the temperature range 600-850 °C using 4-probe AC impedance spectroscopy. Its dependence on composition, synthesis method, sintering conditions and powder particle size was investigated. It was found that for electrolytes of the same composition, those prepared via mechanochemical activation exhibited the highest total specific conductivity, which was improved with increasing Al- and decreasing Fe-content. The highest conductivity value at 700 °C, equal to 2.04 × 10^− 2 S cm^− 1, was observed for the La_9.83Si₅Al_0.75Fe_0.25O_26 ± δ electrolyte. La_9.83Si_4.5Fe_1.5O_26 ± δ electrolyte samples synthesized using the Pechini method exhibited higher conductivity when sintered conventionally than when spark-plasma sintering (SPS) was used.     

Anchoring alpha-manganese oxide nanocrystallites on multi-walled carbon nanotubes as electrode materials for supercapacitor

The partial coverage of manganese oxide (MnO₂) particles was achieved on the surfaces of multi-walled carbon nanotubes (MWCNTs) through a facile hydrothermal process. These particles were demonstrated to be alpha-manganese dioxide (α-MnO₂) nanocrystallites, and exhibited the appearance of the whisker-shaped crystals with the length of 80–100 nm. In such a configuration, the uncovered CNTs in the nanocomposite acted as a good conductive pathway and the whisker-shaped MnO₂ nanocrystallites efficiently increased the contact of the electrolyte with the active materials. Thus, the highest specific capacitance of 550 F g⁻¹ was achieved using the resulting nanocomposites as the supercapacitor electrode. In addition, the enhancement of the capacity retention was observed, with the nanocomposite losing only 10% of the maximum capacity after 1,500 cycles.     

Investigations of cobalt and carbon codoping in gallium nitride for spintronic applications

Extensive theoretical investigations have been carried out to study the ferromagnetic properties of transition metal doped wurtzite GaN using the Tight Binding Linear Muffin-tin Orbital (TBLMTO) method within the density functional theory. The present calculation reveals ferromagnetism in cobalt doped GaN when one gallium is replaced by cobalt in a 3×3×2 supercell of GaN, which gives rise to a cobalt concentration of 2.77%. The system is half-metallic with a magnetic moment of 4.0 μ_B. When Co is bonded with one carbon, there is a drastic decrease in magnetic moment and the system becomes metallic. When Co dimer is introduced via nitrogen which corresponds to the Co concentration of 5.5% the magnetic moment is 3.99 μ_B and the system is half-metallic. Same trend is observed when Co is bonded via nitrogen with unequal distance. When cobalt dimer is formed via carbon, the moment becomes 2.95 μ_B and it shows metallic character. For dimer via carbon with unequal distance, the moment is 3.0 μ_B and the system becomes semiconductor. For higher percentage of cobalt dopant the system shows metallic character. C and Co doped GaN samples have been synthesized experimentally and characterized with X-ray diffraction, transmission electron microscopy, micro-Raman and superconducting quantum interface device measurements. The observed results are correlated with the theoretical studies.     

Nanocomposites comprised of doped cerium dioxide and lanthanum manganite for syngas production

Nanocomposites comprised of fluorite-like (Gd- or Pr-doped ceria) and perovskite-like (LaMnO_3+δ) phases were prepared using a polymerized precursor (Pechini) route. Genesis of the structure of composites with annealing temperature has been studied by X-ray diffraction, Transmission Electron Microscopy and EXAFS. Up to 1300 °C, particle sizes of both fluorite and perovskite phases remain in the nano-range. Interaction between components is reflected in the increase of doped ceria lattice parameter and disordering of Mn coordination sphere. Despite this interaction, nanocomposites possess a high conductivity along with a high lattice oxygen mobility and reactivity. The addition of CoO improves sintering of nanocomposites.     

Preparation and electrochemical characterization of cobalt-manganese oxide as electrode materials for electrochemical capacitors

Cobalt-manganese oxide materials (CMOs) were prepared by chemical method and heat treated at 150, 400, 600, 800 and 1000 °C, respectively. The physical and electrochemical properties of the materials were characterized. The heat treatment process leads to the removal of water molecules adsorbed on the surface of CMO particles (below 400 °C) and the progressive reduction of Mn and Co ions from Mn⁴⁺ and Co³⁺ to Mn³⁺/Mn²⁺ and Co²⁺, respectively (440-1000 °C). CMOs obtained by treatment below 800 °C have poor crystallinity and a highly crystallized tetragonal phase by treatment at 1000 °C. The ratio of Mn and Co in CMOs is found by EDX analysis to be about 2:1. The electrochemical testing results indicate that the high crystallization of CMO is disadvantageous for the energy storage as electrode material of electrochemical capacitors. However, for CMOs with poor crystallinity, relatively high specific capacitances can be obtained. The incorporation of protons and ions into the CMO's lattice during electrochemical charge/discharge process leads to the distortion of crystal lattice and improvement of crystallinity of CMO. The XRD patterns show that negative electrode (NE) and positive electrode (PE) have tetragonal (Co, Mn)(Mn, Co)₂O₄ phase.     

氮掺杂碳气凝胶电极材料的制备及性能

以三聚氰胺（M）、间苯二酚（R）和甲醛（F）为原料,经溶胶-凝胶法、超临界干燥和高温碳化制备了系列的氮掺杂碳气凝胶（NCAs）。X射线光电子能谱(XPS)分析表明,氮元素成功地引入到碳气凝胶中,并且可以通过调节三聚氰胺掺杂量来控制氮掺杂量;扫描电子显微镜（SEM）和N2吸附测试显示出不同氮掺杂量的碳气凝胶的微观结构差异较大,随着氮含量的增加,比表面积有先减后增的趋势;在6 mol/L KOH溶液中进行的恒流充放电和循环伏安测试表明,引入氮元素能够极大地改善碳气凝胶的电化学性能,最高比电容量达176 Fg-1,并且凝胶具有良好的电容特性和可逆性。     

A ceria layer as diffusion barrier between LAMOX and lanthanum strontium cobalt ferrite along with the impedance analysis

A thin interlayer of samarium doped ceria (SDC) is applied as diffusion barrier between La_1 ? xSr_xCo_yFe_1 ? yO₃ x = 0.1–0.4, y = 0.2–0.8 (LSCF) cathode and La_1.8Dy_0.2Mo_1.6W_0.4O₉ (LDMW82) electrolyte to obstruct Mo–Sr diffusion and solid state reaction in the intermediate temperature range of SOFC. We demonstrate the effectiveness of the diffusion barrier through contrasting the clearly defined interfaces of LSCF/SDC/LDMW82 against a rugged growing product layer of LSCF/LDMW82 in 800 °C thermal annealing, and analyze the product composition and the probable new phase. In addition, the measured polarization resistance is considerably lower for the half-cell with a diffusion barrier. Therefore, the electrochemical performance of the LSCF cathode is investigated on the SDC-protected LDMW82. The cell with LSCF (x = 0.4) persistently outperforms the one with x = 0.2 in polarization resistance because of its small low-frequency contribution. The activation energy of polarization resistance is also lower for La_0.6Sr_0.4Co_yFe_1 ? yO₃ (112–135 kJ/mol), than that for La_0.8Sr_0.2Co_yFe_1 ? yO₃ (156–164 kJ/mol). La_0.6Sr_0.4Co_yFe_1 ? yO₃ y = 0.4–0.8 is the proper composition for the cathode interfaced to SDC/LDMW82.     

New layered metal oxides as positive electrode materials for room-temperature sodium-ion batteries

In order to achieve better Na storage performance, most layered oxide positive electrode materials contain toxic and expensive transition metals Ni and/or Co, which are also widely used for lithium-ion batteries. Here we report a new quaternary layered oxide consisting of Cu, Fe, Mn, and Ti transition metals with O3-type oxygen stacking as a positive electrode for room-temperature sodium-ion batteries. The material can be simply prepared by a high-temperature solidstate reaction route and delivers a reversible capacity of 94 m Ah/g with an average storage voltage of 3.2 V. This paves the way for cheaper and non-toxic batteries with high Na storage performance.     

Effect of nickel catalyst on physicochemical properties of carbon xerogels as electrode materials for supercapacitor

Carbon xerogels and Ni-doped carbon xerogels prepared by the sol-gel polymerization were examined to reveal the effect of metallic nickel incorporated in carbon matrix on the physicochemical properties of carbon xerogels and their electrochemical performance for supercapacitor electrode in aqueous 6 M KOH solution. As shown by XRD and XPS measurements, the decomposition of nickel precursor in carbon matrix led to the creation of well-crystalline particles of metallic nickel which gave rise to the changes in the morphology, chemical and porous structure of carbon xerogels. Due to the modification of porous structure the surface area increased from 595 m²/g via 632 m²/g up to 660 m²/g for carbon xerogel, 7 wt% and 10 wt% Ni-doped composites, respectively. The enhancement of the surface area occurred along with diminishing the BJH average pore diameter. The value for nickel free xerogel amounted to 11.35 nm, whereas the value of 5.71 nm was measured for 10 wt% Ni xerogel. The changes in the porous and chemical structure created during the formation of carbon-nickel composites as well as the pseudo-capacitive effects arising from the redox reaction of nickel particles present in carbon matrix brought about a significant improvement of electrode capacitance. Electrochemical measurements showed that in comparison with capacitances measured for nickel free electrode (82.1 F/g calculated using the cyclic voltammetry and 88.8 F/g calculated using the galvanostatic charge/discharge method), the respective capacitances for 10 wt% Ni-doped carbon xerogel increased up to 103.0 F/g and 103.4 F/g. These values correspond to 25 and 16% improvement, respectively.     

半绝缘GaAs的欧姆接触电极材料Ag/Co掺杂的非晶碳膜制备与检测

稳定的欧姆接触对半导体器件的正常工作起到至关重要的作用.目前市场上主要采用金/金锗镍合金作为n型GaAs的电极材料,工艺复杂,成本高昂.本文研究了一种新型的、廉价的适用于半绝缘GaAs的欧姆接触电极材料Ag/Co掺杂的非晶碳膜及其制备过程,以便于读者对半导体器件的制备工艺和流程有所了解.     

Mixed conductive electrode materials for sensors and SOFC

Modified active electrode materials based upon rare earth manganites were developed for different solid electrolyte electrochemical cells. The preparation, structure, thermal expansion, the state of oxygen on the surface, the electronic and ionic conductivity of the perovskites Ln_1−xCa(Sr)_xMn_1−y(Co, Ni)_yO_3−δ with various compositions and electrode kinetics on the manganite electrode/solid electrolyte interfaces were investigated. The value of the bulk conductivity was larger than 150 S/cm (at 1100 K) and increased significantly with increasing contents of Ni or Co. The thermal expansion coefficients of rare earth manganites were close to those of ZrO₂ based solid electrolytes. The expansion coefficients of Co or Ni subsituted lanthanum manganites increase with Co or Ni substitution and are over 12•10⁻⁶K⁻¹. The ionic conductivities were determined using encapsulated zirconia microelectrodes based on a Hebb-Wagner analysis of the currentvoltage curves. The relatively high oxide ion conductivity of 10⁻⁵ S/cm at 900...1000 K was found by Ni or Co doped manganites. Studies of the electrode kinetics using complex impedance spectroscopy show that Co and Ni doped manganites have advantages if used as electrodes as compared with these for noble metals. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994