Synthesis of carbon nanotubes on La0.6Sr0.4CoO3 as substrate

A carbon nanotube/perovskite composite material was developed as material for air electrodes in fuel cells or zinc-air batteries. For this purpose, carbon nanotubes were directly grown on the perovskite La_0.6Sr_0.4CoO₃ impregnated with Fe solution which acted as substrate. The synthesis was carried out in a fluidised bed reactor. The carbon source was acetylene. The influence of the temperature on the growth of carbon nanotubes and on the stability of the perovskite was investigated. All samples contained multi-wall carbon nanotubes; however, at a temperature above 675 °C the perovskite was reduced by hydrogen originating from acetylene. The samples with the intact perovskite were further processed to air electrodes to catalyze the oxygen reduction reaction. These electrodes showed an improved performance compared to electrodes made of acetylene black and perovskites.     

Bi掺杂Ba0.6Sr0.4TiO3陶瓷的研究

本文采用传统的陶瓷工艺合成了Ba0.6Sr0.4TiO3陶瓷,研究了Bi掺杂对材料参数ε、tanδ和E的影响,并探讨了相关的掺杂改性机理。结果表明：适量的Bi能够改善陶瓷的介电性能,同时细化陶瓷的晶粒尺寸。     

A study of V-shaped PTC behaviour of Sr0.4Pb0.6TiO3 ceramics

Yttrium-doped Sr_0.4Pb_0.6TiO₃ ceramics were prepared at relatively low sintering temperature using conventional sintering technology. The sintered ceramics exhibit novel NTC–PTC composite effects. The influences of doping PbO and SiO₂ on the properties of Sr_0.4Pb_0.6TiO₃ ceramics were compared. It was found that suitable PbO additives reduce the room-temperature resistivities (ρ_RT) of Sr_0.4Pb_0.6TiO₃ ceramics and weaken their NTC effects, but the effect of doping SiO₂ is reverse. The XRD analyses show that SiO₂ additives can cause Pb²⁺ ions segregating out from Sr_0.4Pb_0.6TiO₃ lattices and form PbO·SiO₂ phase. It is estimated that the strong NTC effects of Sr_0.4Pb_0.6TiO₃ ceramics should be closely related to the Pb²⁺ immigration. The domain structure, morphology and compositional distribution of Y-doped Sr_0.4Pb_0.6TiO₃ ceramics were investigated using TEM, SEM and EDAX respectively. The results of EDAX indicate that the Pb/Sr ratio on the grain boundaries is slightly lower than that in the grains. According to the results, the V-shaped PTC behaviors of (Sr,Pb)TiO₃ ceramics are discussed.     

Microstructure and microwave-frequency electromagnetic properties of Ni0.4Zn0.6Fe2O4/Ba0.6Sr0.4TiO3 composites

(x)Ni_0.4Zn_0.6Fe₂O₄+(1−x)Ba_0.6Sr_0.4TiO₃ composite ceramics with x=0.6, 0.7, 0.8, 0.9 and 1 were synthesized by solid state reaction method. The high dense composites have only two phases, i.e., Ni_0.4Zn_0.6Fe₂O₄ and Ba_0.6Sr_0.4TiO₃. The permittivity ε′ of the composites decreases slightly with the frequency increasing from 3 MHz to 1 GHz. The permittivity ε′′ of the composites also shows a little increase with frequency in the 3 MHz–1 GHz range. The permeability displays a relaxation resonance within the 3 MHz–1 GHz frequency range. The permeability μ′ increases while the cut-off frequency decreases with the Ni_0.4Zn_0.6Fe₂O₄ concentration, obeying the Snoek's law μ_if_r=constant. The permittivity ε′ of the composites decreases with Ni_0.4Zn_0.6Fe₂O₄ concentration. The composites have a relatively higher ε′ than the pure Ni_0.4Zn_0.6Fe₂O₄ at 1–10 GHz. In the frequency range of 1–10 GHz, the magnetic permeability μ′ reaches its maximum and μ′′ shows a minimum for the composite with x=0.6 in all ceramics. The permeability μ′ of the composites decreases with dc magnetic field at 1–10 GHz. The permeability shows a domain wall resonance, and the resonance frequency shifts to high frequency with the dc magnetic field. The permittivity was also influenced by the dc magnetic field due to a magnetodielectric effect.     

Ba0.6Sr0.4TiO3-Mg2TiO4复合陶瓷材料的介电可调性及微波特性

采用常规的陶瓷工艺方法制备了Ba0.6Sr0.4TiO3-Mg2TiO4(BST-MT)复合陶瓷材料,并对其相结构、介电以及可调性和微波特性进行了研究.X射线衍射和介电温度特性测试结果表明,BST-MT复合陶瓷具有BST和MT两相结构,非铁电相MT的增加降低了其铁电性,使其介电常数和介电损耗减小.介电偏压和微波性能测试结果表明,BST-MT复合材料仍能保持较高的可调性,且微波性能得到了明显改善.样品30%BST-70%MT(质量分数)在10 kHz下的介电常数为78,介电损耗为0.000 6,在外加3 kV/mm偏置电场作用下,可调性达到25%,在3.714 GHz频率下的介电损耗为0.0145.     

EDTA-柠檬酸复合络合法制备阴极材料La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3粉体

本文采用EDTA-柠檬酸复合络合法制备了SOFC阴极La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3纳米粉体。并分别通过SEM、TEM、XRD及电化学极化阻抗仪对La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3粉体形貌、尺寸、晶相及电化学性能进行了表征。实验结果表明:采用EDTA-柠檬酸复合络合法获得的干凝胶,经800℃煅烧后可获得粒径为20~30 nm、结晶度高的钙钛矿结构的La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3纳米粉体。以La_(0.4)Sr_(0.6)Co_(0.4)Fe_(0.6)O_3粉体及添加20wt%的GDC粉体制备成的复合阴极在700℃下的极化阻抗为0.15Ω·cm~2、电导率为715 S·cm~(-1)。     

Effects of raw materials on nonhydrolytic sol-gel synthesis of Ba0.6Sr0.4TiO3

The effects of raw materials on the nonhydrolytic sol-gel synthesis of Ba_0.6Sr_0.4TiO₃ were systematically studied in this work. The samples were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM). Ba(CH₃COO)₂, Sr(CH₃COO)₂, BaCO₃ and SrCO₃ can undergo deesterification substitution reaction with Ti(OC₄H₉)₄ to synthesize Ba_0.6Sr_0.4TiO₃ phase. Sample taking Ba(CH₃COO)₂ and Sr(CH₃COO)₂ as barium and strontium source has better Ba_0.6Sr_0.4TiO₃ synthesis results than that of samples using BaCO₃ or SrCO₃. Ba_0.6Sr_0.4TiO₃ phase can not be synthesized at low temperature taking BaCl₂, SrCl₂ and TiOSO₄ as barium, strontium or titanium source due to their strong ionic bonding. TiCl₄ undergoes an alcoholysis reaction with (oxygen donor) alcohol to form a multimolecular association structure and solvated complex chlorotitanium alkoxide, which reduces the possibility of a deesterification polycondensation reaction. The Ba_0.6Sr_0.4TiO₃ phase cannot be synthesized at low temperatures when CH₃CH₂OH or C₃H₇OH is used as the solvent. The synthesis of Ba_0.6Sr_0.4TiO₃ is insufficient because of the coordination ability and solvation effect when CH₃COOH is used as the solvent. The synthesis of Ba_0.6Sr_0.4TiO₃ is the best when Ba(CH₃COO)₂, Sr(CH₃COO)₂, Ti(OC₄H₉)₄ and glycerol (C₃H₈O₃) are used as the barium source, strontium source, titanium source and solvent, respectively. Pure Ba_0.6Sr_0.4TiO₃ phase with a particle size of 17–43 nm and high dispersion is synthesized when the molar ratio of barium-strontium-titanium is 0.6:0.4:1.2.     

溶胶-凝胶法合成Ba0.6Sr0.4TiO3/MgO及介电性能研究

采用溶胶-凝胶法合成了Ba_(0.6)Sr_(0.4)TiO_3/MgO复合粉体,研究了烧结温度和合成工艺对陶瓷样品介电性能的影响。研究结果表明,经650℃热处理即可得到颗粒细小均匀的超细Ba_(0.6)Sr_(0.4)TiO_3/MgO粉体,平均粒径在200 nm左右。烧结温度对陶瓷样品的介电生能有明显的影响,1300℃烧结的陶瓷样品具有优良的性能。与二步合成工艺相比,一步合成工艺制备的陶瓷样品具有更好的介(?)性能。     

On the synthesis and stability of La0.6Sr0.4Ga0.3Fe0.7O3

La_0.6Sr_0.4Ga_0.3Fe_0.7O₃ is a MIEC perovskite with great chemical and thermal stability, considered a promising material for oxygen separation dense membranes and as an electrode in SOFCs. An easy, economic and scalable wet chemistry synthesis of La_0.6Sr_0.4Ga_0.3Fe_0.7O₃ (LSGF) was studied step by step, investigating and optimizing the most important aspects and parameters of the procedure (chemicals, pH, calcination temperature…). The obtained powders were carefully characterized with XRD, XPS, SEM/EDX and TPR. Once optimized the synthesis procedure, the stability in reducing condition and the reversibility of changes were tested submitting the samples to reduction/oxidation cycles at temperatures between 800/1000 °C. The influence of the synthesis parameters on stability/reversibility was investigated. The material is completely stable up to 800 °C even in aggressive reducing atmospheres. Reduction occurring at higher temperatures is reversible: a simple treatment in oxygen is enough to entirely re-absorb the side phases formed during the reduction and obtain the starting material.     

Colossal dielectric permittivity in (Al+Nb) co-doped Ba0.4Sr0.6TiO3 ceramics

Stimulated by the outstanding colossal permittivity behavior achieved in trivalent and pentavalent cations co-doped rutile TiO₂ ceramics, the co-doping effects on the dielectric behavior of Ba_0.4Sr_0.6TiO₃ ceramics were further explored. In this work, (Al + Nb) co-doped Ba_0.4Sr_0.6TiO₃ ceramics were synthesized via a standard solid state ceramic route. The structural evolution was analyzed using X-ray diffraction patterns and Raman spectra. Dense microstructures with no apparent change of grain morphology were observed from the scanning electron microscopy. A huge enhancement of dielectric permittivity was obtained with 1 mol% (Al + Nb) doping and excellent dielectric performances (ε_r ∼ 20,000, tanδ ∼ 0.06 at 1 kHz) were achieved after further heat treatment. The formation of electron pinned defect dipoles localized in grains may account for the optimization of dielectric behaviors and the corresponding chemical valence states were confirmed from the XPS results.     

Enhanced Microwave Absorption Properties of Intrinsically Core/shell Structured La0.6Sr0.4MnO3 Nanoparticles

The intrinsically core/shell structured La_0.6Sr_0.4MnO₃nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption properties are investigated in the frequency range from 1 to 12 GHz. An optimal reflection loss of −41.1 dB is reached at 8.2 GHz with a matching thickness of 2.2 mm, the bandwidth with a reflection loss less than −10 dB is obtained in the 5.5–11.3 GHz range for absorber thicknesses of 1.5–2.5 mm. The excellent microwave absorption properties are a consequence of the better electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the particular core/shell microstructure. As a result, the La_0.6Sr_0.4MnO₃nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic wave absorption materials.     

Moisture Effect on La0.8Sr0.2MnO3 and La0.6Sr0.4Co0.2Fe0.8O3 Cathode Behaviors in Solid Oxide Fuel Cells

Moisture effect on cathode behaviors is a major issue for solid oxide fuel cells servicing under severe high temperature environments. This work studies the effect of dry air and moist air on La_0.8Sr_0.2MnO₃ (LSM821) and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF6428) cathodes at 800 °C by investigating the interfacial reaction and degradation through an AISI 441 interconnect/LSM821 (LSCF6428) electrode/yttria‐stabilized zirconia (YSZ) electrolyte tri‐layer structure. Under the same processing condition, the grain size of the LSCF6428 cathode is smaller than that of the LSM821 cathode. Ohmic resistance and polarization resistance of the cathodes are analyzed by deconvoluting the electrochemical impedance spectroscopy (EIS) results. The LSCF6428 cathode has much smaller resistance than the LSM821 cathode. Moisture produces a larger effect on the ohmic resistance and polarization resistance of the LSM821 cathode than on those of the LSCF6428 cathode. More chromium diffuses from the interconnect to the cathode for both LSM821 and LSCF6428 electrodes thermally treated in moist air. Based on the structure, elemental distribution, and EIS analysis, the interaction mechanisms between the electrodes and the AISI 441 alloy interconnect are proposed.     

Fast discharge and high energy density of nanocomposite capacitors using Ba0.6Sr0.4TiO3 nanofibers

Nanocomposites combining high breakdown strength (BDS) polymer and high dielectric permittivity ceramic fillers have shown great potential for pulsed power application. Here a new composite material based on surface-functionalized Ba_0.6Sr_0.4TiO₃ nanofibers/poly(vinylidene fluoride) (BST NF/PVDF) has been prepared by solution casting. The nanocomposites containing 2.5 vol% isopropyl dioleic(dioctylphosphate) titanate (NDZ 101)-functionalized BST NF (N-h-BST NF) have large energy density of 6.95 J cm⁻³ at 380 MV m⁻¹, which is 1.85 times larger than that of the pure PVDF at the same electric field. Also, the discharge speed of the nanocomposites containing 7.5 vol% N-h-BST NF is approximately 0.11 μs. The good properties, together with the large energy density and fast discharge speed, make this material a promising candidate for pulsed power capacitor.     

Fabrication of Barium Strontium Titanate (Ba0.6Sr0.4 TiO3) 3D Microcomponents from Aqueous Suspensions

This study reports on the fabrication of BST (Ba_0.6Sr_0.4TiO₃)‐based 3D microcomponents through an aqueous colloidal approach. The BST powder was synthesized by solid‐state reaction assisted by thermal analysis and XRD diffraction. Well crystalline cubic BST single phase was obtained upon heat‐treating the precursor powder mixture at 1200°C–1250°C. The reactivity of the BST powder toward water was evaluated by the changes in pH and concentration of leached ionic species along aging time. Hydrolysis reactions were suppressed by chemisorbing a suitable phosphate‐based protective agent and enabled an excellent dispersion ability to be achieved. Aqueous suspensions with solids loadings as high as 50 vol% that are stable against hydrolysis for several days could easily be prepared from the surface‐treated BST powder in aqueous solutions of an epoxy resin. After adding a suitable hardener, the colloidal suspensions could easily be cast into soft silicon rubber molds to obtain homogeneous and high dense green BST bodies.     

MgO对Ba0.6Sr0.4TiO3铁电陶瓷材料结构及低频特性的影响

研究了添加MgO的Ba0.6Sr0.4TiO3(BSTO)可调谐微波器件用铁电陶瓷材料的结构和低频下的介电性能.结果发现随着MgO添加量的增加,BSTO材料的相对介电常数大幅度下降,材料的密度和可调性也随之降低.SEM和XRD结果表明随MgO添加量的增加,材料晶粒尺寸减小,体系的晶胞参数略有下降,MgO在BSTO中以独立相的形式存在.制备出了相对介电常数较低(εr=181),介质损耗达4.7×10-3(在频率为10 kHz时),可调性为10.26%(电场为2.2 kV/mm)的适用于制作移相器的BSTO铁电陶瓷材料.     

Chemical Compatibility and Electrical Contact of LaNi0.6Co0.4O3–δ (LNC) between Crofer22APU Interconnect and La0.6Sr0.4FeO3 (LSF) Cathode for IT‐SOFC

In order to simulate the contact situation of interconnect/contact layer/cathode in SOFC stacks, contact resistance and chemical compatibility of LaNi_0.6Co_0.4O_3–δ (LNC) as contact layer between Crofer22APU interconnect and La_0.6Sr_0.4FeO₃ (LSF) cathode was investigated at 800 °C in air for more than 1300 h using X‐ray diffraction (XRD), scanning electron microscopy (SEM) set‐up equipped with an energy dispersive X‐ray analyser (EDX) and area specific resistance (ASR) measurements. The XRD analysis reveals that multiple phases were formed during ASR test. The point microanalysis on cross‐section of Fe–Cr/LNC/LSF system, after ASR measurements, shows chromium within the porous contact material mainly concentrated close to interconnect, but no Cr, Ni, or Co was detected in the cathode. It was found between LNC and LSF cathode, a thin and uniform layer which contains Sr, La, Cr, Co, Ni, and Fe. The contact between layers could act as a physical barrier for element migration and thus can suppress degradation of the cathode for these systems. The area specific resistance slope depends on the interactions between the contact material and/or cathode and the interconnect. Co‐containing spinels formed during ASR test can be responsible of the resistance decrease of the system, related to the low degradation of the cell.     

Impact of microwave sintering on dielectric properties of screen printed Ba0.6Sr0.4TiO3 thick films

The influence of 30 GHz microwave sintering compared to conventional sintering has been investigated on polycrystalline Ba_0.6Sr_0.4TiO₃ (BST60) thick films with respect to an application as tunable dielectrics. The BST thick films were prepared as metal–insulator–metal (MIM) capacitors on alumina substrates. The average grain size (440 nm) and the porosity (approx. 30%) of the sintered films are only little affected by the sintering method. However, permittivity, dielectric loss and tunability have been influenced substantially. The dielectric improvement by microwave sintering is interpreted in terms of an increased crystal quality (ξ_S) and/or a decrease of defect concentrations. It is assumed that microwave sintering preferably heats up parts of the film where an increased defect density exists and therefore causes a selective heating process. This may heal up charged defects, inhomogeneities, and structural defects.     

Effect of oxygen treatment on structure and electrical properties of Mn-doped Ca0.6Sr0.4TiO3 ceramics

Different oxygen treatment methods, including O₂ and N₂ annealing, were conducted on Ca_0.6Sr_0.4TiO₃ (CST) ceramics with varying Mn content (0?mol%, 0.5?mol% and 2.0?mol%). Structure characterization, including XRD and SEM, indicated the minimal effect of annealing on the microstructure. Grain boundaries were found to be sensitive to oxygen treatments, and annealing in O₂ resulted in increased grain boundary resistance, while in N₂ led to the opposite result. The insulating properties of bulk ceramics were found to be dominated by grain boundaries. Both the concentration and mobility of oxygen vacancies were confirmed to affect the energy storage properties to some extent in this work.     

The transient response study of CO,CO2, and O2 adsorption and CO oxidation over La0.4Sr0.6Co0.4Mn0.6O3

The transient behaviour caused by the change of the component concentration for CO oxidation on the perovskite‐type catalyst La_0.4Sr_0.6Co_0.4Mn_0.6O₃ was investigated. Results showed that CO was not adsorbed on the catalyst surface and CO oxidation was carried out between the surface oxygen species and gas phase CO. On the other hand, CO₂ can be adsorbed on the catalyst surface but its adsorption site was different from the forming site.     

PbO-SiO2玻璃对Ba0.4Sr0.6TiO3陶瓷致密度和介电性能的影响

为了制备耐高压、高储能密度陶瓷电容器,研究了不同PbO-SiO2(PS)玻璃添加量对Ba0.4Sr0.6TiO3陶瓷致密度和介电性能的影响。结果表明:PS玻璃能有效降低Ba0.4Sr0.6TiO3陶瓷的烧结温度,细化晶粒,提高样品的致密度。添加适量PS玻璃改善了Ba0.4Sr0.6TiO3陶瓷的介电性能。添加质量分数为1%PS玻璃的Ba0.4Sr0.6TiO3陶瓷在1100℃烧结致密,相对密度达到98.3%,平均击穿场强达到15.4kV/mm,相对于纯Ba0.4Sr0.6TiO3陶瓷的提高了1.5倍,1kHz的室温相对介电常数达到1179,介电损耗为6×10-4。