La0.85Sr0.15Cr0.9Ni0.1O3-δCe0.8Sm0.2O1.9作为SOFC阳极材料的研究

较低的催化活性大大地限制了La0．85Sr0．15Cr0．9Ni0．1O3-δ-（LSCN）作为直接碳氢化合物燃料SOFC阳极材料的应用．本文尝试用Pechini法合成LSCN，并按重量比1：1向其中加入纳米Ce0.8Sm0.2O1.9（SDC）作为阳极材料．经1500℃高温烧结12h后，LSCN与SDC以及电解质YSZ仍可以保持各自独立的相结构．加入SDC没能提高阳极的电导率，但由于改善了阳极电解质界面的结合状况，扩展了电极反应的活性区域，使阳极材料的极化性能有了提高．显微结构观察品示．LSCN-SDC阳极存甲烷与氧中使用时没有碳沉积现象．     

Observation of Spin-Glass Behavior in La0.85Sr0.15CoO3 Single Crystals

The magnetic behavior of La_0.85Sr_0.15CoO₃ single crystals and polycrystals has been subjected to a controversial debate for the last several years; while some groups show evidence for phase separation, others show spin-glass (SG) behavior. Here, we present a comprehensive investigation of the structural, ac susceptibility, and dc magnetization properties of La_0.85Sr_0.15CoO₃ single crystals grown by float zone method. The structural analysis of XRD data by Rietveld refinement reveals the single crystallographic phase. The ac susceptibility results exhibit a frequency dependent peak shift (??2 K) and time-dependent memory effect below the freezing temperature. The characteristic time scale ?? _o calculated from this peak shift is found to be of ??10^?13 s which matches very well with typical values observed for a SG system. Further, the peak shift of the zero-field-cooling curves to lower temperature at higher dc fields is well described by the well-known de Almeida Thouless line, a characteristic of SG behavior. Thus, all our experimental findings confirm the existence of SG behavior in La_0.85Sr_0.15CoO₃ single crystals.     

Synthesis and magnetocaloric properties of La0.85K0.15MnO3 nanoparticles

In this paper, La_0.85K_0.15MnO₃ nanoparticles were successfully synthesized at relatively low calcinated temperature from a polyaminocarboxylate complex precursor with diethylenetriaminepentaacetic acid (H₅DTPA) as ligand, and the magnetocaloric properties were investigated. The phase transformation, chemical composition, and microstructure of La_0.85K_0.15MnO₃ nanoparticles were characterized by X-ray diffraction (XRD), thermogravimetric (TG), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and electron diffraction (ED). The results revealed that La_0.85K_0.15MnO₃ nanoparticles calcined at temperatures within the range of 600–1000 °C are of pure single-phase rhombohedral structure and the grain sizes were precisely controlled by varing the calcined temperature. The relationship between magnetocaloric properties and the calcined temperature of La_1?xK_xMnO₃ nanoparticles was also investigated systematically. From the magnetic measurements as function of temperature and magnetic applied field, we have discovered that the Curie temperature T_C is 274.5 K and is independent of the calcined temperature. From the measurements and calculation of isothermal magnetization at different temperatures, the maximum magneticentropy changes close to T_C (274 K) of the samples calcined at 600 °C, 800 °C and 1000 °C are 2.02, 3.06 and 3.56/kg K at H = 2T, respectively. Also La_0.85K_0.15MnO₃ nanoparticle displays a second-order phase transition. These results suggest that this material is a candidate for use as an active for magnetic refrigerent around the room temperature.     

Magnetodielectric properties of nano-crystalline BaZr0.15Ti0.85O3/La0.67Sr0.33MnO3 thin film heterostructures

The paper discuses synthesis of La_0.67Sr_0.33MnO₃ and BaZr_0.15Ti_0.85O₃ thin film heterostructures using modified Pechini method (citrate gel) and spin coating technique. The XRD spectra are determined for confirmation of the crystal structure and phase formation of thin film composites. The paper presents variation of real and imaginary parts of dielectric constant ε′, ε″ and tan δ as function of frequency between 100 Hz and 1 MHz and applied magnetic field up to 0.6 T. The paper, also discuses the effect of magnetic field on AC conductivity. The observed variation of magnetocapacitance and impedance spectra are analyzed in terms of a possible equivalent circuit model. The present analysis shows that the method of impedance spectra could be used to separate out the possible contributions to the magnetodielectric effect.     

Preparation of perovskite-type La0.85Sr0.15MnO3 particles by spray pyrolysis using a filter expansion aerosol generator

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Electrical and magnetic properties of Mg0.85Co0.15Fe2O4 ceramics with V2O5 additives

In this study, magnesium-cobalt ferrite (Mg_0.85Co_0.15Fe₂O₄) powder was synthesized using a solid-state synthesis method, followed by the liquid sintering using 0.50–3.00 wt% vanadium oxide (V₂O₅) at 1050 °C for 2 h. X-ray diffraction (XRD) studies confirmed the formation of spinel ferrite. Microstructure studies revealed that by increasing the amount of V₂O₅ from 0.50 to 3.00 wt%, the average grain size was reduced from 15.9?±?5.9 to 7.0?±?2.5 μm and the samples were highly densified. V₂O₅ promoted the sintering process and reduced the dielectric constant (ε′), loss tangent (tanδ), and increased electrical resistivity. A magnesium-cobalt ferrite sample with 25.4 dielectric constant, 0.078 loss tangent, and 9.0?×?10⁵ Ω.cm resistivity at 1 MHz was achieved using 3.00 wt% V₂O₅. Increasing V₂O₅ content caused increasing coercivity (Hc) from 89 to 129 Oe. Moreover, the maximum saturation magnetization (Ms) value of 26.8 emu/g was obtained for the sample containing 1.50 wt% V₂O₅. The small dielectric loss tangent of the samples at 1 MHz suggests applications of these ceramics in microwave devices.

     

Emulsion processing of SOFC materials Ca0.3La0.7CrO3, Sr0.16La0.84CrO3, and Sr0.2La0.8MnO3

A novel preparation route to the perovskite materials Ca_0.3La_0.7CrO₃, Sr_0.16La_0.84CrO₃, and Sr_0.2La_0.8MnO₃ is described. The method produces the phase pure perovskite phases after calcination at 700°C for 2 hours. The powders produced are unagglomerated, and consist of hollow spherical particles 0.15 m in diameter. EDX has shown that the careful control of reaction conditions is vital to control the phase composition, and that small changes in stoichiometry result in the production of unsinterable powder.     

Study of the Magneto-Resistivity and Dependence of Percolation in La0.75Ca0.1Sr0.15Mn1−x Ga x O3 Compounds

We present a study of the effect of Ga-doping on the physical properties of La_0.75Ca_0.1Sr_0.15Mn_1?x Ga _x O₃ (x=0.025, 0.075 and 0.1) compounds prepared by the sol-gel method. The variation of the magnetization (M) vs. temperature (T), under an applied magnetic field of 0.05 T, reveals a ferromagnetic–paramagnetic transition for all samples. The magnetization behavior and the Curie temperature T _C have shown a large dependence on the fractional composition x. In fact, the M(T) curves have revealed the presence of a long-range ferromagnetic state below T _C. The magnetotransport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements. We have noted that these samples present an electrical transition from a paramagnetic-semiconductor state to a ferromagnetic-metallic one, when decreasing temperature. We have used the phenomenological equation for conductivity under a percolation approach, which is based upon an approach that the system consists of the phase separated ferromagnetic metallic and paramagnetic insulating regions. We have then fitted the resistivity data measured in the range of 15–300 K and found that the activation barrier decreases with the raising Ga³⁺ ion concentration.     

Tailoring the multiferroic properties in Ba0.85Ca0.15Zr0.1Ti0.9O3/La0.7Sr0.3MnO3 bilayer heterostructures using residual strain

Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃/La_0.7Sr_0.3MnO₃ (BCZT/LSMO) bilayer multiferroic heterostructures with different BCZT layer thickness are fabricated by pulsed laser deposition technique. Structural characterization of XRD and TEM reveals the epitaxial growth of the bilayer heterostructures, whose residual strain reduces with increasing thickness. The room temperature multiferroic characteristics of the bilayer heterostructures are demonstrated by the simultaneously observed ferroelectric and ferromagnetic properties as well as the magnetoelectric effect. Due to the varying residual strain, the multiferroic properties of the bilayer heterostructures show strong dependence on the BCZT layer thickness, which significantly improves with increasing thickness. The largest magnetoelectric coefficient with α_E31 value of 355.2 mV/cm·Oe is achieved in BCZT/LSMO bilayer heterostructures with BCZT layer thickness of 150 nm.

     

SrCe0.85Y0.15O2.925的合成和导电性能

用高分子凝胶法制备了氧化物固体电解质SrCeo.85Yo.15O2.925,研究了单体与网络剂的配比、烧结温度等参数对相平衡关系和材料性能的影响.结果表明:当单体与网络剂的质量比是5:1,在1300℃烧结可以合成出单相钙钛矿结构的SrCeo.85Yo.15O2.925.样品的致密性随着烧结温度的升高而提高,在1300℃烧结出的样品密度大约为理论密度的95%;电导率随着样品密度的增大而增大,700℃时样品的电导率大于0.10 mS·m-1.     

Thickness-dependent dielectric and electrocaloric properties of Pb0.85La0.1(Zr0.85Ti0.15)O3 antiferroelectric thin films on stainless steel substrates

Journal of Materials Science: Materials in Electronics - Pb0.85La0.1(Zr0.85Ti0.15)O3 (PLZT) antiferroelectric (AFE) thin films with different thicknesses were prepared by the sol–gel method...     

Two-dimensional hole localization induced by Zn, Ni, and Mg dopings in Cu sites in La1.85Sr0.15Cu1-x M x O y

Samples of La_1.85Sr_0.15Cu_1-xM_xO_y(M = Ni, Zn, and Mg) with a wide range of dopant concentration (0≤x≤0.30) were synthesized. X-ray diffraction analysis shows that the Zn doping results in a tetragonal-orthorhombic transition asx- >0.15. while both Ni- and Mg-doped samples still remain tetragonal up tox = 0.3. Furthermore, the Ni, Zn, and Mg dopings all reduce the local Jahn -Teller distortion of the CuO₆ octahedron in a similar way. The metalinsulator transition at the region of higher doping levei (x> 0.1) is observed in all three doped systems. The observed metal-insulator transition can be well interpreted in the context of Anderson’s theory of disorder-induced localization. For most of the semiconducting-like samples with higher doping level (x> 0.1), the conductive behavior is dominated by two-dimensional variable-range-hopping (2D-VRH) with {ie-13-01} This suggests that all the dopings of Ni, Zn, and Mg in Cu sites cause the localization of the holes. In addition, a remarkable difference in the room-temperature resistivity for the heavily doped samples with the same dopant (Zn, Ni, Mg) concentrations is also observed. A possible explanation is provided for this phenomenon.     

Study of the Solid State Reactions between (La,Sr)(Ga,Mg)O3 and (La,Sr)MnO3, (La,Ca)CrO3, and Ni

The reactions between Sr and Mg substituted LaGaO₃, Sr substituted LaMnO₃, Ca substituted LaCrO₃, and Ni annealed at 650 and 1000°C for up to 1000 h have been studied. The experiments show that solid state reactions between the original phases occur forming additional compounds, for example LaSrGa₃O₇, LaSrGaO₄, La₄Ga₂O₉, and Ca₂Ga₂O₅. In addition, the chemical composition of LaGaO₃ changes during the heat treatments. At 650°C significant solubility of Cr and Ca in LaGaO₃ have been observed. The solid solubility of Mn and Ni in LaGaO₃ is moderate.     

Synthesis and polymerization of substituted ammonium sulfonate monomers for advanced materials applications

Sulfonated polymers have found use as ion-exchange membranes for use in fuel cells, water purification, electroactive devices, and inorganic materials templating and synthesis. Improving the materials for these applications and opening up new applications requires the ability to synthesis targeted or more complex sulfonated polymers, which includes tailoring the chemistry (copolymerization across a wider range of solubility) and/or polymer architecture (block, graft, nanoparticle). This article will summarize the recent work using sulfonated monomers with substituted ammonium counterions as a versatile route for enabling this goal. Two main benefits of these monomers are as follows. First, they are useful for preparing amphiphilic copolymers, which is a challenge using traditional acidic or alkali salt forms of sulfonated monomers. Second, sulfonated polymers with substituted ammonium counterions are useful polymers for obtaining unique material properties, such as organo-gelation of low polarity solvents or obtaining ionic liquid polymers for the fabrication of solid polymer electrolytes.