Structure and properties of (1-x)La0.67Sr0.33MnO3/xMnOδ multicomponent composite

(1-x)La_0.67Sr_0.33MnO₃/xMnO_δ [(1-x)LSMO/xMnO_δ] multicomponent composites were prepared. Their structure and properties were investigated as function of composition. X-ray diffraction and x-ray photoelectron spectroscopy confirmed the coexistence of MnO, Mn₂O₃ and MnO₂. It was found that MnO_δ introduction led to decreased average grain size and metal-insulator transition temperature. But it can increase maximum resistivity and magnetoresistance. The corresponding values were 2.0 μm, 370 K, 0.017 Ω cm, −24.7% (10 K, 2 T) for x = 0 and 0.7 μm, 225 K, 1.899 Ω cm and −25.6% (10 K, 2 T) for x = 0.3. However, the ferromagnetic Curie temperature was almost composition-independent with the value of 305 K. These results indicate that forming multicomponent composite by introducing ferromagnetic second phases can suppress the drawbacks of conventional ferromagnetic materials.     

Production of perovskite-like La1−xCaxMnO3+δ ferromagnetic thin films by electrochemical reduction

Ferromagnetic and perovskite-like thin films (<1m) of La1–xCaxMnO3+ have been routinely prepared by heat treatment of an amorphous La–Ca–Mn precursor. The precursor was electrodeposited cathodically in the absence of oxygen and water onto polished silver substrates from a nonaqueous solution of the components' nitrates. Analysis by X-ray diffraction and SQUID magnetometry shows these materials exhibit the appropriate structural and magnetic phases indicative of colossal magnetoresistance.     

Effect of microstructure on electrical and mechanical properties of La5.4WO12-δ proton conductor

The relationships between microstructural characteristics and electrical as well as mechanical properties of La_5.4WO_12-δ (LWO54) materials were studied. Polycrystalline LWO54 samples revealed identical transport mechanisms regardless of the sample microstructure. The studied samples show predominately proton conductor behaviour below 800?°C and become predominant n-type and oxygen ion conductors above this temperature. The magnitude of the total conductivity is enhanced with larger grain size and lower porosity. Young’s modulus decreased by 20% with increasing temperature up to 1000?°C regardless of grain size and atmosphere. Fracture strength was determined via ring-on-ring bending tests, yielding values that strongly depended on microstructural characteristics and homogeneity of the microstructure. Elevated temperature deformation studies revealed that creep is governed by cation diffusion mechanism.     

Variable optical properties of La0.5Sr0.5Co1-xNixO3-δ for high-temperature resistant code application

La_0.5Sr_0.5Co_1-xNi_xO_3-δ (x = 0, 0.1, 0.3, 0.5) ceramics were prepared via tape casting and solid state reaction process. The influence of Ni concentration on the optical properties of La_0.5Sr_0.5Co_1-xNi_xO_3-δ has been investigated. Results showed that the reflectance in the range of 0.3–15 μm decreased with the increment of Ni concentration, thereby causing a change in the color phase parameters and emissivity. Based on the difference in L* values and emissivity, the letters (HOT) and QR codes (NJTECH) were fabricated. The developed letters and QR codes could be identified both at room and high temperatures. Furthermore, the QR codes were read out successfully even underwent heat treatment at 1000 °C. The results in this work demonstrate a new application of La_0.5Sr_0.5Co_1-xNi_xO_3-δ ceramics.     

Magnetic and dielectric properties of BaFe1/2Sn1/2O3-δ ceramics

Ceramic samples of barium ferrostannate BaFe_1/2Sn_1/2O_3-δ have been prepared by the sol-gel and hydrothermal synthesis methods. To reduce the number of oxygen vacancies, annealing in oxygen has been performed. The heat capacity, magnetization, Mössbauer and dielectric spectroscopy data point to the appearance of antiferromagnetic ordering below ～55 K followed by further spin glass magnetic ordering below 15 K. The giant dielectric response seems to be due to the relaxation of electrons trapped by oxygen vacancies. Comparison of the Fe K-edge X-ray absorption spectra of BaFe_1/2Sn_1/2O_3-δ confirmed substantial difference from those of the similar stoichiometric BaFe_1/2Nb_1/2O₃ perovskite.     

Structure and microwave dielectric properties of La(Mg0.5Ti0.5)O3–CaTiO3 system

(1−x)La(Mg_0.5Ti_0.5)O₃ (LMT)–xCaTiO₃ (CT) [0<x<1] ceramics were prepared from powder obtained by a nonconventional chemical route based on the Pechini method. The crystal structure of the microwave dielectric ceramics has been refined by Rietveld method using X-ray powder diffraction data. LMT and CT were found to form a solid solution over the whole compositional range. The 0.9LMT–0.1CT composition was refined using P2₁/n space group, which allows taking into account B-site ordering. The compounds having x⩾0.3 were found to be disordered and were refined using Pbnm space group. Microstructure evolution was also analysed. Dielectric characterization at microwave frequencies was performed on the LMT–CT ceramics. The permittivity and the temperature coefficient of resonant frequency of the solid solutions showed a non-linear variation with composition. The quality factor demonstrates a considerable decrease with the increase of CT content.     

Control of oxygen deficiency in Ca1−x La x MnO3−δ and its cathodic properties in alkaline solution

Ceramic samples of composition Ca_0.9La_0.1MnO_3– having various oxygen contents were prepared by a quenching method under nitrogen atmosphere. As the 3 – value decreased from 2.97 to 2.79, the sample conductivity decreased from 10² to 10^–1 S cm^–1. The porous ceramic samples showed good properties as cathode materials in alkaline solution without using conductive material such as graphite, but the discharge capacity decreased with decreasing sample conductivity. The discharge termination is explained by a simple model considering dissipation of the conductive path (high conductivity core) present in the porous sintered ceramic.     

Structural and superconducting properties of Y(Ba1-xKx)2Cu3O7-δ ceramics

Y(Ba_1-xK_x)₂Cu₃O_7-δ ceramics (x = 0.00, 0.03, 0.05 and 0.08) were synthesized by thermal treatments of aqueous solution of metals nitrates and polyvinyl pyrrolidone (PVP) that acts as a capping agent. The effects of K-substitution on the crystal structure, microstructure and electrical resistance of samples were investigated. The X-ray diffractions results indicated an improvement of crystallinity and variation of lattice constant, a, b and c of YBa₂Cu₃O_7-δ (Y123) phase with K-substitution. The K-substitution resulted in increasing of orthorhombicity factor compared to pure Y123. Microstructural observation using scanning electron microscopy showed that K-substitution promotes the grain growth of Y123. The superconducting transitions (T_c) of the substituted-samples were higher than that of the pure Y123. The T_c (onset) were 93, 97, 95, 95 K for the samples with x = 0.00, 0.03, 0.05 and 0.08, respectively. Comparing with pure sample, the substituted-samples showed sharper superconducting transition (ΔT_c). The best superconducting properties was observed for sample with x = 0.03.     

Experimental and theoretical study on enhanced electrical properties of nickel-substituted La0.5Sr0.5CoO3−δ ceramics

The effect of Ni substitution on the thermal behavior, crystal structure, densification, and electrical properties of La_0.5Sr_0.5Co_1–yNi_yO_3-δ (y = 0.00–0.08) (LSCN) ceramics was discussed based on experimental measurements and theoretical calculations to search for a ruthenium–free and lead–free conductive oxide for thick film resistors. Ceramics were synthesized by the solid–state reaction, and calculations were performed with first–principle density functional theory (DFT). Results showed that the replacement of Ni ion to Co ion could help decrease the densification temperature and enhance the densification level and improve the conductivity of LSCN. Theoretical calculations, including the crystal structure, bond population, total energy, and density of states (DOS), supported the experimental results well. The maximum conductivity of 3155 S/cm was achieved as y = 0.04 was sintered at 1200 °C, and the peak temperature coefficient of resistance (TCR) of 2405.7 ppm/°C occurred at y = 0.06.     

微波固相反应合成La1-xSrxCoO3阴极材料的研究

以碳酸盐或氧化物为原料, 采用微波固相反应合成技术成功地合成了纯钙钛矿结构的La1-xSrxCoO3(LSC, x=0.10～0.50)粉体.研究表明La2O3和SrCO3是2.45 GHz微波透明材料, 而Co3O4则具有很强的微波偶合吸收能力;La2O3, SrCO3, Co3O4混合料中SrCO3含量对混合物的微波吸收行为以及LSC的合成条件有很大影响.与传统的固相反应合成法相比, 微波固相反应合成法的反应合成时间大大缩短, 在输出功率700～800 W条件下, 反应时间≤25 min, 这归因于反应物与微波的直接偶合和反应物对微波能量的高效率吸收.     

Structural,optical, and electrical properties of conducting p-type transparent Cu–Cr–O thin films

Cu–Cr–O films were prepared by DC magnetron co-sputtering using Cu and Cr targets on quartz substrates. The films were then annealed at temperatures ranging from 400 °C to 900 °C for 2 h under a controlled Ar atmosphere. The as-deposited and 400 °C-annealed films were amorphous, semi-transparent, and insulated. After annealing at 500 °C, the Cu–Cr–O films contained a mixture of monoclinic CuO and spinel CuCr₂O₄ phases. Annealing at 600 °C led to the formation of delafossite CuCrO₂ phases. When the annealing was further increased to temperatures above 700 °C, the films exhibited a pure delafossite CuCrO₂ phase. The crystallinity and grain size also increased with the annealing temperature. The formation of the delafossite CuCrO₂ phase during post-annealing processing was in good agreement with thermodynamics. The optimum conductivity and transparency were achieved for the film annealed at approximately 700 °C with a figure of merit of 1.51×10⁻⁸ Ω⁻¹ (i.e., electrical resistivity of up to 5.13 Ω-cm and visible light transmittance of up to 58.3%). The lower formation temperature and superior properties of CuCrO₂ found in this study indicated the higher potential of this material for practical applications compared to CuAlO₂.     

Fabrication and H2 flux measurement of asymmetric La27W3.5Mo1.5O55.5-δ − La0.87Sr0.13CrO3-δ membranes

Novel asymmetric hydrogen permeable membranes consist of a dense ceramic–ceramic (cercer) composite layer of La_0.87Sr_0.13CrO_3-δ and La₂₇W_3.5Mo_1.5O_55.5-δ deposited on a tubular porous support of the latter composition. The membranes were produced by extrusion and dip-coating with various thermal cycles required for adjusting the thermal shrinkage of the different layers and obtaining gas tight membrane layers. The produced asymmetric membranes have a dense cercer layer thicknesses ranging from 25 to 50 μm on supports exhibiting a porosity of up to 40 vol%. The effect of processing parameters, such as volume of pore former, coating steps, sintering temperature and soaking time on the microstructure of the membranes is discussed to highlight critical steps in the manufacturing protocol. Hydrogen fluxes were measured as a function of temperature with both wet and dry Ar sweep gas. Results are discussed with respect to membrane architectures and materials properties.     

Thermoelectric properties of non-stoichiometric CaMnO3-δ composites formed by redox-activated exsolution

A novel synthesis route for preparing well-defined composites based on CMO (CaMnO₃) has been established taking advantage of the unique phase relations in the system Ca-Mn-O at reducing- and oxidizing atmosphere, respectively. Samples corresponding to stoichiometric CMO and composites with 5 and 10 vol % of Ruddlesden-Popper (Ca₄Mn₃O₁₀)- and spinel (CaMn₂O₄)-phases, respectively, were prepared with final densities >91 %. The presence of secondary phases significantly enhanced the electrical conductivity compared to stoichiometric CMO. The highest electrical conductivity was observed for CMO with 10 vol % spinel varying between 55 and 75 S/cm at temperatures between 100 and 900 °C. This composition also exhibited the highest figure-of-merit (zT) in this study, reaching 0.083 at 800 °C.     

Preparation and characterization of La0.7Sr0.3Cr1-xFexO3-δ anode catalyst with sulfur tolerance for SOFC

采用尿素燃烧法制备了La0.7Sr0.3Cr1-xFexO3-δ（x=0.2,0.3,0.4,0.5）系列阳极材料。采用TG-DTA、XRD对所制备的材料进行表征,利用直流四探针法测定催化剂在400～850 ℃温度时在空气中的电导率,并测试了电池电化学性能。结果表明：LSCrF系列材料具有很好的热稳定性,钙钛矿相晶型结构完整,与BaCe0.475Zr0.425Y0.1O3-δ电解质之间具有较好的化学相容性。同时,XRD显示LSCrF系列材料在硫化氢气氛中具有很好的化学稳定性。LSCrF7355在850℃的电导率最大为1.18 S/cm,其单电池的开路电压值为0.76 V,最大输出功率为7.16 mW/cm2,满足固体氧化物燃料电池阳极催化剂的要求,是一种新型的耐硫阳极材料。     

High-conducting Bi4V2−xFexO11-δ ceramics containing Fe2O3 nanocrystals: Structure and properties

The topography, structure, thermal, magnetic, and electrical properties of Bi₄V_2?xFe_xO_11-δ ceramics substituted with x = 0.5 and 0.7 Fe were studied. The microscope analysis showed the presence of iron-rich nanocrystals formed on the Bi-Fe-V-O grains. The X-ray diffraction studies confirmed that grains are built mostly of tetragonal Bi₄V_1.5Fe_0.5O_10.5 phase. Thermal properties analysis showed an order-disorder type γ ? γ? phase transition at a temperature of around 916 K, pronounced in samples doped with x = 0.5 Fe. The magnetic anomaly was observed in ceramics doped with x = 0.7 Fe which was assigned to Morin transition of Fe₂O₃. The conductivity was measured over a wide frequency range from 10 mHz to 1 MHz and at a wide temperature range from 373 to 923 K, using impedance spectroscopy. The D.C. conduction process was due to oxygen vacancies hopping while at low temperatures electron holes hopping is also possible.     

Structural and mechanical properties of La0.6Sr0.4M0.1Fe0.9O3-δ (M: Co,Ni and Cu) perovskites

La_0.6Sr_0.4M_0.1Fe_0.9O_3-δ (M: Co, Ni and Cu) perovskite nanostructures were synthesized using low frequency ultrasound assisted synthesis technique and effect of substitution of Fe by Co, Ni and Cu on crystal structure and mechanical properties in La_0.6Sr_0.4FeO_3-δ perovskite was studied. The HRTEM and Rietveld refinement analyses revealed the uniform equi-axial shape of the obtained nanostructures with the existence of La_0.6Sr_0.4M_0.1Fe_0.9O_3−δ with mixed rhombohedral and orthorhombic structures. Substitution by Cu decreases the melting point of La_0.6Sr_0.4FeO_3-δ. The results of mechanical characterizations show that La_0.6Sr_0.4Co_0.1Fe_0.9O_3−δ and La_0.6Sr_0.4Ni_0.1Fe_0.9O_3−δ have ferroelastic behavior and comparable elastic moduli, however, substitution by Ni shows higher hardness and lower fracture toughness than Co in B-site doping.     

Densification,morphological and transport properties of functional La1–xBaxYbO3–δ ceramic materials

The effective operation of protonic ceramic electrochemical cells requires the design of electrolytes having not only high ionic conductivity, but also excellent stability with respect to carbonisation. In the present work, the La-based oxides (La_1–xBa_xYbO_3–δ, 0.03 ≤ x ≤ 0.10) are proposed as a possible alternative to the convenient Ba(Ce,Zr)O₃-based electrolytes due to their high chemical stability. It was discovered that Ba-doping results in a deterioration of sintering behaviour; as a result, the relative density decreases and open porosity appears (for x = 0.10). A thorough analysis of transport properties by means of AC and DC measurement techniques enables a selection of the La_0.97Ba_0.03YbO_3–δ sample, which demonstrates the highest conductivity compared with those samples where x = 0.5 and 0.10. Due to its excellent densification behaviour, stability and ionic conductivity, La_0.97Ba_0.03YbO_3–δ can be considered as a promising proton-conducting electrolyte in the La-based family.