Structure and electrical conductivity of BaCe0.7In0.1A0.2O3−δ (A = Gd,Y) ceramics

BaCe_0.7In_0.1A_0.2O_3?δ (A = Gd, Y) ceramics were synthesized by solid state reaction method. The microstructure and electrical properties of BaCe_0.7In_0.1A_0.2O_3?δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 773–1073 K in different atmospheres. All BaCe_0.7In_0.1A_0.2O_3?δ ceramics exhibit a cubic perovskite structure. Relative densities of BaCe_0.7In_0.1A_0.2O_3?δ ceramics are above 92%. BaCe_0.7In_0.1Gd_0.2O_3?δ and BaCe_0.7In_0.1Y_0.2O_3?δ ceramics exhibit an excellent chemical stability against boiling water. The conductivity values of BaCe_0.7In_0.1Gd_0.2O_3?δ are higher than those of BaCe_0.7In_0.1Y_0.2O_3?δ in both air and dry hydrogen atmospheres. The highest conductivity is 4.6 × 10^?2 S cm^?1 for BaCe_0.7In_0.1Gd_0.2O_3?δ ceramic in air at 1073 K. BaCe_0.7In_0.1Gd_0.2O_3?δ ceramic with a conductivity value of 1.0 × 10^?2 S cm^?1 at 823 K in both air and dry hydrogen atmospheres is considered as a promising alternative for electrolytes of SOFC in view of decreasing the operating temperature and keeping both high conductivity and good chemical stability.     

Characterization of Ba0.5Sr0.5M1−xFexO3−δ (M = Co and Cu) perovskite oxide cathode materials for intermediate temperature solid oxide fuel cells

Ba_0.5Sr_0.5Co_1?xFe_xO_3?δ (x = 0.2, 0.6, and 0.8) and Ba_0.5Sr_0.5Cu_1?xFe_xO_3?δ (x = 0.6 and 0.8) perovskite oxides have been investigated as cathode materials for intermediate temperature solid oxide fuel cells. All the samples synthesized by a citrate–EDTA complexing method were single-phase cubic perovskite solid solutions. Then, the thermal expansion coefficient, electrical conductivities, the oxygen vacancy concentrations, the polarization resistances (R_p), and the power densities were measured. An increase in the Co content resulted in a decrease in the polarization resistance, the electrical conductivities at low temperatures, and the inflection point of the thermal expansion coefficient, but it led to an increase in the electrical conductivities at high temperatures, the oxygen vacancy concentrations, and the maximum power densities. The Cu-based system has similar behavior to the Co-based system; yet, in terms of the electrical conductivities, high Cu content gave a better result than low content for the entire range of temperatures.     

Mechanical properties and lifetime predictions of dense SrTi1-xFexO3-δ (x = 0.25, 0.35, 0.5)

New oxygen transport membrane materials based on SrTi_1-xFe_xO_3-δ, synthesized through solid state reaction and processed via tape casting were characterized with respect to their mechanical behaviour via depth-sensitive indentation and ring-on-ring flexural testing. The elastic moduli obtained by indentation with 1 N load for SrTi_1-xFe_xO_3-δ (x = 0.25, 0.35, 0.5) specimens were 147 ± 10 GPa, 123 ± 6 GPa and 158 ± 10 GPa, respectively. Fracture stress was accessed by ring-on-ring testing performed at 100 N/min and the obtained results were 92 ± 9 MPa, 117 ± 15 MPa, and 100 ± 15 MPa for SrTi_0.75Fe_0.25O₃, SrTi_0.65Fe_0.35O₃, and SrTi_0.5Fe_0.5O₃ respectively. Ring-on-ring tests conducted at different loading rates gave access to subcritical crack growth sensitivity and aided the prediction of the materials’ lifetime through stress-time-probability diagrams, where SrTi_1-xFe_xO_3-δ (x = 0.25, 0.35, 0.5) may resist for 1 year with a failure probability of 0.1% at least 15 MPa, 22 MPa, and 12 MPa respectively.     

A comparison study on the substitution of Y3+−Al3+ by M2+−Si4+(M = Ba,Sr, Ca,Mg) in Y3Al5O12: Ce3+ phosphor

Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ (M = Ba, Sr, Ca, Mg) phosphors were successfully prepared through a classic solid-state reaction method. The crystal structures, photoluminescence spectra, quantum yields, and thermal stabilities of the phosphors were investigated in detail. The results indicate that all Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ phosphors maintain the crystal structure of garnets. The emission peaks of Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ (M = Ba, Sr, Ca, Mg) phosphors are located at 537, 538, 554, and 565 nm, respectively. A red-shift trend of emission peak is observed with decreasing M radius, which can be ascribed to the increase in the crystal-field splitting in the Ce³⁺ 5d level owing to the co-doping of M²⁺−Si⁴⁺. Under 460 nm excitation, the luminescence quantum yields and thermal stabilities of the Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ phosphors decreased with the decrease of M radius. The IQE of the Y_1.94BaAl₄SiO₁₂:0.06Ce³⁺ phosphor is 92.89%, and the resistance to thermal quenching is improved to be 93.32% at 150°C. In addition, the color shifts of Y_1.94MAl₄SiO₁₂: 0.06Ce³⁺ phosphors with increasing temperature are all tiny, which also demonstrates good resistance to thermal quenching of luminescence. The linear shrinkage of Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ phosphors is significantly improved compared with that of YAG: Ce³⁺, which is expected to generate Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ transparent/translucent ceramics and fabricate high-powder w-LEDs for high-quality solid-state lighting in the future.     

Photoluminescence and structural characteristics of double tungstates A(M1−X PrX)W2O8 (A = Li,Cs, M = Al,Sc, La)

In this article, photoluminescence of Pr³⁺ ions in the double tungstate A(M_1?X Pr_X)W₂O₈ (A = Li, Cs, M = Al, Sc, La; 0.0 ≤ X ≤ 0.1) are characterised. By varying ion radius in A and M sites the crystal structure was modified and even in crystals with similar structural characteristics three distinctive types of luminescence are observed. When the substitution ions in both A and M sites are relatively small the host lattice exhibits luminescence dominantly. With the small A site ion (Li⁺) and the large M site ion (La³⁺, 1.03 Å) the Pr³⁺ ion exhibits prominent luminescence. With the very large A site ion (Cs⁺, 1.67 Å) and relatively small M site ion (Sc³⁺, 0.75 Å) the Pr³⁺ exhibits both the 4f²–4f5d excitation and the ³P_J manifold excitations in the absorption spectrum. These excitation levels lead to two strong emissions from the Pr³⁺. PL characteristics are discussed with respect to crystal structural criteria.     

Synthesis,structure, optical and magnetic properties of Nd1−xAxMn0.5Co0.5O3−δ (A = Ba,Sr and Ca; x = 0 and 0.25)

The structural, optical, and magnetic properties of polycrystalline Nd_1-xA_xMn_0.5Co_0.5O_3−δ (A = Ba, Sr and Ca; x = 0 and 0.25) perovskite oxides were investigated. The powder XRD pattern demonstrates that the unit cell volume decreases with the changing A-site dopant type. The estimated bandgap energy (Eg) from UV–vis spectroscopic for NdMn_0.5Co_0.5O_3−δ, Nd_0.75Ba_0.25Mn_0.5Co_0.5O_3−δ, Nd_0.75Sr_0.25Mn_0.5Co_0.5O_3−δ and Nd_0.75Ca_0.25Mn_0.5Co_0.5O_3−δ are 3.27, 3.82, 3.79 and 3.53 eV respectively. The substitution of divalent element alters the absorption spectrum, while the redshift optical transition was observed with an increasing ionic radius of dopant. Temperature-dependent magnetization exposes that the Curie temperature (TC) gradually decreases with the decreasing size of alkaline earth metals, and glassy nature was observed at a lower applied magnetic field. The observation of TC can be well explained by the considering of the cationic size disorder parameter in A-site than the random distribution of B-site ions.     

Influence of SiC dispersion and Ba(Sr) substitution on the thermoelectric properties of Ca3Co4O9+δ

Ca₃Co₄O_9+δ is a typical p-type thermoelectric oxide material with a low thermal conductivity. In this study, double-layered oxide samples Ca(Ba,Sr)₃Co₄O_9+δ dispersed with different SiC contents were obtained via the traditional solid phase reaction method. The effects of different elemental substitutions and SiC dispersion contents on the microstructure and thermoelectric properties of the samples were studied. The double optimisation of partial substitution of Ca-site atoms and SiC dispersion considerably improved the thermoelectric properties of Ca₃Co₄O_9+δ. Through the elemental substitution, the resistivity of the Ca₃Co₄O_9+δ material was reduced. Conversely, introducing an appropriate amount of SiC nanoparticles enhanced phonon scattering and was crucial in reducing its thermal conductivity. After double optimisations, the dimensionless thermoelectric figure of merit (ZT) values of both Ca_2.93Sr_0.07Co₄O_9+δ + 0.1 wt% SiC and Ca_2.9Ba_0.1Co₄O_9+δ + 0.1 wt% SiC achieved an optimum value of 0.25 at 923 K.     

Synthesis,Characterization, Reactivity of η 3-allylPd(L)(X), Where X = Cl and L = Imidazolylphosphine and Their Application in Aryl Amination Reactions

Synthesis of new mono-(imidazolylphosphine) palladium chloride complexes is reported. Imidazolyl phosphines reacted with allypalladium chloride dimer to form monophosphine palladium(II) complexes. Some of these complexes readily ionize to form stable square planar complexes in which the heterocyclic nitrogen coordinates to Pd, whereas in other cases, the acidity of the N–H proton was explored. Finally, activity of complexes as catalysts for aryl amination reactions was also investigated.

     

铁基钙钛矿化合物AFeO3(A=Ca,Sr,Ba)的光催化性能

通过柠檬酸-硝酸盐燃烧法合成了钙钛矿(ABO3)及类钙钛矿(A2B2O5)型化合物BaFeO3,Sr2Fe2O5,Ca2Fe2O5,BaCoO2 93,Sr2Co2O5.用X射线衍射,紫外-可见光分光光度计,红外光谱分析和扫描电镜检测了合成样品.样品经过450℃烧结2 h并在800℃烧结4 h而获得.实验表明:在B位元素相同的情况下,A位元素离子半径越大越容易形成钙钛矿结构.实验中合成的具有钙钛矿或类钙钛矿结构的氧化物具有不同程度的光催化性能.     

Physical–chemical property and activity evaluation of LaB0.5Co0.5O3 (B = Cr,Mn, Cu) and LaMnxCo1−xO3 (x = 0.1, 0.25, 0.5) nano perovskites in VOC combustion

The correlation between physical–chemical properties and activities of LaB_0.5Co_0.5O₃ (B = Cr, Mn, Cu) nano perovskites was studied in combustion of toluene. LaMn_0.5Co_0.5O₃ showed the highest activity among LaB_0.5Co_0.5O₃ catalysts and further optimization study was focused on LaMn_xCo_1?xO₃ (x = 0.1, 0.25, 0.5). The activity and reducibility of catalysts improved due to partial substitution of Co³⁺ by B cation. No direct relationship was between surface area and catalyst activity. T_50% of 2-propanol over LaMn_0.25Co_0.75O₃, LaMn_0.5Co_0.5O₃, LaMn_0.1Co_0.9O₃ and LaCoO₃ was 168, 200, 220 and 229 °C, respectively. LaMn_0.25Co_0.75O₃ was the optimum catalyst and showed robust stability in combustion of toluene and 2-propanol.     

Microwave absorption properties of (1 − x)La0.85Ag0.15MnO3/x graphene (x = 0, 3, and 5 wt.%) composites

Composite of (1 − x)La_0.85Ag_0.15MnO₃/x graphene (x = 0, 3, and 5 wt.%) and epoxy resin with a ratio of 4:1 were prepared to investigate the influence of the addition of graphene in (1 − x)La_0.85Ag_0.15MnO₃/x graphene on real and imaginary parts of permittivity, permeability, as well as microwave reflection loss (RL), using a vector network analyzer in the 8–18 GHz of the frequency range. It is found that the value of RL is smaller at x = 3 wt.% (−20.74 dB at 14.85 GHz) and 5 wt.% (−14.81 at 16.50 GHz) compared to at x = 0 wt.% (−8.89 dB at 15.90 GHz). The result indicates that microwave absorption properties significantly improved as a result of the addition of graphene. It is suggested that the addition of graphene enhanced the dielectric loss–related mechanism such as interfacial polarization and conduction loss resulting in an improvement of microwave absorption performance for both x = 3 wt.% and x = 5 wt.% samples. It also shows that the observed enhanced microwave absorption properties may also be influenced by the resistivity of the sample as x = 3 wt.% sample exhibits enhanced microwave absorption properties and the lowest resistivity among the studied samples.     

Etherification of n-butanol to di-n-butyl ether over H3PMo12 − xWxO40 (x = 0, 3, 6, 9, 12) Keggin and H6P2Mo18 − xWxO62 (x = 0, 3, 9, 15, 18) Wells–Dawson heteropolyacid catalysts

Etherification of n-butanol to di-n-butyl ether was carried out over H₃PMo_12 − xW_xO₄₀ (x = 0, 3, 6, 9, 12) Keggin and H₆P₂Mo_18 − xW_xO₆₂ (x = 0, 3, 9, 15, 18) Wells–Dawson heteropolyacid (HPA) catalysts. Acid strength of H₃PMo_12 − xW_xO₄₀ Keggin and H₆P₂Mo_18 − xW_xO₆₂ Wells–Dawson HPA catalysts was determined by NH₃-TPD (temperature-programmed desorption) measurements. The correlations between desorption peak temperature (acid strength) of the HPA catalysts and catalytic activity revealed that conversion of n-butanol and yield for di-n-butyl ether increased with increasing acid strength of the catalysts, regardless of the identity of HPA catalysts (without HPA structural sensitivity).     

CeO2掺杂(Ba,Sr,Ca) TiO3 基高压电容陶瓷的研究

采用固相烧结法合成0.97(Ba0.6Sr0.3Ca0.1)TiO3·0.03(Bi2O3·3TiO2)陶瓷材料,研究了掺杂稀土氧化物CeO2对陶瓷材料介电性能的影响.随CeO2加入量的增加,材料的介电常数先增大后减小再增大后减小,而介电损耗先减小后增大,击穿场强先增大后减小.当CeO2为0.1wt%时,介电常数最大,εr=2384.当CeO2为0.2 wt%时,获得了介电常数为1730,介电损耗为0.0060,耐压为13.125 kV/mm的高压低损耗陶瓷电容器瓷料.利用SEM分析了不同CeO2加入量时样品的断面形貌,结果表明:CeO2可以抑制晶粒生长,细化晶粒,形成固溶体,而过量的CeO2偏析于晶界.     

Improved dielectric strength and energy storage density in Ba6−3xLa8+2xTi18O54 (x = 0.5, 2/3, and 0.75) ceramics

Dielectric strength and energy storage density in Ba_6−3xLa_8+2xTi₁₈O₅₄ (x = 0.5, 2/3, and 0.75) ceramics were investigated as functions of composition and microstructure. With increasing x, although the dielectric constant decreased from 113 to 102, the energy storage density increased from 2.3 J/cm³ to 3.2 J/cm³ due to the increased dielectric strength for ceramics prepared by conventional sintering. The energy storage was further improved to 4.2 J/cm³ in ceramics prepared by spark plasma sintering under an electric field of 1058 kV/cm. Both dielectric strength and energy storage density in the present ceramics indicated the strong processing and microstructure dependence. The optimum dielectric strength and energy storage density were achieved in the dense ceramics with fine grains, while both dielectric strength and energy storage density decreased in the ceramics with coarse columnar grains.     

Thermochemical expansion of mixed-conducting (Ba,Sr)Co0.8Fe0.2O3−δ ceramics

The thermal and chemical expansion of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) and SrCo_0.8Fe_0.2O_3−δ (SCF) mixed ionic-electronic conductors were studied in combination with oxygen nonstoichiometry (δ) at 298–1223 K and p(O₂) = 10⁻⁴ to 1.00 atm. In order to minimize the effects of phase separation or oxygen-vacancy ordering processes, the data were collected in dynamic cooling mode using dense ceramic samples. The procedure was justified by a very fast equilibration at given p(O₂) in high-temperature range demonstrated for ceramics samples with different specific surface area. The difference in nonstoichiometry of BSCF and SCF at temperatures ≥973 K was found to be ≤0.03 oxygen atoms per formula unit. BSCF demonstrates favorably smaller chemical expansion compared to SCF and many other mixed conductors, originating from smaller δ variations and larger unit cell less sensitive to temperature and nonstoichiometry changes. Excessive thermochemical expansion impedes however the use of BSCF in single-phase fuel cell cathodes and planar mixed-conducting membranes.     

A study on proton conduction in a layered metal–organic framework,Rb2(adp)[Zn2(ox)3]·3H2O (adp = adipic acid,ox2 − = oxalate)

We newly synthesized a metal–organic framework (MOF) Rb₂(adp)[Zn₂(ox)₃]·3H₂O (adp = adipic acid; ox^2 − = oxalate), where the rubidium ions, carboxylic acid groups, and water molecules are located in an interlayer space of a two-dimensional (2-D) oxalate-bridged network. The structure of this compound was determined using single-crystal X-ray diffraction analysis. Hydrated phases of this compound were examined using thermogravimetry and water vapor adsorption measurements. Proton conductivity in this MOF was investigated by alternating current impedance measurements. Systematic comparison with previously reported isomorphous 2-D compounds A₂(adp)[Zn₂(ox)₃]·3H₂O (A = NH₄ and K) showed that the difference in the ionic radii of the cations leads to a difference in activation energy of proton conductivity and that absence of NH₄⁺ ions causes a significant decrease in proton conductivity, even though the ionic radius of Rb⁺ (1.52 Å) is closer to that of NH₄⁺ (1.61 Å) than that of K⁺ (1.38 Å).     

Fabrication of porous (Ba,Sr)(Co,Fe)O3-δ (BSCF) ceramics using gelatinization and retrogradation phenomena of starch as pore-forming agent

Porous (Ba,Sr)(Co,Fe)O_3-δ (BSCF) ceramics with high open porosity and good electrical conductivity was fabricated using Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), which shows a high mixed ionic-electronic conductivity. In general, during the fabrication of porous ceramics by the sacrificial template method using pore former particles, closed pores are easily formed unless sufficient pore former particles are added. In this study, we have devised a method using the gelatinization-retrogradation phenomena of starch for producing a porous body with an excellent percolated pore network structure. By dispersing BSCF and starch in an aqueous slurry (0–50% by weight) and heating, gelatinization of the starch occurred and the starch particles adhered to each other. Furthermore, in order to retain the percolated structure, the water solvent was removed by freeze-drying without heating to obtain a dried green body. The sintering behavior of the porous BSCF bodies prepared under various conditions was characterized by microstructural observations and relative density measurements. By optimizing the process conditions of the gelatinization and retrogradation, a porous body having an open porosity of 48.3%, and with 99% of the total pores open, was obtained. The matrix was also well connected and showed a sufficiently high conductivity which was similar to the porous bodies made by the traditional sacrificial template method.     

Ca and Pr substitution promoted the cell performance in LnSr3Fe3O10-δ cathode for solid oxide fuel cells

The substitution of Ca for Sr in the LnSr_3-xCa_xFe₃O_10-δ (x = 0–1.5, Ln = La, Pr, and Sm), Ruddlesden-Popper (RP) intergrowth structure was investigated to determine how the physical and electrochemical properties of this potential cathode material in solid oxide fuel cells (SOFCs) are impacted. A small amount of Ca incorporated into the structure reduced the thermal expansion coefficient, improved the electrical conductivity, and increased power density by up to 30% of a La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ electrolyte-supported single cell. The microstructure and oxygen permeability of the materials were independent of Ca substitution. A phase transformation of LaSr_3-xCa_xFe₃O_10-δ to perovskite was observed when the Ca composition of x > 1.0. Among the substitution of Pr and Sm for La in LaSr_2.7Ca_0.3Fe₃O_10-δ, only PrSr_2.7Ca_0.3Fe₃O_10-δ was pure with no phase transformation found. The co-substitution of Pr and Ca promoted the reduction of Fe, enhanced the oxygen permeation and active surface, and diminished the contact resistance at the cathode-electrolyte interlayer. The co-substitution of Ca and Pr delivered good electrochemical performance of approximately 354 mWcm⁻² at 800 °C on a 0.3 mm thick La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ electrolyte-supported cell and the lowest area specific resistance (ASR).     

Electrical characterization of room temperature humidity sensors in La0.8Sr0.2Fe1−xCuxO3 (x = 0, 0.05, 0.10)

Semiconducting oxide gas sensors based on La_0.8Sr_0.2Fe_1?xCu_xO₃ (x = 0, 0.05, 0.10) (LSF, LSFC05, and LSFC10, respectively) were prepared by screen-printing for humidity detection at room temperature.The thick-films were heat-treated at 800, 900 and 1000 °C for 1 h and all the compositions proved to be effective in humidity sensing and presented a good reproducibility between several measurements. However, the best results were obtained with LSFC10 fired at 800 °C which showed a detection limit of 15% relative humidity and a maximum sensor response of about 87%, higher than the previous results. Copper addition to lanthanum strontium ferrites proved to be effective in lowering the sensors’ detection limit.