Electrical conductivity of YSZ-SDC composite solid electrolyte synthesized via glycine-nitrate method

Yttria-stabilized zirconia (YSZ) is a common solid electrolyte for solid oxide fuel cells (SOFCs) because of its high electrical conductivity and high ionic transference number in both oxidizing and reducing atmospheres. Samarium doped ceria (SDC) has also been considered as an alternative electrolyte material to YSZ for intermediate temperature SOFC because of its high conductivity at relatively low temperatures. Due to improved ionic conductivity of YSZ at high temperature (~ 800 °C) and good conductivity of SDC in the intermediate temperature range (600–800 °C), the electrical properties of YSZ-SDC composites were investigated. Composites of YSZ and SDC with weight ratio 9.5:0.5, 9:1 and 8.5:1.5 were synthesized via glycine-nitrate route. XRD pattern of the systems revealed the formation of composite phases. Biphasic electrolyte microstructures were observed, in which SDC grains are dispersed in YSZ matrix. Relative density of the compositions was found to be more than 92% to the theoretical density. It was observed that the interface provides a channel for ionic transport, leading to a notable ionic conductivity. With increase in SDC weight ratio the electrical conductivity was found to increase. For weight ratio 8.5:1.5 the electrical conductivity was found to be greater than that of YSZ in the temperature range 400–700 °C. Further, for weight ratio more than 8.5:1.5, conductivity was found to decreases due to the formation of a few other insulating impurity phases. The electrode polarisation was also found to reduce significantly with SDC in the composite electrolyte system. Thus, such composite system may be useful for improving the ionic conductivity of the composite electrolytes.     

Synthesis and enhanced visible light photocatalytic activity of WO3-BiOClxBr1−x heterojunctions with tunable energy band structure

A series of WO₃-BiOCl_xBr_1−x heterojunctions with tunable energy band structure were successfully synthesized via a hydrothermal method. The photocatalytic activities and reaction mechanism of WO₃-BiOCl_xBr_1−x composites were investigated by decomposition of Rhodamine B (RhB). The light absorption ability, energy band structure and photocatalytic activity in WO₃-BiOCl_xBr_1−x heterojunctions could be adjusted by changing the mole ratio of Br and Cl. The results revealed that the WO₃-BiOCl_xBr_1−x composites exhibited the highest photocatalytic activities than pure WO₃ and BiOCl_xBr_1−x under visible light irradiation. The photocatalytic property of WO₃-BiOCl can be strengthened mainly owing to the enhanced light absorption ability, while the photocatalytic activities of WO₃-BiOCl_xBr_1−x (x = 0, 0.25, 0.5 and 0.75) composites could be enhanced by restricting the recombination of photo-generated electrons and holes. Among them, 5% WO₃-BiOCl_0.25Br_0.75 heterojunction shows the highest photocatalytic activity with RhB completely decomposed in 6 min, this can be contributed to the synergetic effects of energy band structure and light absorption ability. Moreover, the holes and superoxide radical anions were considered as the active species during photocatalytic oxidation process, and the possible mechanism of the enhancement of the photocatalytic property was proposed.     

Luminescence properties and pigment properties of A-doped (Zn,Mg)MoO4 triclinic oxides (with A = Co,Ni, Cu or Mn)

First, we describe the phase diagram in between two oxides, ZnMoO₄ and MgMoO₄, with P-1 triclinic and C2/m monoclinic space groups, respectively. Based on the discovery of a large solid solution phase with a P-1 triclinic space group ranging from ZnMoO₄ to Mg_0.9Zn_0.1MoO₄, in this study, we investigate the potential influence of the magnesium/zinc ratio on the pigment/luminescent properties of compounds in the triclinic solid solution domain with formulae t-Mg_1−x−yZn_xA_yMoO₄, with 0.1 ≤ x ≤ 1 and with A²⁺ being a phosphor (Mn²⁺ (y = 0.01)) or chromophore cation (Co²⁺, Ni²⁺, or Cu²⁺ (y =0.1)). Various bright colours were obtained depending on the doping ion. Optical properties were fully interpreted by spectroscopic investigation and indexing of the absorption/excitation bands. Near white luminescence is obtained for both un-doped and Mn-doped t-Mg_1−xZn_xMoO₄ compounds, revealing a potential use as a white source. Bright yellow, blue or pale cyan colours can be achieved using nickel, cobalt or copper as chromophores, respectively, and the colours of the t-Mg_1−x−yZn_xA_yMoO₄ are moderately impacted by the Mg/Zn ratio.     

Catalytic activity improvement for efficient hydrogen oxidation of infiltrated La0.3Sr0.7Ti0.3Fe0.7O3-δ anode for solid oxide fuel cell

In this paper, a ceramic perovskite anode for solid oxide fuel cells (SOFCs) is prepared by infiltrating La and Fe co-doped strontium titanium, La_0.3Sr_0.7Ti_0.3Fe_0.7O_3-δ (LSTF0.7) into porous backbone of scandia-stabilized zirconia (ScSZ) and tested in pure H₂ at 700–850 °C. LSTF0.7 crystal exhibits high reduction stability and good compatibility with ScSZ electrolyte under reducing atmosphere. In order to improve the electrocatalytic activity, 15 wt% of CeO₂ and 7 wt% of Ni are infiltrated into the backbone pores respectively, thus forming LSTF0.7-CeO₂ and Ni-CeO₂-LSTF0.7 composite anodes. The cell with LSTF0.7 single anode shows a relatively lower maximal power density (MPD) of 401 mW cm⁻² in H₂ at 800 °C. While the maximal power densities of the cells with LSTF0.7-CeO₂ and Ni-CeO₂-LSTF0.7 composite anodes are 612 mW cm⁻² and 698 mW cm⁻² operated at the same conditions, respectively. The three anode polarization resistances (Rp,a) distinguished from the corresponding full cells are 0.176, 0.086 and 0.076 Ω cm² at 800 °C, respectively. The values of the activation energy (Ea) towards H₂ oxidation for the three anodes can be calculated to be 52.2, 46.0, 43.9 kJ mol⁻¹ based on their respective Rp,a. Therefore, the LSTF0.7-based anodes are considered to be promising alternatives for solid oxide fuel cell applications.     

Synthesis,structural and electrochemical properties of new ytterbium-doped langbeinite ceramics

In this work we have successfully synthesized highly pure phases of K₂Mg₂(SO₄)₃:xYb³⁺(x=0.2, 0.5 and 1 mol%) langbeinite powders denoted as KMgYbx (x=0.2, 0.5 and 1) using the solid-state reaction method. Structural characterization was carried out via the Rietveld method on the X-ray powder diffraction data and the results confirmed that the Yb³⁺ dopant can replace the magnesium in this structure with a slight increase of the lattice parameters. The electrical conductivity was studied by impedance spectroscopy in the [633–7237 K] temperature range and results show that the undoped sample was a low ionic solid electrolyte conductor. The doped materials show a semiconductor ionic character and the conductivity of K₂Mg₂(SO₄)₃:xYb³⁺ decreases when the Yb³⁺ dopant content x is increased. Results also show that K₂Mg₂(SO₄)₃:0.2Yb³⁺ has the highest electrical conductivity. It has therefore been concluded that doping with the appropriate amount of ytterbium trivalent and obtaining denser materials sintered at 1073 K can further improve the electrical properties of langbeinite.     

Lithium ion conductivity in the solid electrolytes (Li0.25La0.25)1−xM0.5xNbO3 (M=Sr,Ba, Ca,x=0.125) with perovskite-type structure

Perovskite-type structured solid electrolytes with the general formula (Li_0.25La_0.25)_1−xM_0.5xNbO₃ (M=Sr, Ba, Ca, x=0.125) have been prepared by solid-state reaction. Their crystal structure and ionic conductivity were examined by means of X-ray diffraction analysis (XRD), scanning electron microscope (SEM), and alternating current (AC) impedance technique. All sintered compounds are isostructural with the parent compound Li_0.5La_0.5Nb₂O₆. Some impurity phase is detected at the grain boundary in the Ba- and Ca-substituted compounds. The substitution of partial Li⁺ by alkaline earth metal ions has responsibility for the cell volume expansion as determined by the XRD data. The densification is accelerated, with the overall porosity and grain boundary minimized as Sr²⁺ ions are doped. Among the investigated compounds, the perovskite (Li_0.25La_0.25)_0.875Sr_0.0625NbO₃ shows a remarkable ionic conductivity of 1.02×10⁻⁵ S/cm at room temperature (20 °C) and the lowest activation energy of 0.34 eV in comparison with 0.38 eV and 0.44 eV for the corresponding Ba- and Ca-doped samples, respectively. It is identified that the enhancement of ionic conductivity is attributed to a reduction in activation energy for ionic conduction which is related to an increase in the cell volume.     

Samarium doped ceria (SDC) synthesized by a metal triethanolamine complex decomposition method: Characterization and an ionic conductivity study

Samarium doped ceria (SDC) powders as solid electrolyte ceramics were successfully prepared via thermal decomposition of metal organic complexes containing triethanolamine (TEA) as a ligand. The SDC powders synthesized using various samarium doping contents were characterized by X-ray diffractometry, scanning electron microscopy, X-ray absorption spectroscopy, energy dispersive X-ray spectroscopy and Brunauer-Emmett-Teller (BET) analysis. The influences of samarium doping and the calcination temperature on the characteristics of the SDC materials were thoroughly investigated. An appropriate temperature for SDC powder calcination was identified by thermogravimetric analysis to be 600 °C. After sintering the calcined SDC powders at 1500 °C to obtain highly dense ceramic pellets, the electrical conductivity of the materials was examined by impedance spectroscopy. The influence of percentage of Sm³⁺ dopants in SDC materials on the observed conductivity were explained by correlating with the detailed analysis of the local structure and environment of Sm³⁺ within the SDC materials by using X-ray absorption spectroscopy. The conductivities of the SDC products reported in this work indicate that they are promising candidates for solid electrolytes in solid oxide fuel cell applications.     

Phase-microstructure evolution and microwave dielectric characteristic of (1−x)(Sr0.5Ce0.5)TiO3+δ−xNdAlO3 solid solution

A perovskite solid solution (1−x)(Sr_0.5Ce_0.5)TiO_3+δ−xNdAlO₃, x = 0.1 to 0.4 was prepared by conventional solid state method. X-ray diffraction spectra revealed a single phase with tetragonal structure, indicating that doping of NdAlO₃ significantly stabilized the perovskite-like structure. The addition of NdAlO₃ facilitated the formation of large plate-like grains with porous microstructure. The dielectric constant (ε_r) decreased with increasing x because of the small ionic polarizability of NdAlO₃. The Q × f value was strongly dependent on the microstructure of these ceramics. The temperature coefficient of resonant frequency (τ_f) gradually shifted to near zero with a rise of x, which resulted from the decrease in tolerance factor (t). The solid solution with x = 0.4 sintered at 1550 °C for 4 h showed a good combination of dielectric properties: ε_r = 72, Q × f = 12052 GHz and τ_f = +5 pmm/°C.     

Preparation of Li2TiO3 by hydrothermal synthesis and its structure evolution under high energy Ar+ irradiation

Ultrafine lithium titanate (Li₂TiO₃) powder was synthesized by hydrothermal method. The phase formation and transition condition among α, β, and γ-Li₂TiO₃ were discussed. XRD and ICP-AES showed the single α-phase was formed at 180 °C with 2 h hydrothermal reaction, and it transited into β-phase at 400 °C. SEM observation and EDS analysis confirmed the dissolution of TiO₂ and the formation of α-Li₂TiO₃ proceeded simultaneously with preferable growth direction of (-133) lattice. During the phase transition, the powder maintained the small crystallite, which facilitated the fabrication of Li₂TiO₃ bulk with small grain size. After the Ar⁺ irradiation, the surface region to the depth of 3 μm of Li₂TiO₃ ceramic was affected, where the decrease of crystallization and disturbance of short-range order were confirmed by GIXRD and Raman spectroscopy. In spite of the structure change at the surface area, the ceramic bulk maintained the same.     

(Ti,V)_3AlC_2/Al_2O_3复合材料的制备及力学性能

为了提高Ti_3Al C_2陶瓷的力学性能,本研究以Ti C粉、Ti粉、Al粉和V2O5粉为起始反应原料,采用原位热压技术在1350°C下反应烧结合成出了(Ti,V)_3AlC_2/Al_2O_3复合材料。利用X-射线衍射和扫描电子显微技术对合成产物的物相和微观结构进行了表征,并分析了复合材料的合成机制。最后,对(Ti,V)_3AlC_2/Al_2O_3复合材料的力学性能进行了研究。测试结果表明:(Ti_(0.92),V_(0.08))_3Al C_2/10wt%Al_2O_3复合材料具有最佳的力学性能,其硬度、断裂韧性及抗弯强度分别为5.56 GPa、12.93 MPa·m~(1/2)和435 MPa,相比于单相Ti_3Al C_2材料分别提升了60%、108%和31%。