Preparation of In2O3-Sr2RuErO6 Composite Ceramics by the Spark Plasma Sintering and Their Thermoelectric Performance

In1.94Zn0.03Ge0.03O3 and Sr2RuErO6 composite ceramics have been prepared by the spark plasma sintering (SPS) technique. Microstructure studies show that the Sr2RuErO6 phases are randomly dispersed in the In1.94Zn0.03Ge0.03O3 matrix. The results show that the Seebeck coeffcient increases with increasing the amount of Sr2RuErO6, while the thermal conductivity of the composite samples is lower than that of the In1.94Zn0.03Ge0.03O3 ceramic. The thermal conductivity of the 7 vol.% Sr2RuErO6 sample can decrease to 2.15 W·m-1·K-1 at 973 K, and the evaluated maximum ZT value is 0.23 for 3 vol.% Sr2RuErO6 samples at 973 K, which makes them promising materials for the thermoelectric devices.     

Effect of Sintering Temperature on the Texturing Behavior of NaCo_2O_(4-δ) Synthesized by Urea Auto-Combustion Method

Polycrystalline NaCo2O4-δ materials were prepared using the urea auto-combustion method. The reaction process and crystal growth were investigated through X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), and Fourier transform infrared spectrometry (FTIR). The results indicate that the formation temperature of NaCo2O4-δ is about 620°C, which is lower than that for solid-state reaction. XRD results show that the texturing along c-axis occurred as the powders calcined at 700°C ...     

Preparation and Characterization of Ca3Co4O9 Thin Films on Polycrystalline Al2O3 Substrates by Chemical Solution Deposition

Ca3Co4O9 thin films have been first prepared on polycrystalline Al2O3 substrates using chemical solution deposition method by multiple annealing processing. It is observed that the derived thin films are c-axis oriented although the substrates are polycrystalline Al2O3 substrates, suggesting the self-assembled c-axis orientation. The annealing temperature effects on the properties are investigated and discussed. The best performances are attributed to the 850℃-annealed sample, whose resistivity, Seebeck coefficient and power factor at 300 K are 7.4 mΩ cm, 117 μV/K and 0.18 mW/m K-2 respectively, which is even better than those of the thin films deposited on single crystal substrates. The results will provide an effective route to optimize the properties of Ca3Co4O9 thin films using chemical solution deposition by multiple annealing processing even the substrates are polycrystalline.     

High-temperature Electric Properties of Polycrystalline La-doped CaMnO3 Ceramics

Polycrystalline La-doped CaMnO3 ceramics have been prepared by a solid-state sintering method.Analysis of microstructure and phase composition indicates that the addition of La can prohibit the further growth of grain,and no impurity phase appears.The results revealed that the La doping can lead to a large change of the activation energy(from 0.22 to 0.02 eV),and thus result in a marked increase in electric conductivity of 2-4 orders of magnitude.The power factor can reach about 1.5×10-4 W·m-1·K-2 in a wide...     

Transport Properties of K_xV_2O_5·nH_2O Nanocrystalline Films

Five different compositions of K x V 2 O 5 ·nH 2 O(where x=0.00,0.0017,0.0049,0.0064 and 0.0091 mol) were prepared by the sol-gel process.Electrical conductivity and thermoelectric power were measured parallel to the substrate surface in the temperature range of 300-480 K.The electrical conductivity showed that all samples were semiconductors and that conductivity increased with increasing K content.The conductivity of the present system was primarily determined by hopping carrier mobility.The carrier density was evaluated as well.The conduction was confirmed to obey non-adiabatic small polaron hopping.The thermoelectric power or Seebeck effect,increased with increasing K ions content.The results obtained indicated that an n-type semiconducting behavior within the temperature range was investigated.     

NaCo2O4及其Na位掺杂热电材料的制备研究

NaCo2O4是氧化物热电材料的典型代表,也是目前人们研究较多的一种热电材料,本文采用固相反应法和溶胶-凝胶法对NaCo2O4以及Na位掺杂K、Ca、Sr、Ce试样进行制备研究.选择合适的工艺参数,采用快速升温法,可获得纯度较高(大于94%)的NaCo2O4,并使掺杂元素K、Ca、Sr进入到NaCo2O4晶格中,而Ce由于原子半径太大,难以掺杂入NaCo2O4晶格.实验结果表明采用柠檬酸溶胶-凝胶法比固相反应法制备的试样晶粒尺寸更细小,增加声子散射,使晶格热导率降低,由此提高材料的热电优值,进一步改善材料的热电性能.     

Thermal analysis of glasses in TeO2-BaF2-LaF3 systems

Divalent metal fluorides MF2 （M=Sr, Mg, Ca） in oxyfluoride tellurite glasses TeO2-BaF2-LaF3 were synthesized. The densities, refractive indices and characteristic temperatures of synthesized glasses were measured. The influence of divalent metal fluorides-MF2（M=Sr, Mg, Ca） on the thermal stability of oxyfluoride tellurite glasses TeO2-BaF2-LaF3 were studied. Results show that the replacement of BaF2 by SrF2 and MgF2 can enhance the thermal stability against crystallization of the glass. A glass system with good thermal stability was produced, which could be a potential candidate for the host materials of the fiber devices.     

Thermomechanical Analysis of (Cu0.5Tl0.5)-1223 Substituted by Pr and La

The thermomechanical analysis (TMA) of Cu 0.5 Tl 0.5 Ba 2 Ca 2 x R x Cu 3 O 10 δ,where R=Pr and La,with 0.0≤x≤0.15,was carried out in temperature range from 450 to 1145 K.The samples were prepared by singlestep solid state reaction technique.The prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The superconductivity of the prepared samples was investigated by electrical resistivity measurement.The results showed that low substitution content enhanced the (Cu 0.5 Tl 0.5)1223 phase formation,while the higher substitution content degraded this phase.The higher superconducting transition temperatures T c were found to be 114 K and 109 K at x= 0.025 for Pr-and La-substitutions,respectively.The average linear thermal expansion coefficient increased as x increased,while the shrinkage temperature decreased as x increased.Those results were emphasized by porosity and Vickers microhardness calculations.Debye temperature θ D was calculated from the linear thermal expansion coefficient data and correlated to T c to estimate the electron-phonon coupling λ ep.     

Effect of Nb on the Interfacial Wettability in Al_2O_3/Medium Mn Steel

To develop medium Mn steel (MMS) matrix composites reinforced by AI2O3 particles, the effect of Nb on the interfacial wettability of AI2O3/MMS and its mechanism were investigated in this paper. The results show that the wetting angle of the specimens with different Nb contents are bigger than that of the specimen without Nb at the first stage, and then decreases with time at 1450℃. At certain time, the wetting angle is lower than that of the specimen without Nb. At 1550 and 1600℃, the wetting angle of the specimens containing Nb decreases quickly with time at first stage. After 10 min, the wetting angle reaches a steady state, and hardly changes with time. The mechanisms of Nb to improve the wettability can be attributed to the enrichment of Nb at the interface and Nb serves as surface active agent of MMS at T<1550℃, and as catalyzer for the interfacial reaction of AI2O3/MMS at T>1550℃, and reduces the interfacial energies.     

Structural,Sintering and Electrical Properties of Cr-doped La0.6Sr0.4CrxFe1-xO3-δ（x=0.10,0.20） Oxides

The perovskite Cr-doped La0.6Sr0.4CrxFe1-xO3-δ(x=0.10,0.20) oxides were synthesized via the citrate gel method.The perovskite forming of the La0.6Sr0.4CrxFe1-xO3-δ(x=0.10,0.20) oxides were studied by thermogravimetric analysis(TG),differential scanning calorimetry(DSC),and X-ray diffraction(XRD).Structural and chemical stability under H 2-containing helium atmospheres of La0.6Sr0.4CrxFe1-xO3-δ(x=0.10,0.20) were investigated by TG and XRD.The sintering microstructures of the perovskite La0.6Sr0.4CrxFe1-xO3-δ(x=0.10,0.20) ceramics were investigated by scanning electron microscopy(SEM),and the electrical conductivities of both oxide ceramics were also measured up to 900 C.The results demonstrated that the chemical stability of the Co-free La0.6Sr0.4CrxFe1-xO3-δ(x=0.10,0.20) oxides was significantly improved compared to the Co-containing La0.6Sr0.4Co0.2Fe0.8O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ oxides.The incorporation of Cr cations in the B-site of the pervoskite oxides resulted in the improved structural and chemical stability of the as-synthesized La0.6Sr0.4CrxFe1-xO3-δ(x=0.10,0.20) oxides.     

Magnetic and magnetocaloric properties of nanocrystalline Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) manganites

Structural, magnetic and magnetocaloric properties of sol-gel prepared, nanocrystalline oxides Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) (cubic, space group Fm3m) have been studied. From the X-ray data, the crystallite size of Pro.7Ca0.3Mn0.5Co0,503 and Pr0.7Sr0.3Mn0.5Co0.5O3 samples is found to be approximately 24 nm and approximately15 nm respectively. High resolution transmission electron microscopy image shows average particle size of approximately 34 nm and approximately 20 nm. Magnetization measurements indicate a Curie temperature of approximately 153 K and approximately172 K in applied magnetic field of 100 Oe for Pr0.7Ca0.3Mn0.5Co0.5O3 and Pr0.7Sr0.3Mn0.5Co0.O3 compounds. The magnetization versus applied magnetic field curves obtained at temperatures below 150 K show significant hysteresis and magnetization is not saturated even in a field of 7 T. The magnetocaloric effect is calculated from M versus H data obtained at various temperatures. Magnetic entropy change shows a maximum near T(c) for both the samples and is of the order approximately 2.5 J/kg/K.     

Thermoelectric properties of nanocrystalline Ca(3-x)Cu(x)Co4O9 (0 < or = x < or = 0.32) for power generation

We successfully synthesized nano-sized Ca(3-x)Cu(x)Co4O9 (0 < or = x < or = 0.32) powders by solution combustion process. Plate-like grains and porous structure were observed in the sintered Ca(3-x)Cu(x)Co4O9 ceramics. The sintered Ca(3-x)Cu(x)Co4O9 showed a monoclinic symmetry. The electrical conductivity of the Ca(3-x)Cu(x)Co4O9 increased with increasing temperature, indicative of a semiconducting behavior. The added Cu led to a significant increase in the electrical conductivity. The Seebeck coefficient of the Cu-added Ca(3-x)Cu(x)Co4O9 was much higher than that of the Cu-free Ca3Co4O9. The highest power factor (9.99 x 10(-4) Wm(-1)K-2) was obtained for Ca2.76Cu0.24Co4O9 at 800 degrees C.     

钴酸盐热电材料研究进展

热电材料具有重要而广阔的应用前景。氧化物热电材料可以避免传统热电材料的一些缺点而倍受重视。本文综述了NaCo2O4、Ca3Co4O9和Ca3Co2o6等系列的晶体结构、制备方法、元素掺杂与改性、电子结构计算与理论分析等．并探讨了钴酸盐热电材料的进一步发展方向。     

Ionizable (Thia)calix[4]crowns as highly selective 226Ra2+ ionophores

The 226Ra2+ selectivity of the ionizable (thia)calix[4]crowns 1-4 was determined in the presence of a large excess of the most common alkali and alkaline earth cations. Selective 226Ra2+ (2.9 x 10(-)(8) M) extraction occurs even at extremely high M(n+)/226Ra2+ ratios of 3.5 x 10(7) [M(n+) = Na+, K+, Rb+, Cs+, Mg2+, Ca2+, and Sr2+ (1M)] and an ionophore concentration of 10(-4) M. The selectivity coefficients log(K(Ra)(ex)/K(M)(ex)) are approximately 3.5 for Mg2+, Ca2+, and Sr2+. In the presence of Ba2+, which has very similar chemical properties, only the thiacalix[4]crown-6 derivative 4 showed a selectivity for 226Ra2+. In addition to the remarkable 226Ra2+ selectivities, the effective pH range (pH 8-13) of the thiacalix[4]crown dicarboxylic acids (3 and 4) allows for full regeneration of the ionophores at lower pH values (pH <6).     

High-temperature thermoelectric properties of Na(Co0.91, Ni0.09)2O4 fabricated by solution combustion method for power generation

High-quality nano-sized Na(Co0.91Ni0.09)2O4 powders, i.e., 27 nm in average size, were synthesized by the solution combustion route. The magnitude of the electrical conductivity, the Seebeck coefficient, and the power factor for Na(Co0.91Ni0.09)2O4 depended strongly on the fuel used and followed the order of aspartic acid > glutamic acid > alanine > glycine. The order of the thermoelectric characteristics was consistent with that of the density of Na(Co0.91Ni0.09)2O4. The maximal power factor (1.06 x 10(-3) Wm(-1) K(-2)) was achieved for aspartic acid-processed Na(Co0.91 Ni0.09)2O4 twice-sintered at 800 degrees C. We believe that the solution combustion route was highly effective for fabricating high-efficiency thermoelectric materials.     

钴酸盐类氧化物热电材料的研究进展

氧化物热电材料是半导体热电材料中的一种,具有独特的优点和广阔的应用前景,介绍与其研究相关的基础理论,并讨论了改善热电性能的途径.钴酸盐类氧化物中的NaCo2O4、Ca3Co4O9和Ca3Co2O6处于氧化物热电材料的研究前沿,综述了它们的晶体结构、制备方法、元素掺杂、热电性能及影响因素,探讨了其进一步的发展方向.     

钴掺杂Sr_4Fe_6O_(13)混合导体氧化物结构及透氧测定

用湿化学法合成了Ｓｒ４ＣｏｘＦｅ６－ｘＯ１３±δ系列混合导体氧化物,对其相结构与透氧性能进行了研究．钴离子的引入导致材料中钙钛矿型杂相的出现,Ｘ＝２．０时材料中还产生了ＣｏＯ杂相,ｘ＝２．６时材料呈现钙钛矿型结构．Ｓｒ４Ｆｅ４Ｃｏ２Ｏ１３±δ的相结构还与焙烧温度及环境气氛中的氧浓度密切相关．随着氧浓度的降低,材料从纯相Ｓｒ４Ｆｅ６Ｏ１３结构（纯氧气气氛下）转变为Ｓｒ４Ｆｅ６Ｏ１３结构、钙钛矿型结构和ＣｏＯ共存（空气气氛下）,直至转变为针镍矿结构、 Ｓｒ４Ｆｅ６Ｏ１３结构和 ＣｏＯ共存． Ｓｒ４Ｆｅ６Ｃｏ１３±δ导体膜在ａｉｒ／Ｈｅ氧浓差梯度下的透氧量为 １．５×１０８ｍｏｌ／ｃｍ２·ｓ（８５０℃）,在６５０～８５０℃范围内透氧活化能为７０ｋＪ／ｍｏｌ．     

固体氧化物燃料电池复合掺杂材料研究进展

概述了中温固体氧化物燃料电池要件使用的新型复合掺杂材料研究及制备进展,采用差示扫描量热法（DSC）,热重法（TG）与变温度X射线衍射对La1-xSrxMn1-yCoyO3,La1-x-zSrxCaZmN1-YCoyO3复合掺杂钙钛矿结构氧化的固相烧结合成过程进行了研究,提出了一些将来应重点研究的问题。