Pr1－xSrxAlO3－δ的合成及其作为固体氧化物燃料电池阴极的性能研究

采用固相反应法合成了一系列样品Pr_1－xSr_xAlO_3－δ (x＝0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5). XRD结果表明, Sr在A位上的固溶度约为20%; 利用交流阻抗法测量了样品的电导率, 结果表明, 电导率随着Sr掺入量的增加而增大, Pr_0.8Sr_0.2AlO_3－δ的电导率最大, 在850 ℃达到0.02 S/cm; 离子迁移数的测试结果说明, Pr_1－xSr_xAlO_3－δ为离子电子混合导体; 考察了它们作为固体氧化物燃料电池(SOFCs)阴极的性能, 极化曲线和阻抗的测试结果表明, 阴极性能随着Sr掺入量的增加而提高; 阴极稳定性测试结果表明, 在测量时间范围内, 阴极过电位随时间缓慢下降.     

Low temperature heat capacities of mechanically alloyed La-doped PbWO4 system

Heat capacity measurements were carried out on Pb_1-xLa_xWO_4+x/2 (x=0.2) and Pb_1-xLa_2x/3WO₄ (x=0.2, 0.5) solid solutions prepared by sintering and mechanical alloying (MA) methods. For all the solid solutions, sintered samples showed slightly larger heat capacity around 100 K in comparison with MA samples, which was presumably caused by the excitation of mobile oxide ion motion. For sintered scheelite-type structured PbWO₄s, high-temperature synthesis introduced oxide ion interstitials even for the Pb_1-xLa_2x/3WO₄ system, which resulted in the excess heat capacity at low temperature for excitation. On the other hand, for the samples prepared by room-temperature MA technique, oxide ion seemed to occupy the regular sites rather than interstitial ones and excess heat capacities were not observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crystal structure and electrical conductivity of cubic fluorite-based (YO1.5) x (WO3)0.15(BiO1.5)0.85- x (0?≤ ?x ≤?0.4) solid solutions

(WO₃)_0.15(BiO_1.5)_0.85 exhibits a tetragonal structure derived from the fluorite subcell. The electrical conductivity of (WO₃)_0.15(BiO_1.5)_0.85 is lower than that of Y₂O₃-doped Bi₂O₃. The structure and electrical conductivity of samples formulated as (YO_1.5) _x (WO₃)_0.15(BiO_1.5)_{0.85- x} (x = 0.1, 0.2, 0.3, and 0.4) were investigated. The as-sintered (YO_1.5)_0.1(WO₃)_0.15(BiO_1.5)_0.75 exhibited a single cubic structure that is isostructural with δ-Bi₂O₃. For x = 0.2, 0.3, and 0.4, the as-sintered samples consisted of a cubic fluorite structure and rhombohedral Y₆WO₁₂. After heat treatment at 600 °C for 200 h, the cubic structures are stable for x = 0.1, 0.3, and 0.4. A transformation from cubic to rhombohedral phase after heat treatment at 600 °C for 200 h was observed in the sample originally formulated as (YO_1.5)_0.2(WO₃)_0.15(BiO_1.5)_0.65.     

Thin films of Ln1−xSrxCoO3 (Ln=La, Nd and Gd) and SrRuO3 by nebulized spray pyrolysis

Thin films of La_1−xSr_xCoO₃, Nd_0.5Sr_0.5CoO₃, Gd_0.5Sr_0.5CoO₃ and SrRuO₃ have been deposited on Si(100), LaAlO₃(100) and SrTiO₃(100) single crystal substrates by nebulized spray pyrolysis. The films deposited on Si are generally polycrystalline, but they are highly oriented on the oxide substrates. The cobaltate films are generally not metallic, but exhibit low resistivity specially when x=0.3 and 0.5, the latter also exhibiting ferromagnetic characteristics. Films of La_0.7Sr_0.3CoO₃ show negative magnetoresistance of 35% around 180 K. Films of SrRuO₃ are metallic on Si and LaAlO₃ substrates but show an insulator–metal transition on SrTiO₃ around 130 K, around which temperature negative magnetoresistance is observed.     

Electrophysical and electrochemical properties of Y1 − x Ca x Cr1 − y Me y O3 (Me = Mg, Cu)

Structure, thermal elongation coefficient, and conductivity of Y_{1 ? x} Ca _x Cr_{1 ? y} Me _y O₃ (Me = Mg, Cu) in air are studied at 100–1000°C. Electrochemical activity of electrodes made of most conducting compositions Y_{1 ? x} Ca _x Cr_{1 ? y} Me _y O₃ (Me = Mg, Cu), contacting solid electrolyte 0.9ZrO₂ + 0.1Y₂O₃, is studied over a wide range of polarizations, in air, at 700–900°C.     

Oxygen ionic transport in Bi2O3-based oxides: II. The Bi2O3–ZrO2–Y2O3 and Bi2O3–Nb2O5–Ho2O3 solid solutions

Electrical conductivity, fluorite-type cubic unit cell volume and thermal expansion of the (Bi_{1− x} Nb _x )_{1− y} Ho _y O_1.5+δ (x=0.05 and 0.08; y=0.10−0.15) and (Bi_{1− x} Zr _x )_{1− y} Y _y O_1.5+δ (x=0.05 and 0.07; y=0.15) solid solutions have been found to decrease regularly with increasing dopant content. Annealing at temperatures below 900 K leads to a phase decomposition and to a sharp decrease in conductivity of the ceramics. Oxygen ion transference numbers have been determined by the e.m.f. method and by Faradaic efficiency measurement to exceed 0.9. A new technique of studying Faradaic efficiency has been proposed and verified using (Bi_0.95Zr_0.05)_0.85Y_0.15O_1.5+δ and Zr_0.90Y_0.10O_1.95 ceramic samples. Received: 31 October 1997 / Accepted: 18 December 1997     

Co-cation conduction in solid electrolytes based on AAlO2 (A = Li, Na)

Regions of the formation of tetragonal solid solutions with the γ-LiAlO₂ structure and the co-cation conduction are studied in the systems 0.9Na_1-xLi_xAlO₂-0.1EO₂ (E = Ti, Ge, Si) and 0.8Na_1-xLi_xAlO₂-0.2TiO₂. The single-phase regions of solid electrolytes narrows down with decreasing size of cations of a rigid lattice. No polyalkaline effect exists in the above systems. In the single-phase region of solid solutions, variations in the conductivity is caused largely by variations in the partial conductivity of the more mobile sodium cation.     

Chemical Stability,Ionic Conductivity of BaCe0.9−xZrxSm0.10O3−α and Its Application to Ammonia Synthesis at Atmospheric Pressure

Dense ceramic samples BaCe_0.9?xZr_xSm_0.10O_3?α (x=0.10, 0.15, 0.20, 0.30) were obtained by heat‐treating the precursors prepared from a coprecipitation route. The phase structure, chemical stability and conduction behaviors of the ceramic samples have been investigated by X‐ray powder diffraction and alternating current impedance spectroscopy methods. All the ceramic samples displayed a single phase of orthorhombic perovskite. The samples with x≧0.20 were relatively stable after exposed to the flowing mixed gases: CO₂ +H₂O+N₂ at 873 K for 12 h. Among the samples tested, the sample with x=0.20 exhibited both adequate conductivity and better chemical stability. The contribution of different charged species for x=0.20 sample to the conduction in wet hydrogen atmosphere was investigated by means of gas concentration cells. It was found that the sample of x=0.20 was almost a pure ionic conductor, and the ionic conduction was contributed mainly by proton and partially by oxide ion in wet hydrogen atmosphere at 773–1073 K. The ammonia synthesis at atmospheric pressure in an electrolytic cell based on the sample of x=0.20 was successfully conducted and the peak ammonia formation rate achieved 2.67×10^?9 mol·s^?1·cm^?2 with direct current of 0.80 mA at 773 K.     

Magnetic susceptibility studies of Mn1-xMxO (M = Zn, Mg, Fe)

Magnetic susceptibility studies of Mn_1-xM_xO (M = Zn, x≤0.1; M = Mg, x≤0.12;M = Fe, x≤0.4) in the range 77 to 300 K are reported. The methods of preparation of Mn_1-xM_xO systems preclude the presence of trivalent ions. The M_1-xFe_xO system shows anomalous behaviour aroundx = 0.2–0.3. The results are discussed in terms of competition between the nearest neighbour and the next-near-neighbour interactions, dilution effects and cooperative effects of FeO₆ octahedra.     

Structural and Magnetic Properties of Bi(Fe1-xMnx)O3

Bi(Fe_1-xMnx)O₃ bulk ceramics with Mn concentration x up to 0.3 were prepared by rapid sintering using sol-gel derived fine powders. Structure transformation is found to depend on the Mn doping concentration by X-ray diffraction and Raman spectroscopy. Bi(Fe_1-xMnx)O₃ maintains the rhombohedral structure of BiFeO3 with x=0.05 and 0.1, but changes to the orthorhombic structure with x=0.3. Weak ferromagnetism is observed for Bi(Fe_1-xMnx)O₃ with x=0.05 and 0.1, but stronger paramagnetism is observed for Bi(Fe_1-xMnx)O₃ with x=0.3 indicating a magnetic phase change from antiferromagnetic to paramagnetic with the structure changing from R3c to C222. Two anomalies at 30 and 140 K are observed for Bi(Fe_1-xMnx)O₃ with x=0.05 and 0.1. The anomaly at 30 K is concluded to be related to the freezing of cluster spin glass from dc magnetic memory and relaxation measurements.     

Y2SiO5:Ce3+荧光体的基质多面体替换及其对发光性能的调控研究

荧光材料基质的结构调制对于调控发光材料的发光性能,探索固体结构-性能关系具有重要的研究意义。本文以Y2SiO5基质为模型,分别利用Si/Al和Si/P取代,以[AlO4]和[PO4]四面体替换[SiO4]四面体,设计合成了一系列组成为Y1.95Si1-xAlxO5-xFx∶0.05Ce3+(x=0.05,x=0.1,x=0.2,x=0.4,x=1)和Y1.95-yCaySi1-yPyO5∶0.05Ce3+(y=0,y=0.02,y=0.04,y=0.06,y=0.08,y=0.2)的荧光材料。结合X射线衍射、荧光光谱、荧光寿命等测试手段对其进行了表征分析。结果表明,在x≤0.2,y≤0.04时得到的产物能够保持Y2SiO5的结构特征,在一定的基质组成替换范围内,设计合成的样品Y1.95Si1-xAlxO5-xFx∶0.05Ce3+、Y1.95-yCaySi1-yPyO5∶0.05Ce3+能提高发光强度,发射光谱呈现蓝移现象。荧光寿命测试表明这两个系列的化合物中Ce3+所处的基质环境变化较小,Ce3+发光也未产生较大的变化。     

Role of rhodium doping into lanthanum cobalt oxide (LaCoO3) perovskite and the induced bifunctional activity of oxygen evolution and reduction reactions in alkaline medium

Transition metal oxides, especially perovskites, have been considered effective electrocatalysts for the oxygen evolution (OER) and oxygen reduction (ORR) reactions in an alkaline solution. Here, a series of lanthanum cobalt rhodium oxide perovskites with the chemical formula LaCo_1-xRh_xO₃ (LCRO, 0.1 ≤ x ≤ 0.70) were prepared through the approach of solid-phase synthesis and their bifunctional electrocatalytic activity was assessed for both the OER and ORR. The crystallinity, morphology, surface, and electrocatalytic features of the LCRO were significantly correlated with the rhodium content. The LaCo_0.7Rh_0.3O₃ electrocatalysts with x = 0.3 showed enhanced electrocatalytic bifunctional performance with a substantially lower OER/ORR onset potential of 1.38/0.73 V vs HRE, smaller Tafel slope (116/90 mV/dec), and low charge-transfer resistance, which is the most efficient catalyst among the other studied ratios and superior to the pristine lanthanum cobalt oxide benchmark electrocatalysts. The LaCo_0.7Rh_0.3O₃ electrode exhibit good bifunctional electrocatalytic behavior and long-term durability with an OER and ORR onset potential gap (ΔE = E_OER ? E_ORR) of only 0.65 V, which could be credited to the enriched oxygen vacancies, lattice expansion and the improved electrical conductivity upon the doping of larger size of Rh ions. The LaCo_1-xRh_xO₃ catalysts are obtained from abundant materials that have the potential of highly-active bifunctional OER and ORR electrocatalysts.     

Structure and Magnetism of Pr1−xSrxFeO3−δ

Crystal structure, redox, and magnetic properties for the Pr_1−xSr_xFeO_3−δ solid-solution phase have been studied. Oxidized samples (prepared in air at 900°C) crystallize in the GdFeO₃-type structure for 0≤x≤0.80, and probably in the Sr₈Fe₈O₂₃-type (unpublished) structure for x=0.90. Reduced samples (containing virtually only Fe³⁺) crystallize as the perovskite aristotype for x=0.50 and 0.67 with randomly distributed vacancies. The Fe⁴⁺ content increases linearly in the oxidized samples up to x≈0.70, whereupon it stabilizes at around 55%. Antiferromagnetic ordering of the G type is observed for oxidized samples (0≤x≤0.90) which show decreasing Néel temperature and ordered magnetic moment with increasing x, while the Néel temperature is nearly constant at 700 K for reduced samples. Electronic transitions for iron from an average-valence state via charge-separated to disproportionated states are proposed from anomalies in magnetic susceptibility curves in the temperature ranges 500–600 K and 150–185 K.     

Sol-gel formation and properties of nanocrystals of solid solutions Y1 − x Ca x FeO3

Nanopowders of ferrites Y_{1 ? x} Ca _x FeO₃ (x = 0.1, 0.2, and 0.3) were prepared by chemical coprecipitation of cations Y³⁺, Ca²⁺, and Fe³⁺ by an aqueous sodium carbonate solution. It was found that an increase in the calcium content leads to a decrease in the size of nanocrystals, the average size of which is 25–50 nm. Doping of yttrium orthoferrite with the doubly charged calcium ion enhances magnetization and decreases coercivity in samples.     

La1-xSrxFeO3钙钛矿型氧化物中的晶格氧用于甲烷部分氧化制合成气

采用燃烧法制备了Sr掺杂钙钛矿型氧化物La_1-xSr_xFeO₃（x=0,0.3,0.5,0.9）载氧体,对载氧体分别进行X射线衍射、扫描电镜和H₂程序升温还原反应表征,在热重循环装置和固定床反应装置上考察甲烷与载氧体晶格氧的部分氧化反应.结果表明,La_1-xSr_xFeO₃氧化物中的晶格氧适用于甲烷部分氧化制合成气,晶格氧的得失是一个可逆过程,Sr的掺杂提高了载氧体的供氧能力,5次循环后载氧体得失晶格氧的能力没有明显的衰减.从甲烷转化率、n（H₂）/n（CO）比以及H₂和CO的选择性等方面来考虑,x=0.3-0.5比较理想,甲烷转化率维持在70%左右,气体产物中n（H₂）/n（CO）约为2,CH₄没有发生明显的裂解.     

Structural, magnetic and dielectric properties of Sc modified (1 − y)BiFeO3–yBaTiO3 ceramics

In this study, the bulk ceramics with general formula (1 − y)BiFe_1−xSc_xO₃–yBaTiO₃ (x = 0.1–0.3, y = 0.1–0.3 mol%) were prepared by the traditional solid-state method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that all samples crystallized in pure perovskite structure. The structural phase transition from R3c to Pm-3m occurred when the amount of BaTiO₃ exceeded 20 mol%. The room temperature M–H curves were obtained and scandium doping could decrease the magnetic coercive field. Thus the soft magnetic property of prepared solid solutions could be improved. Frequency dependence of dielectric constant and loss were studied. The results indicated that addition of an appropriate amount of scandium could reduce the dielectric loss. The dielectric losses of 0.7BiFe_1−xSc_xO₃–0.3BaTiO₃ (x = 0, 0.1, 0.2, 0.3) at 1 kHz were 0.104, 0.094, 0.043 and 0.057 respectively.     

Determination of yttrium and lanthanum in zirconium dioxide by HPLC, X-ray fluorescence and neutron activation analyses

Summary Lanthania-and yttria-stabilized zirconium oxide ceramics have been examined using High Performance Liquid Chromatography (HPLC), thermal neutron activation (NA) and X-ray Fluorescence (XRF) analyses and thus determine the stabilizer content. Ceramic powders with the composition ZrO₂:x mol % La₂O₃ (x=5, 10, 15, 20 and 33) and ZrO₂:x mol % Y₂O₃ (x=10, 15, 20 and 25) were prepared by the citrate and the co-precipitation techniques, respectively. The lanthanum content was determined by HPLC (x=5.09, 9.78, 14.98, 19.81 and 25.94) and NA (x=5.15, 10.32, 17.25, 21.08 and 27.97) analyses, the yttrium content by HPLC (x=8.5, 13.5, 17.9 and 22.1) and XRF (x=9.9, 15.8, 20.1 and 24.9) analyses. An experimental sequence, based on continuous dilution of ceramic powder solutions, is proposed for preparing samples for HPLC measurements. A swimming pool nuclear reactor is used for NA analysis. The quantitative determinations of yttrium and lanthanum doping levels obtained using those techniques are described.     

Effects of dopant concentration and aging on the electrical properties of Y-doped ceria electrolytes

High purity cerium oxide and yttrium oxide were used to form ceria-based solid solution (Ce_1−xY_xO_2−δ, 0.05x0.4) via a conventional mixed-oxide method. All the samples used were aged at 1000 °C in air for 8 days. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ionic conductivity (i.e., grain interior (GI) grain boundary (GB) and total conductivities) in this system were systematically studied as a function of dopant content over the temperature range of 250–850 °C in air using an impedance spectroscopy. The lattice parameter decreased with increasing the Y content, but it did not obey Vegard's law. The Y doping had no significant effect on densification behavior and final sintered density, but leading to a significant decrease in grain size as compared to the undoped ceria. The composition x0.1 had a maximum GI conductivity, while a maximum total conductivity was observed at x0.15. A significant high-temperature aging effect was also found for the samples with higher Y doping levels. 10% and 15% decreases in the GI and GB conductivities, respectively, were detected in the aged Ce_0.7Y_0.3O_2−δ ceramic.     

CeAlO3 and Ce1−xRxAlO3 (R=La, Nd) solid solutions: Crystal structure, thermal expansion and phase transitions

The crystal structures of CeAlO₃ and the solid solutions Ce_1−xR_xAlO₃ (R=La, Nd), and their thermal behaviour in a wide temperature range of 12−1200 K have been precisely determined by means of in situ high-resolution X-ray powder diffraction technique applying synchrotron radiation, thermal analysis and magnetic measurements. The unique sequence of the reversible phase transitions I4/mcm↔Imma↔R3¯c↔Pm3¯m has been detected in CeAlO₃ and solid solutions formed in the pseudo-binary system CeAlO₃-LaAlO₃. In the Ce_1−xNd_xAlO₃ system, the samples with x=0.3 and 0.5 compositions undergo three phase transformations I2/m↔Imma↔R3¯c↔Pm3¯m, whereas for the Ce-rich sample Ce_0.9Nd_0.1AlO₃ four successive transitions are observed: I4/mcm↔I2/m↔Imma↔R3¯c↔Pm3¯m. Crystal structure parameters of all structural polymorphs of CeAlO₃ and solid solutions based on them as well as their thermal evolution are reported. Based on in situ powder diffraction and DTA/DSC data, the phase diagrams of the pseudo-binary systems CeAlO₃-LaAlO₃ and CeAlO₃-NdAlO₃ are constructed together with a combined phase diagram, where the transition temperatures are presented as a function of the average radius of rare-earth cations.     

Structural Transition and Magnetic Property of Bi1-xYbxFeO3

Bi_1-xYb_xFeO₃(0≤x≤0.2) powders have been synthesized using a sol-gel method. The X-ray diffraction data show a structural transition from the rhombohedral R3c phase to the orthorhombic Pnma phase between x=0.1 and 0.125, which should induce a ferroelectric- paraelectric transformation. The phase transition is also proven by the Raman spectroscopy. A moderate signal on magnetization appears to illustrate the enhancement of magnetization at the transformation boundary, which is suggested to be the destruction of the spin cycloid structure at low concentration. The appearance of antiferromagnetic ordering is proposed to account for the afterward reduction of the magnetization at high concentration.