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1.
The effect of Fe 2O 3 addition (0–2.5 mol%) on the densification, crystal structure, ionic conductivity, and aging behavior of Ce 0.8Sm 0.2O 1.9 (SDC) was studied. The addition of Fe 2O 3 promotes densification, reducing sintering temperature by ~100–150 °C. X-ray diffraction showed that these materials exhibit a fluorite structure; a second phase of Fe 2O 3 is identified when Fe 2O 3 content was ≥1.5 mol%. Impedance spectroscopy measurements indicated that SDC with 0.25 mol% Fe 2O 3 has the highest conductivity, about 10% higher than that of SDC at 700 °C. Conversely, a reduction in conductivity is observed in all samples after aging in air at 800 °C for 120 h. Because of the harmful effect of aging, conductivity rapidly decreases as Fe 2O 3 content in the samples exceeded 0.25 mol%. However, SDC with 0.25 mol% Fe 2O 3 shows the same magnitude of decrease in conductivity compared with that of SDC after aging. This indicates that SDC with 0.25 mol% Fe 2O 3 continues to present the best conductivity even after high-temperature aging. 相似文献
2.
A new ternary compound Al 0.32ErGe 2 has been synthesized and studied from 298 K to 773 K using X-ray powder diffraction technique. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The ternary compound Al 0.32ErGe 2 crystallizes in the orthorhombic with the defect CeNiSi 2 structure type (space group Cmcm, a = 0.40701(2) nm, b = 1.60401(9) nm, c = 0.39240(2) nm, Z = 4 and Dcalc = 8.326 g/cm 3). The average thermal expansion coefficients , and of Al 0.32ErGe 2 are 1.72 × 10 −5 K −1, 1.11 × 10 −5 K −1 and 1.52 × 10 −5 K −1, respectively. The bulk thermal expansion coefficient is 4.35 × 10 −5 K −1. Electrical resistivity of Al 0.32ErGe 2 was measured between 5 K and 300 K. 相似文献
3.
The oxide-ion conductors (La 1−xSr x) 2Mo 2O 9−δ ( x = 0.01–0.08) were prepared by means of a conventional solid-state reaction. The effects of Sr doping for La site on the structures, electrical and thermal expansion properties of the oxide-ion conductor La 2Mo 2O 9 were investigated using X-ray diffraction, direct current four-probe method, thermal dilatometer and scanning electron microscopy, respectively. The results show that the lattice constants were first decreased, then increased, and decreased again with the increase of Sr doping content. The solid solubility of Sr in (La 1−xSr x) 2Mo 2O 9−δ is x = 0.07. The sinterability of samples is markedly improved with the increase of Sr doping content. The sintered density of sample x > 0.07 is higher than 96% of its theoretical density. When x > 0.02, doping Sr in La 2Mo 2O 9 can inhibit the excessive growth of grains, thus increases the sintered density of samples. The structural transition temperature shifts to the low side with the increase of Sr doping content, and the phase transition is completely suppressed when the doping content reaches 0.07. The conductivity of sample increases with the increase of Sr doping content. The conductivity of sample x = 0.07 reaches a maximum of 0.078 S/cm and 0.101 S/cm at 800 °C and 850 °C, respectively. In this study, it was demonstrated that doping 7 mol% Sr for La site not only can completely suppress the structural phase transition in La 2Mo 2O 9, but also can effectively enhance electrical conductivity of samples at higher temperature. 相似文献
4.
Three new series of Ho 2−xEr xMo 4O 15 ( x = 0.0–2.0), Ho 2−xSm xMo 4O 15 ( x = 0.0–0.6) and Ho 2−xCe xMo 4O 15 ( x = 0.0–0.25) solid solutions have been prepared successfully by solid-state reaction and studied by powder X-ray diffraction. All the XRD patterns of these molybdates can be indexed in monoclinic space group P2 1/ c. Lattice parameters a, b and c of Ho 2−xLn xMo 4O 15 decrease linearly with increasing erbium content and increase with increasing samarium or cerium content. Thermal expansion behaviors of Ho 2−xLn xMo 4O 15 have been investigated in the 25–500 °C temperature range with high-temperature X-ray diffraction. The temperature dependence of Mo(2)–O14 interaction looks like to be responsible for their thermal expansion behaviors. 相似文献
5.
Co-doped ceria electrolytes of Ce 0.8Gd 0.2−xY xO 1.9 ( x = 0.0–0.20) fine powders were prepared with glycine–nitrate method. The results of X-ray diffraction showed that all powders crystallite calcined at 873 K were single phase with cubic fluorite structure. The average crystallite sizes calculated by the Scherrer formula were between 21 and 23 nm, which was in good agreement with the results of TEM and particle size distribution measurements. The thermal expansion curves of Ce 0.8Gd 0.2−xY xO 1.9 were measured and the thermal expansion coefficients between 373 and 1123 K were calculated. The SEM results exhibited that electrolyte pellets sintered at 1523 K were dense, and the relative densities of these pellets were over 96%. The impedance spectra analysis of these electrolytes has been performed at 623–1023 K. The results showed that co-doped ceria exhibited higher ionic conductivity and lower activation energy than the singly doped ceria with the same dopant concentration at the temperature range of 773–1023 K, and the electrolytic domain boundary of co-doped ceria was smaller than that of singly doped ceria at 873–973 K. It suggested that co-doping with appropriate ratio gadolinium and yttrium could further improve the electrochemical performance of ceria-based electrolytes. These co-doped samples are ideal electrolyte materials of intermediate temperature solid oxide fuel cells. 相似文献
6.
This paper describes self-propagating high-temperature synthesis (SHS) of an electrolyte for solid oxide fuel (SOFC), in comparison to a conventional solid-state reaction method (SRM). Doped-lanthanum gallate: La 0.9Sr 0.1Ga 0.8Mg 0.2O 3−δ (LSGM9182) and LSGM9173 as the SOFC electrolyte, was prepared by the SHS and sintered at different temperatures, for measuring the electrical conductivity of the sintered LSGM and the power generating performance at 1073 K, in comparison to the SRM. In the SHS, the LSGM powders with smaller size were obtained and easily sintered at the 100 K-lower temperature, 1673 K, than in the SRM. Most significantly, the electrical conductivity of the sintered LSGM9182 was as high as 0.11 S cm −1 and its maximum power density was a value of 245 mW cm −2 in the cell configuration of Ni/LSGM9182 (0.501 mm in thickness)/Sm 0.5Sr 0.5CoO 3. The conclusion was that the proposed SHS-sintering method with many benefits of minimizing the energy requirement and the processing time in the production, easing temperature restriction for the sintering, and improving the electrolyte performance up to a conventional level is practicable for producing the LSGM-electrolyte of SOFC at an intermediate-temperature application. 相似文献
7.
Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95/NaCl ( x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10 −2 S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen. 相似文献
8.
Self-organized TiO 2 nanotube array was grown on titanium (Ti) thin film by anodizing in glycerol solution containing low concentration of NH 4F, and Ag/TiO 2 nanotube was then prepared from TiO 2 nanotube array by thermal decomposition. The physical properties of the synthesized TiO 2 and Ag/TiO 2 nanotubes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The synthesized two samples were used as negative materials for lithium-ion battery, and their charge–discharge property, cyclic voltammetry, electrochemical impedance spectroscopy, and cycle performance were investigated. The results indicated that the addition of Ag to TiO 2 nanotube could significantly improve the electronic conductivity, charge–discharge capacity, and cycle stability of TiO 2 nanotube. 相似文献
9.
The effects of heating-induced crystallization on the structural and mechanical properties of Mg–Ni–Fe amorphous ribbons were studied by anelastic spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction. DSC results show that the crystallization occurs through several non-reversible steps, which correspond to significant changes in the Young's modulus and concomitant irreversible elastic energy loss peaks. Moreover, an anelastic peak is found at 215 K, which for the first time indicates the presence of some dynamical process related to the simultaneous presence of different phases. The formation of a metastable Mg 6Ni phase is detected, which transforms into Mg and Mg 2Ni stable phases. A quantitative analysis of the different phases present at the different steps was also carried out. 相似文献
10.
The phase equilibria in the Y-Mn-Sn and Dy-Mn-Sn ternary systems were studied at 770 K by means of X-ray and metallographic analyses in the whole concentration range. Both Y-Mn-Sn and Dy-Mn-Sn systems are characterized by formation of two ternary compounds RMn 6Sn 6 (MgFe 6Ge 6-type, space group P6/ mmm) and R 4Mn 4Sn 7 (Zr 4Co 4Ge 7-type, space group I4/ mmm). The disorder in Dy 4Mn 4Sn 7 compound was found by single crystal method. Compounds with the same type of structure were also found with Gd, Tb, Ho, Er, Tm (confirmed), Yb, and Lu and their lattice parameters were determined. 相似文献
11.
The La 1−xK xCo 1−xNb xO 3 system was performed by conventional solid state reaction technique using metal oxides. By DSC analysis, the activation energy of crystallization of the powders with x = 0.3 is 388.4 kJ/mol. The crystal structure of the compound reveals a transition from rhombohedral to cubic, and then to orthorhombic structure as the amount of the potassium niobate (KNbO 3) increases. It is found that the structure of the samples with x < 0.3 is similar to that of lanthanum cobaltate (LaCoO 3), while at the compositions with 0.7 ≥ x ≥ 0.3, the structure transforms to cubic. Finally, with x ≥ 0.7, the structures were similar to that of KNbO 3. According to the results of selected-area-diffraction (SAD) patterns and X-ray diffraction (XRD) identifications, the lattice parameters were calculated. The direction of superlattice structure along [2 1 0] was found for x = 0.5 as identified from SAD patterns. The dielectric constants were measured with cubic structure. Dielectric constant ( K) decreases with increasing x. 相似文献
12.
In Na–U(IV)–Mo–O system, two quaternary compounds Na 2U(MoO 4) 3 and Na 4U(MoO 4) 4 were prepared by solid state reactions of Na 2MoO 4, UMoO 5 and MoO 3 in the required stoichiometric ratio at 500 °C in evacuated sealed quartz ampoules. The crystal structure of both the compounds were derived from X-ray powder diffraction data in the tetragonal system by Rietveld profile method. Na 2U(MoO 4) 3 has scheelite structure, whereas Na 4U(MoO 4) 4 has scheelite superlattice structure. TG curves of Na2U(MoO4)3 and Na4U(MoO4)4 did not show any significant weight change up to 750 °C in an inert atmosphere. During the heating cycle in an inert atmosphere, DTA curves of Na2U(MoO4)3 and Na4U(MoO4)4 showed endothermic peaks due to the melting of the compounds at 740 °C and 730 °C, respectively. Na2U(MoO4)3 and Na4U(MoO4)4, when heated in air atmosphere at 1200 °C, decomposed to form Na2U2O7 which was confirmed by weight loss calculation and XRD. 相似文献
13.
A powder X-ray diffraction investigation of the new ternary compounds Zr 6CoAs 2-type R 6MnSb 2 and R 6MnBi 2 (R=Y, Lu, Dy, Ho) is reported. The compounds Ho 6MnSb 2 ( a=0.8070(2) nm, c=0.4230(1) nm), Lu 6MnSb 2 ( a=0.7930(1) nm, c=0.4173(1) nm), Y 6MnBi 2 ( a=0.8242(1) nm, c=0.4292(1) nm), Dy 6MnBi 2 ( a=0.8211(1) nm, c=0.4286(1) nm), Ho 6MnBi 2 ( a=0.8164(1) nm, c=0.4250(1) nm) and Lu 6MnBi 2 ( a=0.8019(2) nm, c=0.4185(1) nm) crystallize in the hexagonal Zr 6CoAs 2-type structure (space group P6b2m No. 189). The Zr 6CoAs 2-type structure is a superstructure of the Fe 2P-type structure. 相似文献
14.
The crystal structure of the monoclinic phase η-Al 11Cr 2 of the space group C2/ c, a ≈ 1.76 nm, b ≈ 3.05 nm, c ≈ 1.76 nm, β ≈ 90° [L.A. Bendersky, R.S. Roth, J.T. Ramon, D. Shechtman, Metall. Trans. A 22A (1991) 5] has been determined by single-crystal X-ray diffraction. The structure model, refined to a final R value of 0.0441, has the composition of Al 83.8Cr 16.2. a = 1.77348(10) nm, b = 3.04555(17) nm, c = 1.77344(10) nm, monoclinic angle β = 91.0520(12)°. There are 80 (66Al + 14Cr) independent atomic positions in a unit cell, of which all Cr atom sites and 8 Al atom sites have icosahedral coordination. These icosahedra are interconnected forming icosahedral chains along , (1 0 1) icosahedral layer blocks as well as a three-dimensional icosahedral structure. 相似文献
15.
Nano-composite magnets with L1 0 structure derived from binary FePt alloys and prepared as melt-spun ribbons are of current interest due to their higher operating temperature and the ability to be cast as a two-phase magnet with exchange spring magnetic properties, as both soft and hard magnetic phase may emerge from the same metastable precursor, i.e. the disordered cubic A1 phase. The present paper studies the effect of Mn addition on the thermal stability and phase structure, on the abundance of the hard magnetic phase and relative proportion of the soft ones, on the microstructure of the alloy as a function of temperature and on the overall magnetic properties. The interplay of the various magnetic sublattices in the ordering of the L1 0 phases as a consequence of introducing antiferromagnetically coupled Mn atoms in the alloy composition is discussed and interpreted in terms of microstructural changes induced by this addition as revealed by high resolution transmission electron microscopy and X-ray diffraction. The temperature evolution of the phase composition and structural parameters is monitored using synchrotron radiation powder diffraction, while the compositional aspects are investigated using proton-induced X-ray emission and energy dispersive X-ray spectroscopy. Magnetic measurements reveal the magnetic parameters of interest (coercivity, remanence, Curie temperature, saturation magnetization), as well as the exchange-coupled two-phase nature of these magnets and provide information that hints at possible spin reorientation transitions in the Mn-containing planes of the L1 0 superlattice. 相似文献
16.
The crystal structure of intermetallic compound Gd 6Cr 4Al 43 has been investigated by means of X-ray diffraction data (Ho 6Mo 4Al 43 structure type, space group P6 3/ mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å). SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at TN1 = 19.0(1) K and TN2 = 6.8(1) K, respectively. 相似文献
17.
Crystal structures of R2Pd2Pb (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) compounds
The crystal structures of the R 2Pd 2Pb (R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) compounds were determined using X-ray powder diffraction. The investigated compounds crystallize with Mo 2FeB 2 structure type (space group P4/ mbm, Pearson code tP10). The importance of stabilization by polar intermetallic R–Pd bonding is underscored by a bonding analysis derived from electronic band structure calculations. 相似文献
18.
The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd 2−xY xFe 17−yGa y compounds with x = 0, 0.5, 1.0, 1.5 and y = 0, 1, 2, 3 have been investigated using X-ray and neutron powder diffractions. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th 2Zn 17-type structure with only small amounts of alpha iron. It is found that the addition of Ga atoms lessens the decreasing rates of the a-axis and unit cell volume V on the Y content but almost does not affect the decreasing rates of the c-axis. However, the substitution of Y has a positive effect on the increasing rates of the a-axis and unit cell volume V on the Ga content but has a very slight effect on the increasing rate of the c-axis. The c/ a ratio of Nd 2−xY xFe 17−yGa y as a function of Ga content exhibits a different increase for different Y content owe to the combined effects of Y and Ga on the crystallographic structure. The substitution of Y is found to have little effect on the site occupancy of Ga in Nd 2−xY xFe 17−yGa y. The combined effects of Y and Ga on the bond lengths and ASBL of Nd 2−xY xFe 17−yGa y indicate that more bonds detrimental to ferromagnetic exchange can be modulated into the desirable ferromagnetic exchange distance range through suitable combined substitution, which provides a valuable way to improve the magnetic properties of rare earth-transition intermetallic compounds. 相似文献
19.
A glass based on Y 2O 3-BaO-SiO 2-B 2O 3-Al 2O 3 (named YBA) has been investigated as sealant for planar solid oxide fuel cells (SOFCs). The YBA glass has been systematically characterized by differential thermal analysis, dilatometer, scanning electron microscopy, impedance analysis, and open circuit voltage to examine their suitability as sealant. The coefficient of thermal expansion of YBA is 11.64 × 10 −6 K −1 between 323 and 873 K. The resistivity is 9.1 × 10 4 Ω cm at 800 °C. The glass sealant is found to be well adhered with other cell components, such as electrolytes and stainless steels, at an optimum sealing temperature of 800 °C. All measured results showed that the YBA glass appears to be a promising sealant for SOFCs. 相似文献
20.
Different compositions in two solid solutions, A 2(Ti (1 − y)Zr y) 2O 7 (A = Gd 3+, Y 3+), with high oxygen ion conductivity, have been successfully prepared at room temperature via mechano-chemical synthesis. Stoichiometric mixtures of the constituent oxides were milled in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by using X-ray diffraction showing that in all cases and after milling for 19 h, the powders consisted of a single phase. Powders were also examined by scanning electron microscopy (SEM) finding out that they basically consist of sub-micron size agglomerates and aggregates of nanoparticles. 相似文献
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