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1.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
2.
Lithium insertion to distorted ReO 3-type metastable solid solution Nb xW 1−xO 3−x/2 (0≤ x<0.25) has been studied by chemical and electrochemical methods. In the course of lithium insertion into tetragonal compounds, transition to a cubic phase was found to occur in the region where values of y (in Li yNb xW 1−xO 3−x/2) fall between 0.2 and 0.3, and the phase transition was found to depend on the conditions of the reaction. Changes in OCV and lattice parameters in tetragonal region ( y<0.2) were discussed from the viewpoint of the ordering of lithium ions. Also, the component diffusion coefficient of lithium in tetragonal compounds Li 0.1Nb xW 1−xO 3−x/2 (0≤ x≤0.23) was found to increase with niobium content when x≤0.10, and to saturate at 4×10 −9 cm 2/s. 相似文献
3.
By undertaking AC electrochemical impedance experiments on yttria stabilised zirconia electrolytes with polished Y 1Ba 2Cu 3O 7−x electrodes, the activation energy for oxygen ion transport within the bulk of Y 1Ba 2Cu 3O 7−x, in air, over the temperature range 823 K–1043 K, was determined to be 1.50 ± 0.05 eV. At 1000 K the oxygen ionic conductivity was calculated to be around one order of magnitude lower than that in yttria stabilised zirconia. Typical calculated values were σ=5×10 −5 (ω cm) −1 and 6×10 −3 (ω cm) −1 at the respective temperatures 823 K and 1043 K. By employing a similar cell but with Y 1Ba 2Cu 3O 7−x paste electrodes, oxygen transfer between the Y 1Ba 2Cu 3O 7−x and the electrolyte was found to occur via a surface diffusional processes. Over the temperature range 873 K–1098 K, in air, the activation energy for in-diffusion at the surface was found to be 1.4±0.1 eV and that for out-diffusion at the surface to be 1.76±0.05 eV. 相似文献
4.
Ag +/Na + ion-exchanged aluminosilicate glasses with uniform concentration profiles were prepared, and their electrical conductivities were investigated as functions of the ion-exchange ratio and the initial glass compositions. In the case of the ion-exchanged glasses of x20Ag 2O–(1− x)20Na 2O–10Al 2O 3–70SiO 2 in mol%, the conductivity, σ, and its activation energy, Eσ, showed a minimum and a maximum at the same ion-exchange ratio x=0.3, respectively, and the mixed mobile ion effect (MMIE) was observed. The fully ion-exchanged sample attained σ=3.5×10 −5 S/cm at 200 °C, which was 1.5 orders of magnitude larger than that of initial glass. In the case of x25Ag 2O–(1− x)25Na 2O–25Al 2O 3–50SiO 2, the mixed mobile ion effect was also observed at x=0.5. The maximum conductivity of 2×10 −4 S/cm at 200 °C was obtained in the fully ion-exchanged glass sample. The electric relaxation analysis was also conducted on both systems, and Kohlrausch–Williams–Watts (KWW) fractional exponent β was obtained as a function of x. The decrease of β was observed near x≈0.3 in the former system, while that of the later system was independent of the ion-exchange ratio. Based on the structural analysis results, the observed behaviors were investigated from the point of view of the occupation of Ag+ ions on the non-bridging oxygen-site (NBO-site) and the charge compensation-site (CC-site) of AlO4 tetrahedral unit. 相似文献
5.
Powder X-ray diffraction (XRD) analysis showed that the single phase perovskite-type structure of Ba 1−xLa xCe 0.90−xY 0.10+xO 3− (0
x
0.40, =0.05) could be maintained in a wide region of doping level by simultaneous partial substitution of La 3+ for Ba 2+-site and Y 3+ for Ce 4+-site in BaCeO 3. The conduction properties of these oxides were investigated using various electrochemical methods in the same concentration of oxygen vacancy ( =0.05). At high oxygen partial pressure, these oxides exhibited a mixed oxide ionic and p-type electronic conduction while at low oxygen partial pressure their conduction was almost protonic. Among these oxides, BaCe 0.90Y 0.10O 3− exhibited the highest conductivities with a value of 1.24×10 −1 S/cm in dry oxygen, and 5.65×10 −2 S/cm in wet hydrogen at 1000°C. Both of the proton and oxide ion conductivities under oxygen and under hydrogen atmospheres decreased monotonically with the increasing substitution for Ba 2+- and Ce 4+-sites. The decreases in ion conductivities appear to relate to the decreased free volume ( Vf) of crystal lattice as well as the increased distortion of lattice from ideal cubic perovskite structure. 相似文献
6.
Formation of the La 2Cu 1−xCo xO 4+δ solid solutions with orthorhombic K 2NiF 4-type structure was found to be in the range of 0≤ x≤0.30 at temperatures above 1270 K. Incorporating cobalt into the copper sublattice of lanthanum cuprate leads to increasing oxygen hyperstoichiometry and decreasing electrical conductivity. Thermal expansion coefficients of the La 2Cu 1−xCo xO 4+δ ( x=0.02–0.30) ceramics at 470–1100 K were calculated from the dilatometric data to vary in the range (12.2–13.2)×10 −6 K −1. Studying the dependence of oxygen permeation fluxes through La 2Cu(Co)O 4+δ on the membrane thickness demonstrated that the oxygen transport at the thickness values below 1 mm is limited by both surface exchange rate and bulk ionic conductivity. Oxygen permeability of the La 2Cu 1−xCo xO 4+δ solid solutions was ascertained to increase with cobalt concentration at x=0.02–0.10 and to decrease with further dopant additions, indicating a participation of interstitial oxygen in the ionic transport. 相似文献
7.
Polycrystalline (1− x)Ta 2O 5− xTiO 2 thin films were formed on Si by metalorganic decomposition (MOD) and annealed at various temperatures. As-deposited films were in the amorphous state and were completely transformed to crystalline after annealing above 600 °C. During crystallization, a thin interfacial SiO 2 layer was formed at the (1− x)Ta 2O 5− xTiO 2/Si interface. Thin films with 0.92Ta 2O 5–0.08TiO 2 composition exhibited superior insulating properties. The measured dielectric constant and dissipation factor at 1 MHz were 9 and 0.015, respectively, for films annealed at 900 °C. The interface trap density was 2.5×10 11 cm −2 eV −1, and flatband voltage was −0.38 V. A charge storage density of 22.8 fC/μm 2 was obtained at an applied electric field of 3 MV/cm. The leakage current density was lower than 4×10 −9 A/cm 2 up to an applied electric field of 6 MV/cm. 相似文献
8.
The maximum solid solubility of gallium in the perovskite-type La 1−xSr xFe 1−yGa yO 3−δ ( x=0.40–0.80; y=0–0.60) was found to vary in the approximate range y=0.25–0.45, decreasing when x increases. Crystal lattice of the perovskite phases, formed in atmospheric air, was studied by X-ray diffraction (XRD) and neutron diffraction and identified as cubic. Doping with Ga results in increasing unit cell volume, while the thermal expansion and total conductivity of (La,Sr)(Fe,Ga)O 3−δ in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7–16.0)×10 −6 K −1 at 300–800 K and (19.3–26.7)×10 −6 K −1 at 800–1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La 1−xSr xFe 1−yGa yO 3−δ ( x=0.7–0.8; y=0.2–0.4) membranes are determined by the bulk ambipolar conductivity; the limiting effect of the oxygen surface exchange was found negligible. Decreasing strontium and gallium concentrations leads to a greater role of the exchange processes. As for many other perovskite systems, the oxygen ionic conductivity of La 1−xSr xFe 1−yGa yO 3−δ increases with strontium content up to x=0.70 and decreases on further doping, probably due to association of oxygen vacancies. Incorporation of moderate amounts of gallium into the B sublattice results in increasing structural disorder, higher ionic conductivity at temperatures below 1170 K, and lower activation energy for the ionic transport. 相似文献
9.
Recently, we succeeded in fabricating single crystals of PrBa 2Cu 3O 7−δ by a modified top seeded crystal pulling method called the SRL-CP (Solute Rich Liquid-Crystal Pulling) method. Y 2O 3 and MgO polycrystalline crucibles and a MgO single crystal crucible were used to grow the single crystals. The crystal growth temperature was set in the range of 968°C to 972°C. The grown crystals were identified as PrBa 2Cu 3O 7−δ by X-ray diffraction. In the case of using Y 2O 3 crucibles the composition of the grown crystals was Y xPr 1−xBa 2Cu 3O 7−δ (0.48 < x < 0.57) and in the case of using MgO crucibles a relatively small amount of Mg contamination to the grown crystals occurred at a typical concentration of approximately 1 at.% of the sum of cations. According to the crystal growth model of the SRL-CP method [1–5], a maximum growth rate of 1.7 × 10 −5 cm/s was calculated with the aid of the phase diagram studies we reported earlier [6]. This value is reasonably in agreement with the experimental results. 相似文献
10.
A new lithium ionic conductor of the thio-LISICON (LIthium SuperIonic CONductor) family was found in the binary Li 2S–P 2S 5 system; the new solid solution with the composition range 0.0≤ x≤0.27 in Li 3+5xP 1−xS 4 was synthesized at 700 °C and characterized by X-ray diffraction measurements. Its electrical and electrochemical properties were studied by ac impedance and cyclic voltammetry measurements, respectively. The solid solution member at x=0.065 in Li 3+5xP 1−xS 4 showed the highest conductivity value of 1.5×10 −4 S cm −1 at 27 °C with negligible electronic conductivity and the activation energy of 22 kJ mol −1 which is characteristic of high ionic conduction state. The extra lithium ions in Li 3PS 4 created by partial substitution of P 5+ for Li + led to the large increase in ionic conductivity. In the solid solution range examined, the minimum conductivity was obtained for the compositions, Li 3PS 4 ( x=0.0 in Li 3+5xP 1−xS 4) and Li 4P 0.8S 4 ( x=0.2 in Li 3+5xP 1−xS 4); this conductivity behavior is similar to other thio-LISICON family with the general formula, Li xM 1−yM y′S 4 (M=Si, Ge, and M′=P, Al, Zn, Ga, Sb). Conduction mechanism and the material design concepts are discussed based on the conduction behavior and the structure considerations. 相似文献
11.
Layer-type oxide Na xM x/2IITi 1−x/2IVO 2 (M=Co, Ni; 0.60≤ x≤1.0) has been prepared by solid state reactions. In both series, two structural variants of type -NaFeO 2 (O3) and β-RbScO 2 (P2) have been obtained consecutively as x decreases with a borderline composition around xc0.7. With the decrease of x, the ionic conductivity has been found to increase up to 8.4×10 −2 S cm −1 at 770 K (Na 0.67Co 0.33Ti 0.67O 2). Compositions of P2 have been found to exhibit the conductivity values two to five times greater than those of O3, primarily due to the larger rectangular threshold available for the diffusion of Na + ions. Such a structural effect has also been considered to depend on the polarizability of alkali ion. HT-XRD and 23Na-NMR data of Na 0.67Co 0.33Ti 0.67O 2 strongly suggest that the diffusion of Na + ion is deeply related with the local distortion of trigonal prismatic sites, leading to the change of activation energy around 430 K. 相似文献
12.
The LaGa 1−x−yCo xMg yO 3−δ solid solutions with rhombohedrally-distorted perovskite structure were ascertained to form in the concentration range of 0≤ y≤0.10 at x=0.60 and 0≤ y≤0.20 at x=0.35–0.40. Increasing cobalt content results in increasing electrical conductivity and thermal expansion of the perovskites. Thermal expansion coefficients of the LaGa 1−x−yCo xMg yO 3−δ ceramics were calculated from the dilatometric data to vary in the range of 12.4–19.8×10 −6 K −1 at 300–1100 K. Doping La(Ga,Co)O 3−δ solid solutions with magnesium leads to increasing oxygen nonstoichiometry, electronic and oxygen ionic conductivity. Oxygen permeation fluxes through LaGa 1−x−yCo xMg yO 3−δ membranes were found to be limited by the bulk ionic conduction and to increase with magnesium concentration, being essentially independent of cobalt content. 相似文献
13.
The thermal expansion of Lu 2Fe 17−xSi x solid solutions has been measured by X-ray powder diffraction. The magnetic ordering in all compounds within the homogeneity range ( x3.4) is accompanied by a large spontaneous volume magnetostriction, distributed anisotropically over the principal axes of the hexagonal crystal structure. The volume effect ωs in the ground state reaches 14.7×10 −3 in Lu 2Fe 17 and decreases monotonously to 8.9×10 −3 for x=3.4, following the reduction of magnetic moment. Despite a still large ωs, the Invar behavior observed in Lu 2Fe 17 changes to a positive thermal expansion for x>1 due to an increasing Curie temperature. 相似文献
14.
The xPb(Mg 1/3Nb 2/3)O 3–(1− x)PbTiO 3 (PMNT) (with x=0.7) thin film is prepared on quartz substrates prepared using a sol–gel process. The PMNT thin film has a well-crystallized pyrochlore phase structure. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ(3) of the thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refraction index coefficient γ, the nonlinear absorption coefficient β of the thin film are 1.37×10 −12 cm 2/W and −6.73×10 −8 m/W, respectively. The real and imaginary part of the third-order nonlinear susceptibility of the film are 1.06×10 −17 and −1.65×10 −19 m 2/V 2, respectively. The results suggested that the nonlinearity is dominated by the refractive for the film. 相似文献
15.
In this paper we report studies on a range of niobate based tungsten bronzes, with a view to analysing their potential as anode materials in SOFCs. Six systems were studied, (Sr 1−xBa x) 0.6Ti 0.2Nb 0.8O 3, Sr 0.6−xLa xTi 0.2+xNb 0.8−xO 3, (Sr 0.4−xBa x)Na 0.2NbO 3, (Ba 1−xCa x) 0.6Ti 0.2Nb 0.8O 3, Ba 0.5−xA xNbO 3 (A=Ca, Sr), and Ba 0.3NbO 2.8, and the electrical conductivities were examined over a range of oxygen partial pressures (10 −20–1 bar). All the systems showed good conductivity in low oxygen partial pressures, with values as high as 8 S cm −1 at 930°C ( P(O 2)=10 −20 bar). As the oxygen partial pressure was raised the conductivity dropped showing in most cases an approximate [ P(O 2)] −1/4 dependence and good re-oxidation kinetics. Of all the samples studied the (Sr 1−xBa x) 0.6Ti 0.2Nb 0.8O 3 and (Ba 1−xCa x) 0.6Ti 0.2Nb 0.8O 3 systems appear most promising for potential use as anode materials in SOFCs. 相似文献
16.
A Bi 2V 1 − x − yU xBi yO 5.5 + 0.5x − y solid solution derived from Bi 4V 2O 11 has been prepared and characterized with x up to 0.125 for y = 0. Partial substitution of U 6+ for V 5+ in Bi 4V 2O 11 leads to the stabilization at room temperature of the high-oxide ion conducting γ-phase, in contrast with other M 6+ dopants which stabilize the β-phase. The lower conductivity in U substituted system compared with BICUVOX.10 is attributed to its higher activation energy. Conductivity values and activation energies of the U substituted phases compare well with Bi 2UO 6. 相似文献
17.
A series of apatite-type La–Ge–O ceramics were prepared and their cation-defect at the 4f+6h sites and oxide ion-defect at 2a site were investigated. In La xGe 6O 12+1.5x ceramics of x=6–12, the higher conductivities were obtained in the region of apatite composition, La x(GeO 4) 6O 1.5x−12 ( x=8–9.33), and the highest conductivity was achieved for La 9(GeO 4) 6O 1.5 ( x=9), where the number of cation (La 3+) occupying the 4f+6h sites is 9 and the number of oxide ion occupying the 2a site is 1.5. The ceramics with cation- and oxide ion-defects were La 9−0.66xSr x(GeO 4) 6O 1.5 ( x=0–1), La 9−1.33xZr x(GeO 4) 6O 1.5 ( x=0–1), La 9−xSr x(GeO 4) 6O 1.5−0.5x ( x=0–3), La 9−xZr x(GeO 4) 6O 1.5+0.5x ( x=0–1), La x(GeO 4) 3x−21(AsO 4) 27−3xO 1.5 ( x=0–3), La x(GeO 4) 33−3x(AlO 4) 3x−27O 1.5 ( x=0–3), La 9(GeO 4) 6−x (AlO 4) xO 1.5−0.5x ( x=0–3), La 9(GeO 4) 6−x(AsO 4) xO 1.5+0.5x ( x=0–1), La 9.33−xSr x(GeO 4) 6O 2−0.5x ( x=0–1.2) and La x(GeO 4) 4.5(AlO 4) 1.5O 1.5x−12.75 ( x=8.8–9.83), which were prepared by the partial substitution of La 3+and GeO 44−of the basic apatite La 9(GeO 4) 6O 1.5 with Sr 2+ or Zr 4+ and AlO 45− or AsO 43−. Such substitutions lowered the conductivity of La 9(GeO 4) 6O 1.5. These results were discussed by the electrostatic interaction between Sr 2+, Zr 4+, AlO 45− or AsO 43− and oxide ion as a conductive species. 相似文献
18.
Glass–ceramics for sealing solid oxide fuel cells (SOFCs) were developed by sintering and crystallization of the powdered glass seal. The non-isothermal sintering kinetics and crystallization kinetics were studied for four glasses in the system 50SiO 2·(45− x)BaO· xRO·5Al 2O 3 (R=Ca, Mg, Zn and x=0, 15) (mol%). Hot-stage microscopy (HSM) and differential thermal analysis (DTA) measurements demonstrated that it is possible to first sinter and then crystallize these glasses obtaining glass–ceramic seals with thermal expansion coefficients in the range 9–12×10 −6 K −1. The non-isothermal sintering kinetics was analyzed by computer simulations using a previously reported model of sintering for polydispersed glass powders which takes into account the particle size distribution, surface energy and viscosity. Good agreement was found between the measured kinetics with HSM and the calculated kinetics for all glasses. 相似文献
19.
Tracer diffusion of 18O in dense, polycrystalline La 1−xSr xCoO 3 for x = 0.1 has been measured in the temperature range 400 to 600 °C and at 500 °C for x = 0.2 at an oxygen partial pressure of 1 × 10 5 Pa. Depth profiles were obtained by secondary ion mass spectrometry. The diffusion coefficient for La 0.9Sr 0.1CoO 3 is given by D = (17–247) exp[(−232 ± 8 kJ/mole)/ RT] cm 2/s. This value is several orders of magnitude lower than D extrapolated from the results for x = 0.2 measured in the 700–900 °C temperature range. One possible explanation for the discrepancy is that the two measurements reflect different diffusion paths. As expected, La 0.8Sr 0.2CoO 3 exhibits a higher diffusivity at 500 °C than does La 0.9Sr 0.1CoO 3. 相似文献
20.
A series of LiCr xMn 2−xO 4 spinels were synthesised by the Pechini method which enables dopant Cr ions to distribute at Mn sites homogeneously. Neutron diffraction and EDS analysis confirmed that Cr ions do occupy 16d sites (octahedral intestial) evenly in the spinel structure. The Cr dopant effect improves the cyclability of spinel LiMn 2O 4 electrodes and decreases the self-discharge rate substantially. Cyclic voltammetry and AC impedance spectroscopy were employed to characterise the reactions of lithium insertion into and extraction from LiCr xMn 2−xO 4 electrodes. It was found that a thicker surface layer was formed on the surface of the pure LiMn 2O 4 electrode than on the LiMn 2O 4 electrode. 相似文献
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