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1.
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
2.
The Co-sublattice anisotropy in Lu 2Co 17 consists of four competitive contributions from Co atoms at crystallographically different sites in the Th 2Ni 17-type of crystal structure, which result in the appearance of a spontaneous spin-reorientation transition (SRT) from the easy plane to the easy axis at elevated temperatures. In order to investigate this SRT in detail and to study the influence of Si substitution for Co on the magnetic anisotropy, magnetization measurements were performed on single crystals of Lu 2Co 17−xSi x ( x=0−3.4) grown by the Czochralski method. The SRT in Lu 2Co 17 was found to consist of two second-order spin reorientations, “easy-plane”–“easy-cone” at TSR1≈680 K and “easy-cone”–“easy-axis” at TSR2≈730 K. Upon Si substitution for Co, both SRTs shift toward the lower temperatures in Lu 2Co 16Si ( TSR1≈75 K and TSR2≈130 K) with the further onset of the uniaxial type of magnetic anisotropy in the whole range of magnetic ordering for Lu 2Co 17−xSi x compounds with x>1 due to a weakening of the easy-plane contribution from the Co atoms at the 6g and 12k sites to the total anisotropy. 相似文献
3.
An attempt is made to synthesize Nd 2Co 14C compound by mechanical alloying Nd 16Co 76B 8−xC x (0 x8) alloys and subsequent annealing. Phase formation and magnetic properties of Nd 2Fe 14B-type Nd 16Co 76B 8−xC x alloys and their hydrides are investigated. The Nd 2Co 14(B,C) phase with Nd 2Fe 14B-type structure is formed for Nd 16Co 76B 8−xC x (0 x7) alloys, while NdCo 7C δ phase with TbCu 7-type structure is observed in Nd 16Co 76C 8 alloy. The lattice parameter c of the Nd 2Co 14(B,C) phase decreases with increasing the carbon content. A limit volume of the unit cell to form the Nd 2Fe 14B-type structure is estimated to be 0.870 nm 3. The spin-reorientation temperature TSR increases with increasing the carbon content, due to an enhancement of magnetocrystalline anisotropy caused by carbon substitution for boron. After hydrogenation, the lattice expansion is observed for Nd 16Co 76B 8−xC x (0 x7) alloys. The spin-reorientation temperature of Nd 16Co 76B 8−xC xH y (0 x7) is much lower than that of the host alloys. Some structural and magnetic properties of hypothetic Nd 2Co 14C and Nd 2Co 14CH y compounds are estimated by extrapolation. 相似文献
4.
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
5.
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
6.
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
7.
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
8.
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
9.
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
10.
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
11.
The structural and ferroelectric characteristics of SrBi 2(Nb 1−xW x) 2O 9 ( x=0–0.12) ferroelectric ceramics were investigated. SrBi 2(Nb 1−xW x) 2O 9 ceramics consisted of a single-phase layered perovskite structure when x was less than 0.06. Uniform microstructure and grain size reduction were observed after the introduction of W. The maximum remanent polarization of 16 μC/cm 2 appeared at x=0.03, and the coercive field decreased with increasing concentration of W. The ferroelectric behavior of SrBi 2(Nb 1−xW x) 2O 9 ceramics is interpreted based on the Raman measurement. 相似文献
12.
The results of the impedance spectroscopy measurements on eutectic samples based on zirconium oxide are presented here. Samples of CaZrO 3---ZrO 2(cubic) and MgO---ZrO 2(cubic) have been grown by a directional solidification procedure such that the different phases appear nearly oriented along the growth direction (lamellae in the system of CaZrO 3-ZrO 2(cubic) and fibers of MgO in a ZrO 2 matrix in the other system). The DC electrical conductivity has been measured by impedance spectroscopy along and across the growth axis. For CaZrO 3---ZrO 2 the coductivity is clearly anisotropic. The following values for σ T have been obtained: the conductivity at 600 °C equals 2.0 × 10 −6 Ω −1 cm −1 perpendicular to the fiber axis and 1.4 × 10 −5 Ω −1 cm −1 parallel to it and with an activation energy of 1.3 eV for σ T. For MgO---ZrO 2(cubic) the isotropic value of the conductivity at 600 °C is 10 −4 Ω −1 cm−1 with activation energy for σ T of 1.5 eV. The anisotropic conductivity in the CaZrO 3---ZrO 2 (cubic) system has been explained by a model of an ordered stacking of oxygen conducting (cubic ZrO 2) and non-conducting (CaZrO 3 or MgO) phases. 相似文献
13.
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
14.
Low-field negative magnetization, of the order of −10 −1 emu/g-Oe, from 4.2 K up to room temperature and higher (350 K), and coercive-field magnetization reversal are both present in Cr (3−x)Fe xX 4 for X=S, Se, Te and x=0 to 3, and for Cr 5Te 8 and Cr 7Te 8. For Cr 2FeSe 4 the zero-field-cooled (ZFC) magnetization is negative for 5 Oe and below. To obtain a more detailed knowledge of the magnetic phases involved in the observed magnetization versus temperature M( T) curves, we obtained and studied neutron diffraction (n.d.) scans on the compound Cr 2FeSe 4, taken at 14 temperatures from 4.2 to 300 K. For this same n.d. sample, the temperature for magnetization reversal of value −3×10 −4 emu/g-Oe is 80 K in 40 Oe applied field, then the reversal disappears for 65 Oe applied field. The complex magnetic interactions responsible for this reversal are revealed in the hysteresis curves. 相似文献
15.
The structural and superconducting properties of single-phase Fe-substituted La 2.5Nd 0.5CaBa 3(Cu 1−xFe x) 7O z (LNCBCuFe) with 0.0 x0.06 compounds having triple-perovskite structure are investigated using X-ray diffraction, a.c. susceptibility, d.c. magnetization, oxygen content and Mössbauer effect measurements. Mössbauer spectral analysis of x=0.03 sample displays unusual Fe-dopant site occupancies and the Cu(2) plane to Cu(1) chain site ratio in the LNCBCuFe are quite different from those of the usual Fe-doped YBa 2Cu 3O 7−δ. Specifically, we observe substantial occupation of a new chain-associated quasi-octahedral site, E, at 300 K which transforms into the well-known distorted tetrahedron chain site, A, on lowering the temperature to 78 K. The observed reduction of Tc with increasing x in LNCBCuFe supports the view that the hole filling mechanism contributes predominantly to the suppression of superconductivity by Fe. 相似文献
16.
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
17.
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
18.
Iron/iron-oxide granular films were fabricated using reactive dc magnetron sputtering. Their structural, magnetic and transport properties were systematically studied. XPS and TEM confirmed the coexistence of Fe, FeO and Fe 2O 3. A metal–insulator transition was observed with the increasing of the oxygen component in the film. The temperature dependencies of longitudinal resistivity ρxx and anomalous Hall resistivity ρxy were discussed. We found the enhancement of ρxy and investigated the scaling law between anomalous Hall coefficient Rs and ρxx. In all the samples, Rs was found to be proportional to ρxx when ρxx is small, which indicated the skew scattering is dominant. 相似文献
20.
The lithium intercalation into the layered dichalcogenide 3R-WS 2 has been investigated by electrochemical reduction and by chemical reaction in n-butyl lithium solution. Essential results are (a) a charge transfer of nearly 0.6e −/W in Li xWS 2, (b) a small increase of the c-axis parameter of about 0.6%, and (c) a high mobility of the Li +-ions. The chemical diffusion coefficient of Li +-ions is estimated to be 8 × 10 −9 cm 2 s −1 in the composition range 0 ≤ x ≤ 0.25. The appearance of a structural transformation from 3R-WS 2 to 2H-Li xWS 2 is interpreted on grounds of instabilities in the interlayer structure. 相似文献
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