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1.
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
2.
Superconductivity and crystallographic properties of La 2 − xM xCuO 4 − δ (M = Na, K) are studied. In the La 2 − xM xCuO 4 − δ system, superconductivity is detected for x 0.2. Oxygen content analysis shows that the system has more oxygen vacancies than the La 2 − xSr xCuO 4 − δ system. These oxygen vacancies may reduce the hole concentration, and high Na-doping is needed to produce superconductivity. In the La 2 − xK xCuO 4 − δ system, superconductivity is observed for the first time. Resistivity and magnetic susceptibility measurements show that Tc(onset) is 40 K and the Meissner volume fraction is about 4% for x = 0.7. The system changes from orthorhombic to a tetragonal K 2NiF 4 structure at x ≈ 0.3 and only tetragonal samples show superconductivity. 相似文献
3.
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
4.
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
5.
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
6.
Pr concentration dependence of the superconducting transition temperature Tc in the Ho 1−xPr xBa 2Cu 3O 7−δ system is determined from measurements of DC electrical resistance. This dependence coincides with that for the parallely studied Y 1−xPr xBa 2Cu 3O 7−δ reference system. Both systems have the same value of the critical concentration xc=0.58, in accordance with nearly equal ionic radii of Ho 3+ and Y 3+ ions. It has been shown that the Tc( x) curve can be described with a single mechanism based on a decreasing number of sheet holes trapped by Pr IV-ions, if one takes also into account that the number of these ions changes with x. 相似文献
7.
The polarized Raman spectra of Nd 1+xBa 2−xCu 3O 7−δ (−0.023≤ x≤0.107) and Pr 1+xBa 2−xCu 3O 7−δ (0.01≤ x≤0.15) single crystals have been investigated. It was found that the Cu(2) Ag mode softens by 6 cm −1 in Nd 1:2:3 and 4 cm −1 in Pr 1:2:3 as x increases. These frequency shifts cannot be explained by the change in the relevant bond lengths due to Nd(Pr)-substitution for Ba. The variations with x of the two low frequency modes may be affected by change of their hybridization and/or change of their force constants. The linewidths of Ba mode in Pr 1:2:3 are broader than those in Y 1:2:3. This result suggests that the Pr substitution on Ba sites occurred even in a very small value of x. In x( yy)
geometry the relative intensity of the Ba and O(4) modes in Nd 1:2:3 is greater than those in Pr 1:2:3. The difference between Nd 1:2:3 and Pr 1:2:3 in the relative intensity of the Ba and O(4) modes may be produced by the chains. 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.
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
10.
Two-dimensional-arrayed 14×14 sandwich-type junctions of Au–Pr 1−xCa xMnO 3−y (PCMO, x=0.5)–SrRuO 3 were fabricated on SrTiO 3 (0 0 1) substrates. The resistivity–voltage ( ρ–V) characteristics of each junction was measured by a two-probe method. The junctions that return to the insulating state after removing the voltage (recoverable) and the ones that remain metallic (unrecoverable) were found to co-exist in one PCMO film. The variation in the lattice constant of the PCMO film, rather than the variation of the composition, is thought to be related to the separation of recoverable–unrecoverable domains. Among several samples with a PCMO layer fabricated under various conditions, the junctions with thin PCMO layers deposited at low temperature showed a pronounced hysteresis in their ρ–V characteristics. The clear hysteresis and good crystallinity of PCMO films were correlated. 相似文献
11.
Magnetic characteristics of Ti-, Zr- and Hf-substituted PrCo 5 alloys have been studied over the temperature range from 77 to 300 K and for applied fields up to 20 kOe. It is established that Ti, Zr and Hf substitute for Pr. Single-phase materials are formed for all values of x up to 0.2 in the system Pr 1−xZr xCo 5 but for x only up to 0.1 for Pr 1−xTi x Co 5 and Pr 1−xHf xCo 5 alloys. Larger amounts of Zr can be substituted if the material is made hyperstoichiometric in Co, e.g., Pr 0.7Zr 0.3Co 5.5. All the alloys show a decrease in magnetic moment and an increase in Curie temperature as x increases. Anisotropy fields decrease as x increases at 295 K. Anomalous behavior is observed at 77 K, suggested that these ternary alloys may have a cone structure at this temperature. 相似文献
12.
Structure and magnetic properties of the Zr 1−xMn xCo 2+δ alloys were studied for 0 x <0.7, δ=0, 0.45. The cubic C15 Laves phase structure shows Mn solubility up to x≈0.4. The other Laves phase with the hexagonal C36 structure found for x0.5 apparently has a small region of Mn solubility in the vicinity of Zr 0.4Mn 0.6Co 2. Though the parent Mn-free compounds are known to be paramagnetic, the Mn-substituted alloys show ferromagnetic behavior with the Curie temperatures up to 625 K and the room-temperature saturation magnetization of about 100 emu/g. The onset of ferromagnetism with the Mn substitution for Zr may be caused by polarization of itinerant 3d electrons, like it was earlier supposed for the off-stoichiometric ZrCo 2+δ. The universal composition dependencies of the intrinsic magnetic properties for different δ can be obtained, if plotted against the amount of zirconium atoms missing in its sublattice. The room-temperature anisotropy with the noticeable anisotropy field of 24 kOe and the 1 1 0 easy magnetization direction laying in a basal plane was found in the hexagonal Zr 0.5Mn 0.5Co 2. 相似文献
13.
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
14.
Cation deficient spinels Ni xMn 3−x□ 3δ/4O 4+δ (0≤ x≤1) have been prepared by thermal decomposition of mixed oxalates Ni x/3Mn (3−x)/3(C 2O 4)· nH 2O in air at 623 K. They have been characterised by temperature programmed reduction (TPR) under H 2, the reaction being followed by gravimetric and powder X-ray diffraction measurements. It has been shown that TPR proceeds in several steps. The first steps correspond to the loss of nonstoichiometric oxygen leading to the formation of a stoichiometric oxide. During the following stages the manganese cations are reduced, causing the spinel structure to be destroyed, and the formation of solid solution of NiO in a cubic MnO. Subsequently, Ni 2+ cations undergo a reduction to metallic nickel, and, finally, a mixture of nonstoichiometric MnO 1−δ and metallic nickel is formed. These oxides contain a high level of vacancies which vary with the nickel content with a maximum of δ≈1 near x=0.6. This nonstoichiometry is ascribed both to the presence of Ni 3+ and excess of Mn 4+. 相似文献
15.
New Scheelite-related solid solutions of the compositions Na x/2Bi 1−x/2Mo xV 1−xO 4 (0≤ x≤1) and Bi 1−x/3 Mo xV 1−xO 4(0≤ x≤0.2) have been synthesised by the substitution of Na and Mo at the A and B sites respectively of the ABO 4 type ferroelastic BiVO 4. The phases were characterised using chemical analysis, powder X-ray diffraction, scanning electron microscopy, EDAX, and Raman spectroscopy. While almost a continuous solid solution is obtained for the series Na x/2Bi 1−x/2Mo xV 1−xO 4, the absence of Na at the A-site results only in a narrow stability region for the other series, Bi 1−x/3 Mo xV 1−xO 4 where 0≤ x≤0.2. Raman spectra of selected samples at room temperature also suggest that vanadium and molybdenum atoms are disordered at the tetrahedral sites. 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.
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
18.
Defect structures of the lanthanum-substituted PbWO 4 prepared by mechanical alloying (MA) were investigated by means of powder neutron diffraction and FT-IR, to compare with that of the oxide ion conductive sintered samples. Neutron diffraction revealed that Pb 1−xLa xWO 4+x/2 prepared by MA possessed the lead site deficiency in the lattice. In addition, it was also found that occupation factors of the lead site were still smaller than the nominal value even for the mechanically alloyed Pb 1−xLa 2x/3WO 4. The vacancy formation at the lead site of the mechanically alloyed Pb 1−xLa xWO 4+x/2 was also corroborated from the splitting of the absorption band around 800 cm −1 ascribed to the W–O stretching vibration of WO 4 tetrahedron. At the end of this paper, the formation process of the lead site vacancy was discussed in the sintered Pb 1−xLa xWO 4+x/2 during milling. 相似文献
19.
Samples of Li 1 − zNi 1 + xO 2 with various x values were synthesized and their electrochemical properties, phase transitions, and ordering phenomena were investigated comparatively. In order to synthesize samples with a small x value, an excess lithium was used as a starting material to compensate for lithium loss during the calcination process. A stoichiometric sample with a large reversible capacity of more than 200 mAh g −1 is also described. 相似文献
20.
The nucleation mechanism to predict coercivity values in melt-spun exchange-coupled (Nd 1−xPr x) yFe 94−yB 6 alloys for various Nd:Pr ratios x, and Fe:RE ratios y, was tested using the dependence of the anisotropy constant K1 on Pr content x for the minimum nucleation field HNmin in the modified Brown's equation. Very good agreement was found between experimental data and theoretical values, confirming the predominance of the nucleation of reverse domains over the wall pinning process in the coercivity mechanism of melt spun REFeB alloys. 相似文献
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