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1.
Rod-shaped (Lu 1−xYb x) 3Al 5O 12 with x=0.05, 0.15, 0.30 and (Y 1−xYb x)AlO 3 with x=0.05, 0.10, 0.30 single crystals were grown by the micro-pulling-down method. Edge-defined film-fed growth method was used to prepare (Y 0.9Yb 0.1)VO 4 crystal, while Ca 8(La 1.98Yb 0.02)(PO 4) 6O 2 crystal was grown by the Czochralski method. Luminescence of these crystals was studied with main attention paid to the charge transfer emission of Yb 3+. Temperature tuned decay times in the time scale of units—tens of nanosecond was measured as a feature possibly interesting for an application in scintillation detectors in positron emission tomography. 相似文献
2.
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
3.
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
4.
Phase evolution in the Bi---Sr---Ca---Cu---Al---O system was studied. Two Al-containing phases BiSr 1.5Ca 0.5Al 2O z and (Sr 1−xCa x) 3Al 2O 6 ( x = 0.4 − 0.45) were determined to be chemically compatible with Bi 2.18Sr 2CaCu 2O 8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr 1.5Ca 0.5Al 2O z was found to be in equilibrium only with the melt and the (Sr 1−xCa x) 3Al 2O 6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr 1.5Ca 0.5Al 2O z ↔ (Sr 1−xCa x) 3Al 2O 6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr 1.5Ca 0.5Al 2O z and Bi-2212 + m(Sr 1−xCa x) 3Al 2O 6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr 1.5Ca 0.5Al 2O z phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr 1−xCa x) 3Al 2O 6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr 1−xCa x) 3Al 2O 6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content. 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.
Shaped single crystals of (Lu xGd 1−x) 3Ga 5O 12 (0.0 x1.0) and (Yb 0.05Lu xGd 0.95−x) 3Ga 5O 12 (0.0 x0.9) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu) 3Ga 5O 12 are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd 3+ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd 3+ or Yb 3+ cations below 240 nm. A complete absence of Yb 3+ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb 3+ by that of Gd 3+ ions. For specific composition of Lu 1.5Gd 1.5Ga 5O 12 an intense defect-host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi 4Ge 3O 12, was found. 相似文献
7.
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
8.
The magnetic phase diagram of La 2(Cu 1−xZn x)O 4 has been determined from zero-field muon-spin-rotation (ZF-μSR) data taken at LAMPF for 0 ≤ x ≤ 0.10. Antiferromagnetic onset temperatures follow TN( x) from susceptibility measurements on the same samples. However, the order becomes long range, as evidenced by a well-defined internal magnetic field, only at temperatures well below TN. Extrapolation of our results yields TN → 0 K at x = 0.11 for a single (Cu 1−xZn x)O 2 plane, and comparison with YBa 2(Cu 1−xZn x) 3O 6 implies identical disruption of magnetism by Zn doping in the single- and double-plane systems. 相似文献
9.
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
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.
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
12.
The n = 2 Aurivillius phase Bi 2 − xPb xSr 1 − xNd 2O 9 was successfully synthesized as a ceramic material over the whole range of simultaneous, charge compensated substitution x = 0–1.0. Structural investigations were performed by Rietveld refinement applying different space groups Fmmm and A2 1am, and additionally by X-ray absorption spectroscopy (EXAFS) on the Nd L III-edge, confirming the accommodation of Nd on the atomic sites of Sr, which implies the substitution of Bi 3+ by the isoelectronic Pb 2+. The ferroelectric transition temperature Tc = 270 °C of the substituted powders with x = 0.4 and 1.0 is distinctly reduced compared to the unsubstituted sample with Tc = 450 °C. In temperature resolved powder X-ray diffraction patterns no structural phase transition could be detected. 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.
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
15.
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
16.
We report the influence of the Sn doping on the magnetotransport properties of the LaMnO 3+δ perovskite. Two series of samples with nominal LaSn xMn 1−xO 3+δ (I series) and La (1−x)/(1+x)Sn xMn 1−xO 3+δ (II series) compositions ( x=0, 0.025, 0.05 and 0.10) were prepared at Ts=750°C. The M( T) data under 0.01 and 0.5 T for the I series reveal a depressed magnetization as the Sn content increases suggesting the presence of magnetic clusters with a superparamagnetic behavior. Resistivity measurements indicate an insulator material for all Sn content independently of the applied magnetic field. On the contrary, for the II series the M( T) and M( H) data reveal FM behavior and an improvement of the magnetization as Sn increases. These samples show magnetoresistance. The magnetotransport properties are discussed in terms of the presence of A-site cation vacancies. 相似文献
17.
The electrical property of (La 1−xSr x) 1−z(Al 1−yMg y)O 3−δ (LSAM; x≤0.3, y≤0.15 and z≤0.1) was measured using the DC four-probe method as a function of temperature (500–1000°C) and oxygen partial pressure (1–10 −22 atm). Among LSAMs, (La 0.9Sr 0.1)AlO 3−δ showed the highest ionic conductivity, σi=1.3×10 −2 S cm −1 at 900°C. A simultaneous substitution at A and B sites or A site deficiency is expected to create larger oxygen vacancy and higher ionic conductivity. However, it showed a negative effect. The effect of the vacancy increase did not effect monotonously the ionic conductivity. It was found that the concentration of oxygen vacancy, [V O], influences not only the oxide ion conductivity, σi, but also the mobility, μv, of [V O]. These properties exhibit a maximum at around [V O]=0.05. With the increase in [V O], the activation energy, Ea, of the ionic conduction dropped from 1.8 to ca. 1.0 eV at [V O]=0.05 and became almost constant at [V O]>0.05. The dependency of the pre-exponential term, μ0v, and Ea on [V O] was analyzed and their effect on μv and σi was discussed with respect to crystal structure and defect association. It was estimated that the crystal structure mainly governs these properties. The effect of defect association could not be ignored but is considered to be a complicated correlation. 相似文献
18.
A new layered cuprate compound with a nominal composition of GaSr 2Y 2−xCe xCu 2O 9−δ has been prepared. It crystallizes in a tetragonal lattice with cell parameters: a = 3.812 Å, c = 28.16 Å. The structure of the compound belongs to the same family of 1222 phase and is derived from that of GaSr 2LnCu 2O 7 by replacing the single Ln 3+ layer with a double fluorite (Y, Ce) 2O 2 layer. Like other parent cuprate compounds of superconductors, the as-prepared samples showed antiferromagnetic and semiconducting behavior. After treatment under high oxygen pressure, the samples exhibited bulk superconductivity with transition temperatures between 12–14 K. 相似文献
19.
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
20.
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
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