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1.
The lithium insertion characteristics of lithium vanadate, Li 4V 3O 8, were investigated using LiV 3O 8 prepared by the precipitation technique as the starting material. The Li 4V 3O 8 phase was formed by lithiation over x=1.5 in Li 1+xV 3O 8, and the diffusion of lithium in this phase determined the reaction rate of insertion more than x=1.5. Improvement of insertion kinetics in the Li 4V 3O 8 phase extended the lithium insertion limit from x=3.2 to x=4.0, compared with the case of LiV 3O 8 by conventional high temperature synthesis. Lithium insertion proceeds as the single-phase reaction in the range of 3.2< x<4.0. 相似文献
2.
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
3.
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
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.
Remanence, coercivity and maximum energy product ( BH) max of Nd 16Fe 76−xHf xB 8 ( x=0, 0.1, 0.2) magnets processed under different hydrogenation-disproportionation-desorption-recombination (HDDR) conditions, were studied. Vibrating sample magnetometry results showed that Hf-doped materials develop an important degree of anisotropy, especially for the case of solid-HDDR treatments at 800°C and 850°C, with the largest effect at 850°C. Maximum values of remanence and coercivity were observed for Hf-added samples S-HD at 850°C, and 900°C, respectively. The highest ( BH) max value was also observed in S-HD 900°C Hf-added samples. These results are discussed in terms of the expected microstructure of the intermediate HD and final HDDR processed powders. 相似文献
6.
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
7.
On the basis of chemical, thermal analysis and Cu K-edge X-ray absorption measurements, oxygen content in the Nd 1+xBa 2−xCu 3O z solid solution was determined between 1000°C in air and 400°C in oxygen for x=0.05–0.9 compositions. It has been observed that the oxygen nonstoichiometry Δ z of the Nd 1+xBa 2−xCu 3O 7+x/2−Δz solid solution decreases 2–2.5 times for a large substitution (Δ z≈0.3–0.33 for x=0.9), despite of the acclaimed higher total oxygen content. The difference in nonstoichiometry is explained by a higher average value of the copper oxidation state (ACV), which is vital for the solid solution with large x even at elevated temperatures (ACV≈2–2.05 for x>0.3 at 1000°C, PO 2=0.21 atm). On the contrary, the ACV after complete oxygenation is almost constant (about 2.25–2.3) for the whole series. The x-dependence of the oxygen content is not monotonous and structural phase transitions can be observed at x=0.3 and x=0.6, as confirmed by the X-ray diffraction and the Raman scattering spectroscopy. The first well-known transition is connected with the oxygen disorder due to the Nd substitution for Ba at random Ba-sites. In the present work, it is proved by the apical oxygen mode broadening in Raman spectra. Ordering of the Nd and Ba atoms with a subsequent orthorhombic distortion of the lattice may occur even at 1000°C in air due to the second transformation at x≈0.6. The invariable orthorhombicity of the Nd-rich solid solution with x>0.6 is not caused by the oxygen absorption as in the x=0.05 case. Existence of high- and low-temperature orthorhombic modifications of this solid solution has been observed for the first time. Finally, a tentative 3D ( z– x– T) diagram is suggested for the Nd 1+xBa 2−xCu 3O z solid solution up to 1000°C in air, including the new x=0.6–0.9 region. 相似文献
8.
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
9.
Ti substituted BiFe 1−xTi xO 3+δ films have been prepared on indium–tin oxide (ITO)/glass substrates by the sol–gel process. The films with x=0.00–0.20 were prepared at an annealing temperature of 600 °C. X-ray diffraction patterns indicate that all films adopt R3m structure and the films with x=0 and 0.10 show pure perovskite phase. Cross-section scanning shows the thickness of the films is about 300 nm. Through 0.05 Ti substitution, the 2 Pr increases to 8.30 μC/cm 2 from 2.12 μC/cm 2 of the un-substituted BiFeO 3 film and show enhanced ferroelectricity at room temperature. The 2 Pr values are 2.63 and 0.44 μC/cm 2 for the films with x=0.01 and 0.2, respectively. Moreover, the films with x=0.05 and 0.10 show enhanced dielectric property since the permittivity increases near 150 at the same measuring frequency. Through the substitution of Ti, the leakage conduction is reduced for the films with x=0.05–0.20. 相似文献
10.
In this study, we will develop the influences of the excess x wt% ( x=0, 1, 2, and 3) Bi 2O 3-doped and the different fabricating process on the sintering and dielectric characteristics of 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3 ferroelectric ceramics with the aid of SEM and X-ray diffraction patterns, and dielectric–temperature curves. The 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3+ x wt% Bi 2O 3 ceramics are fabricated by two different processes. The first process is that (Na 0.5Bi 0.5)TiO 3 composition is calcined at 850 °C and BaTiO 3 composition is calcined at 1100 °C, then the calcined (Na 0.5Bi 0.5)TiO 3 and BaTiO 3 powders are mixed in according to 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3+ x wt% Bi 2O 3 compositions. The second process is that the raw materials are mixed in accordance to the 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3+ x wt% Bi 2O 3 compositions and then calcining at 900 °C. The sintering process is carried out in air for 2 h from 1120 to 1240 °C. After sintering, the effects of process parameters on the dielectric characteristics will be developed by the dielectric–temperature curves. Dielectric–temperature properties are also investigated at the temperatures of 30–350 °C and at the frequencies of 10 kHz–1 MHz. 相似文献
11.
The perovskite-type oxides were synthesized in the series of Ln 1−xSr xCoO 3(Ln = Sm, Dy). The formation of solid solutions in Dy 1 − xSr xCoO 3 was limited, compared with that in Sm 1 − xSr xCoO 3. The electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C. The highest conductivity of around 500 S/cm at 1000 °C was found in Sm 0.7Sr 0.3CoO 3. The reactivity of all the samples with YSZ was examined at 800–1000 °C for 96 h. The Sr-doped perovskite oxides were more reactive with YSZ and produced SrZrO 3 at 900 °C after 96 h. However, no reaction product between SmCoO 3 and YSZ was observed at 1000 °C for 96 h. The cathodic polarization of the oxide electrodes, sputtered on yttria stabilized zirconia (YSZ), was studied at 800–1000 °C in air. SmCoO 3 shows no degradation of the electrode performance at higher temperatures. The thermal expansion measurements on the sintered samples were carried out from room temperature to 1000 °C. Large thermal expansion coefficients were found in these samples. 相似文献
12.
Samples of NbSr 2Gd 2−xCe xCu 2O y have been prepared by solid state reaction. The X-ray powder diffraction patterns show that a single phase can be formed in the composition range of 0.49< x<0.51 that has TaSr 2 (NdCe) 2Cu 2O y structure [1], the cell parameters being a=3.8669±0.0046 Å and c=28.742±0.0048 Å. Superconductivity was found by resistance measurements in the sample of NbSr 2Gd 1.5Ce 0.5Cu 2O y: the onset transition temperature is 27.4 K, and zero resistance appears at approximately 13 K. 相似文献
13.
Dielectric and pyroelectric properties of the mixed crystals system, (CH 3NH 3) 5Bi 2(1 − x)Sb 2xCl 11 (0 < x < 0.25) were systematically investigated. Temperature dependencies of ′ c in the vicinity of ferro-paraelectric phase transition were measured for the mixed crystals with x = 0.05, 0.07, 0.11, 0.13 and 0.25 in the frequency region 1 kHz–1 MHz. The substitution of bismuth atoms by antimony drastically reduces the magnitude of ′ c and shifts the ferro-paraelectric phase transition towards higher temperatures. The dielectric dispersion of the complex electric permittivity, c*, in x = 0.05 crystals was studied in the frequency range from 30 to 1000 MHz. Around 321 K phase transition, two dielectric relaxators are postulated; a low-frequency one in the megahertz region showing a critical slowing down and a high-frequency one in the gigahertz region. 相似文献
14.
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
15.
Effect of host crystallinity on lithium extraction/insertion of LiMn 2O 4 was studied. LiMn 2O 4 powders with different crystallinity were prepared via lithium-manganese-tartrates by heat treatment at various temperatures above 300 °C. First charge-discharge capacity around 4 V depended on lattice parameter a0 and lattice strain . On the other hand, the first discharge capacity around 3 V was found to be independent of these parameters. 相似文献
16.
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
17.
Enhancements of the low-field (LFMR) and high-field magnetoresistance (HFMR) were observed in the manganite system prepared by doping Nb 2O 5 into La 0.67Sr 0.33MnO 3 powders. The maximum MR ratios at 77 K with H=1 T and 1 kOe are 30% and 20% for the 0.07 molar ratio doped sample, which are 1.7 times and 1.6 times as large as that for LSMO, respectively. An MR effect up to 6.5% was also found for the sample with x=0.03 at room temperature (RT). The spin-dependent tunneling and scattering at the interfaces of grain boundaries are responsible for the LFMR while the HFMR originates from a noncollinear spin structure in the surface layer. With increasing x, the Curie temperature ( TC) decreases monotonically from 364 to 154 K while the temperature TP related to the peak resistivity decreases firstly to a minimum of 204 K ( x=0.06) and then rises up to 240 K ( x=0.1). There is a maximum resistivity ρ for the sample with x=0.06, which is higher than that for LSMO by five orders of magnitude. It is due to the enhancement of spin-dependent and independent scattering and tunneling effects on the interfaces of grain boundaries and inside the grains. 相似文献
18.
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
19.
The effects of Cu doping in MgB 2 superconductor has been studied at different processing temperatures. The polycrystalline samples of Mg 1−xCu xB 2 with x = 0.05 were synthesized through the in-situ solid sate reaction method in argon atmosphere at different temperature range between 800–900 °C. The samples were characterized through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and low temperature R– T measurement techniques for the phase verification, microstructure and superconducting transition temperature, respectively. The XRD patterns of Mg 1−xCu xB 2 ( x = 0.05) do not exhibit any impurity traces of MgB 4 or MgB 6 and they show the sharp transition in the samples prepared at 850 °C. The onset transition temperature of the prepared samples is around 39 K, which is almost the same as that for the pure MgB 2. This indicates that Cu doping in MgB 2 does not affect the transition temperature. The SEM micrograph of Mg 0.95Cu 0.05B 2 has shown that the sample is dense with grain size smaller than 1 μm. 相似文献
20.
The magnetic and crystal structures of the metallic sulfospinels Cu 0.45Co 0.55Cr 2S 4 - xSe x have been investigated for x = 0, 0.42 and 1.0 by neutron powder diffraction techniques. The data have been analyzed by the Rietveld method. All three compositions show ferrimagnetism at low temperatures with a chromium moment of (2.7±0.1)μ B and a cobalt moment of (2.8±0.1)μ B. The Curie temperature varies from 293 to 253 K. 相似文献
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