共查询到20条相似文献,搜索用时 562 毫秒
1.
Tsuyoshi Yoshioka Tomoyuki Yamamoto Akihiko Kitada 《Physica B: Condensed Matter》2012,407(21):4114-4116
The valence state of Co ions in Pr1−xCaxCoO3−δ and Pr1−xSrxCoO3−δ has been investigated by an analysis of the Co-L3 X-ray absorption near-edge structure (XANES) profile. The observed intensity distributions of Co-L3 XANES change continuously with increasing concentration of alkaline-earth ions. To investigate the origin of this change in the XANES profile, charge transfer multiplet calculations were carried out, which could successfully explain the change in the spectral profile; they also suggest that the valence state of Co ions in Pr1−xCaxCoO3−δ and Pr1−xSrxCoO3−δ is between 3+ and 4+ and increases gradually with the concentration of alkaline-earth ions. 相似文献
2.
Ca3−xErxCo4O9+δ (x=0, 0.05, 0.15, 0.3 and 0.5) samples were prepared using a sol-gel method followed by hot-pressing sintering technique. Powder X-ray diffraction analysis showed the single-phases of Ca3−xErxCo4O9+δ were obtained up to x=0.3 and the crystallinity of the samples decreased with increasing Er-doping amount. The high-temperature (323-1073 K) thermoelectric properties of the samples were investigated. The substitution of Er3+ for Ca2+ resulted in the decrease of electrical conductivity, thermal conductivity and the increase of Seebeck coefficient for all the samples except the x=0.05 one. The dimensionless figure of merit ZT reached 0.28 at 1073 K for Ca2.7Er0.3Co4O9+δ, indicating the thermoelectric properties of CaCo4O9+δ can be enhanced by doping Er in the system. 相似文献
3.
We have magnetically and structurally characterized the Ho1−xSrxCoO3−δ family of materials where 0.67≤x≤0.95. The solid solution range and evolution of the structure as a function of x is established and correlated with the broad range of magnetic behavior observed. The structure is shown to be tetragonal I4/mmm although is possibly cubic when x=0.95. For 0.67≤x≤0.9 the material shows antiferromagnetic long range order and ferromagnetic clusters. At x=0.95 the magnetic transition is at 120 K and the imaginary susceptibility becomes non-zero and the temperature of the cusp in the ac susceptibility shows a frequency dependence indicative of glassiness. 相似文献
4.
A series of La-substituted M-type Sr hexaferrite powders Sr1−xLaxTi0.05Zn0.2Fe3+11.75O19, wherein x ranges from 0.1 to 0.5 with a step of 0.1, have been prepared by the conventional ceramic method and were then milled in a high energy mill to prepare nanosized powders. XRD investigation of the calcined and the milled powders shows that single phase hexaferrite structure has been formed after calcining and has not changed after milling. The lattice parameters and the mean crystallite sizes of the samples have been determined from the XRD data and Scherrer's formula. The results show that the lattice parameters (“а” and “c”) decrease with increase in La-substitution and the mean crystallite size of the milled powders is about 17 nm. Coercivities and magnetizations of the samples in a magnetic field of 16 kOe have been determined from the room temperature hysteresis loops. It was found that both parameters increase with La substitutions up to 0.3 and then decrease for higher substitutions. These variations were attributed to the enhancement of hyperfine field and spin-canting magnetic structure when La content increases. In addition, the magnetizations were smaller for the nanosized samples in comparison with those of bulk ones, which were discussed according to the core-shell model. Also the results show that annealing of the nanosized samples up to 500 °C can enhance coercivity and magnetization of the samples, which is discussed based on crystallite size growth. 相似文献
5.
We present our recent results on the temperature dependence of current-voltage characteristics for polycrystalline Y1−xPrxBa2Cu3O7−δ superconductors with x=0.0, 0.1 and 0.3. The experimental results are found to be reasonably well fitted for all samples by a power like law of the form V=R(I−Ic)a(T). Here, we assume that a(T)=1+Φ0IC(T)/2πkBT and IC(T)=IC(0)(1−T/TC)3/2 for the temperature dependences of the power exponent and critical current, respectively. According to the theoretical interpretation of the obtained results, nonlinear deviation of our current-voltage characteristics curves from Ohmic behavior (with a(TC)=1) below TC is attributed to the manifestation of dissipation processes. They have a characteristic temperature Tp defined via the power exponent as a(Tp)=2 and are related to the current induced depinning of Abrikosov vortices. Both TC(x) and Tp(x) are found to decrease with an increase of Pr concentration x reflecting deterioration of the superconducting properties of the doped samples. 相似文献
6.
Zhifeng Wang Nansheng Xu Weizhong Ding Fushen Li 《Journal of Physics and Chemistry of Solids》2011,72(1):50-55
Perovskite compounds in the system of SrCo1−xFexO3−δ (x=0.2, 0.4 and 0.6) were synthesized by solid state reaction. SrCo1−xFexO3−δ shows the p-type small polaron conduction behavior. Electrical conductivity and oxygen vacancy content decrease with increase in Fe content. The incorporation of Fe increases the structural stability of SrCo1−xFexO3−δ at low temperatures, while decreasing the structural stability at high temperatures. Oxygen partial pressure has a strong influence on electrical conductivity. At low oxygen partial pressure, SrCo0.8Fe0.2O3−δ will transform from cubic to orthorhombic structure. This structure can remain in 5%H2/Ar only for a short time and then dissociates into Sr3Fe2O6.64 and Co due to the reduction of B-site elements. 相似文献
7.
M. Veverka P. Veverka O. Kaman K. Kní?ek E. Pollert 《Journal of magnetism and magnetic materials》2010,322(16):2386-2389
Nanoparticles of the single spinel phase Co1−xZnxFe2O4+γ of mean size 3-23 nm, as determined by X-ray diffraction analysis, were synthesized by the co-precipitation method followed by a temperature treatment. Magnetic studies carried out in the range of 4.5-550 K revealed gradual transition from ferrimagnetic to superparamagnetic to paramagnetic behaviour depending on the composition and particle size. The observed behaviour indicates a broad distribution of volume sizes of the nanoparticles. Particular importance can be ascribed to the composition of x=0.6 where the observed transition temperature to the paramagnetic state at 310-334 K suggests applicability of this material for magnetic fluid hyperthermia in a self-controlled regime. 相似文献
8.
J.J. Cheng 《Journal of Physics and Chemistry of Solids》2011,72(5):585-588
We have investigated the magnetic and transport properties of borocarbide superconductors YNi2B2C and YPd5B3C0.4 with Yttrium partially substituted by Samarium. The upper critical fields HC2 are determined by the scaling analysis of the thermal fluctuation magnetoconductivity. Around the transition region, the thermal fluctuation magnetoconductivity can be scaled by a universal function for all applied magnetic fields. The formula HC2(T)=HC2(0)[1−(T/TC)3/2]3/2 of a narrow-band pairing mechanism gives an excellent fit to the value of upper critical field HC2(0)=7.6 T in the Y0.8Sm0.2Pd5B3C0.4 compound. The superconducting coherence length ξ is determined to be 6.58 nm, the Ginzburg-Landau parameter κ is 29 and the penetration depth λ is 191 nm. 相似文献
9.
The perpendicular magnetic anisotropy (PMA) and magnetization in Pt1−δFeδ/Co (δ=0, 0.017, 0.04 and 0.06) multilayer films have been investigated. It is found that, on adding a small amount of Fe into the Pt layers, Pt/Co multilayer films maintain well-defined PMA at both 5 and 300 K along with significantly enhanced magnetization even at room temperature, which is far greater than the Curie temperature of Pt1−δFeδ dilute alloys. Further study demonstrates that the large enhancement of the magnetization in the Fe doped Pt/Co multilayers at 300 K arises from the bulk moment of the Pt1−δFeδ layers at the interface region, where the ferromagnetic order persists up to room temperature due to the strengthened exchange interactions between Fe atoms via strongly polarized Pt near the Pt1−δFeδ/Co interfaces. For the Pt0.96Fe0.04/Pt multilayers, the magnetically ordered region in each Pt0.96Fe0.04 layer extends over at least 10 Å from the interface at room temperature. 相似文献
10.
Piotr A. Gauden 《Applied Surface Science》2010,256(17):5285-5291
The problem of the estimation of high resolution comparative plots (αs method) is revised. Adsorption isotherms of Ar (T = 87 K) are simulated (GCMC) on the bundles of closed and opened multiwalled carbon nanotubes. Those materials are chosen in order to observe the influence of porosity on Ar adsorption, and consequently, on the comparative plots. The introduction of the structural heterogeneity (defects in the external and internal walls of osculating and separated nanotubes) is also studied. The monolayer and multilayer parts of adsorption are extracted from the total amount adsorbed for all studied adsorbents and the reference one (the bundle of the ideal 3-layered carbon tubes with very wide diameters). The significant influence of the distance between carbon nanotubes and defects (in the external and internal walls) is observed on the monolayer αs-plots. In the case of comparative plots calculated for the multilayer adsorption the differences are also visible; however, the expected linear dependence of the amount adsorbed on a porous solid plotted against the amount adsorbed on a reference nonporous solid (the layer-by-layer adsorption occurs on both solid surfaces) in a wide range of relative pressures is not observed. The obtained results demonstrate the complexity of αs method when both microporosity and surface heterogeneity are present. A comparison of isotherms shows that for the studied adsorbents Ar is sensitive to the appearance of the geometrical and structural defects, even at low coverage. 相似文献
11.
Superconducting Ba1−xKxBiO3−δ pellets were synthesized by solid state reaction followed by sintering. Thermo-gravimetric and differential thermo-gravimetric analysis (TG-DTA) of the mixture of nitrates was carried out to study the reactions during the phase formation. The effect of different sintering temperatures on the phase formation was studied. The X-ray diffraction data confirms the formation of superconducting Ba0.6K0.4BiO2.23 phase at 700 °C. The surface morphological studies as a function of sintering temperature were studied by SEM. It is observed that the pellets prepared by solid state reaction followed its sintering at 700°C shows the superconducting transition at 26.8 K. 相似文献
12.
The solid electrolyte Ce1?xCaxO2-?x with the fluorite-type structure (Ca-doped CeO2) is a mixed conductor. Conduction occurs predominantly by migration of O2? ions via oxygen vacancies or by electrons, depending on the departure from stoichiometry. The ionic transference number σi/σi + σe was determined as a function of dopant concentration (0.07?x?0.15), temperature (400–800°C), and oxygen pressure by emf measurements with oxygen concentration cells. It is described by The entropy term S1(x) changes from 38.7k for x = 0.07 to 31.7k for x = 0.15; the enthalpy term, 5.42 eV, is independent of x and in excellent accord with semi-empirical calculations. 相似文献
13.
Zhaofei Li Jun Tang Masanori Watahiki 《Journal of Physics and Chemistry of Solids》2010,71(4):495-1635
We have successfully synthesized the α-FeSex binary tetragonal superconductors with nominal composition of FeSex (x=0.6-1.0) via conventional solid state reactions between Fe and Se sealed in quartz tubes. Fe and β-FeSe are the most commonly seen impurities in this binary system. A low-temperature annealing at 400 °C is found to be crucial to remove β-FeSe, which is the thermodynamic stable phase with hexagonal symmetry. For all the samples of FeSex, superconductivity is confirmed by magnetic measurements as well as resistivity measurements with their Tc at around 8 K. We noticed that their Tc does not vary with the different nominal Se amount. High-resolution synchrotron X-ray diffraction analysis revealed that the unit cell parameters of all these samples do not change within the error range, and their structure only tolerate the same very small amount of Se deficiency. Based on this study, we concluded that the α-FeSex superconductor only exist in a very narrow deficiency range. 相似文献
14.
The absolute vibrational numbering of the Na2b3Πu state has been established by direct observation of the v = 0–13 levels. These b3Πu levels appear as the lower levels in rotationally resolved fluorescence spectra resulting from OODR excitation of 3Πg, 3Δg, and 3Σg+ states via b3Πu ~ A1Σu+ mixed intermediate levels. The molecular constants for the Na2b3Πu state are (in cm?1, one standard error in parentheses)
13 517.2 (1.3) | 0.1434 (0.0027) | |||
153.6 (1.1) | 9×10?5 (4×10?4) | |||
0.47 (0.09) | 3.20 (0.03) Å | |||
7.85 (0.60) | 0.19 (0.16) |
20195.23 | 29.10 | 0.00891 | 5.340733 | |
(1) | 13913.42 | 18.44 | 0.00781 | 5.697722 |
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