共查询到20条相似文献,搜索用时 15 毫秒
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Yu Mei C. Jiang S. M. Green H. L. Luo C. Politis 《Zeitschrift für Physik B Condensed Matter》1987,69(1):11-16
A systematic study has been carried out on the normal state resistivity of YBa2Cu3O7–x
. Samples were cut from the same well-annealed material and were quenched from different temperatures (T
Q
). The resistivity is metallic whenT
Q
500 °C and becomes semiconductor-like whenT
Q
600 °C. The data on the latter was interpreted in terms of the three-dimensional localization model proposed by Mott.The work at USCD was supported by the California MICRO program 相似文献
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Temperature dependencies of acoustic lossesQ
–1 and of relative sound velocity change v/v in YBa2Cu3O7– up to 60 K are calculated by the tunneling model theory. The tunneling systems are related to the off-centered positions of the apical oxygen atoms O(A) and are described through the pseudo-Jahn-Teller effect. Tunneling systems' parameters are distributed in narrow range of values and are in correspondence with the experimentally observed infrared phonon spectra and thermal ellipsoids of O(A). Respective relaxation times are calculated by the adapted reaction rate method. The calculatedQ
–1(T) and v(T)/v dependencies are in good agreement with the experimental data, which is an additional support to the conclusion about the existence of tunneling systems in YBa2Cu3O7– due to the pseudo Jahn-Teller effect. 相似文献
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Temperature dependences of the resistivity tensor components ρab and ρc were measured for YBa2Cu3O7?x single crystals with different oxygen contents. The resistivity anisotropy ρc/ρab was found to grow exponentially with decreasing temperature. The results are compared with the predictions of different models describing transverse transport in the normal state of cuprate high-T c superconductors. 相似文献
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We have measured the resistivity of the YBa2Cu3O7–Ag composite system with Ag volume fraction,p
Ag ranging from 0–100%. The percolation behavior and the normal-state resistivity are studied. We find a three-dimensional threshold for the Ag matrix occurring atp
Ag 20% and a threshold for the superconducting matrix occurring at 1–p
Ag30%. The electrical resistivity is interpreted in terms of a resistivity model for granular YBa2Cu3O7 proposed by Halbritter et al. [Z. Phys. B —Condensed Matter71, 411 (1988)]. Based on this model, we show that the resistivities between the YBa2Cu3O7 grains and flaws in the grains are greatly diminished in the samples, indicating significantly improved grain growth behavior of the YBa2Cu3O7 phase resulting from the addition of Ag. With the diminishing of the grain boundary resistivities, an intrinsic value for the temperature coefficient of resistivity, (1/gr)(d/dT), can be inferred, which is 3.3×10–3/K at 300 K. This value is very close to that observed in the Cu–O2 planes in single crystals and epitaxial films of YBa2Cu3O7. 相似文献
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介绍掺硅对YBCO超导态及正常态性质的影响。在所研究的掺硅浓度范围内发现电阻温度转变曲线有二次转变台阶。 相似文献
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By measuring magnetic torque moment in a field-sweeping process, the temperature and field dependence of the critical current density j (with a criterion of electric field) and the normalized relaxation rate Q = d lnj/d ln E of a YBa2Cu3O7-δ thin film were obtained. With a minimum current density (jmin = 10A·cm-2) the irreversibility lines at different sweeping rates were determined. It was found that these irreversibility lines cannot be fitted to either the melting line or the vortex-glass transition. All the data can be interpreted by the thermally-assisted-flux-flow model. Further investigation shows that, at irreversible tem-perature and field, Uc is much smaller than kBT, which indicates that the thermal depinning is the real origin of the irreversibility line. 相似文献
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This paper presents systematically the doping effects of halogens in YBa2Cu3O7-δ polycrystalline samples, with a series of concentrations of fluorine, chlorine, bromine or iodine. All samples were prepared by chemical method of citrate pyrolysis, which makes the halogen concentration in the samples more uniform. Samples doped with F have Tc as high as 94.5K, Cl, Br and I dopings also raise Tc to a certain extent. In addition, the influence of halogen doping on critical current density, morphology, constitution and so forth is discussed. 相似文献
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Crystals of YBa2Cu3O7-δ (YBC) were prepared using a flux technique. The as-grown crystals were typically on the order of 200 μm × 200 μm × 50 μm, where the 50 μm dimension is in the c-direction. Ferroelastic behavior was observed by applying a uniaxial stress along the [100]tet-direction using a specially-designed fixture which was mounted to a programmable hot/cold stage of a polarizing reflected-light microscope. Domain wall motion was observed for temperatures greater than 200°C, and complete poling was accomplished at stresses on the order of 50–100 MPa at temperatures of 350–400°C. An ionic diffusion-activated mechanism is suggested. 相似文献
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高临界温度氧化物超导体的发现,对超导电性研究领域、凝聚态物理、以至整个物理学和其它相关学科、高新技术的发展,已经并正在继续产生着深远的影响。高温超导体中元素替代研究有着其特殊的意义。例如,通过元素替代,已发现了多种结构类型的几十种新的高温氧化物超导 相似文献
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We report the results of our microchemical analyses of low- large-angle grain boundaries in bulk YBa2Cu3O7- using nanoprobe energy-dispersive-X-ray spectroscopy (EDX) and electron-energy-loss spectroscopy (EELS). We observed periodic variation in the concentration of Cu along the boundaries, and oxygen depletion at the boundaries. We found that the chemistry of the grain boundary is very sensitive to grain boundary dislocations (GBDs), while, in turn, the configuration of the GBDs is very sensitive to the boundary misorientation and the boundary plane normal. The strain field associated with closely spaced GBDs reduced the density of mobile holes at the boundary, which is expected to be detrimental to the superconducting properties of the boundary. The possible structural transition of the grain boundaries from an oxygen-deficient state to a fully oxygenated state near a coincidence orientation is discussed, based on the reduction of the elastic strain energy of the boundaries. 相似文献
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In order to obtain insight into the role played by the phonons in the superconducting phase transition, we have performed infrared reflectivity and inelastic neutron scattering experiments on single phase YBa2Cu3O7–(0.1,T
c
=94 K, T
10–90=1 K). These experimental results, together with published Raman scattering and specific heat data are used to determine the parameters of a rigid-ion model; the model is able to reproduce qualitatively the experimental data. On the basis of our model we derive and discuss the phonon density of states and the pattern of atomic displacements of some important vibrational modes. In particular, the model reveals the existence of high-frequency oxygen breathing modes and of low-frequency copper dimerization modes in both the CuO3-chains and the CuO2-planes. Furthermore, Jahn-Teller like oxygen modes exist in the chains. The possible role of these modes with respect to the pairing mechanism is discussed. In addition there exist low-frequency chain-degrading modes which favour jumps of oxygen atoms out of the CuO3-chains into neighbouring vacant sites in the basal plane. 相似文献
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《Solid State Communications》1987,63(9):843-846
We report measurements of the far-infrared reflectivity of polycrystalline samples of YBa2Cu3O7-δ which have their superconducting transition temperatures in the 90 K range. The measurements performed between 300 K and 10 K reveal temperature-dependent structures attributed to optical phonons in the 150 cm-1 – 350 cm-1 range, and excitation of the electrons across the energy gap. Complicated structures make unambiguous fitting with the Mattis-Bardeen theory difficult, but it seems that the energy gap is around 3.5 kTc for T⪡Tc. Additionally, our results indicate the possibility of a second gap at an energy corresponding to 5.4 kTc. 相似文献
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本文介绍了一种用于合成平均尺寸小于1μm的超细YBa2Cu3O7-δ(Y-123)粉末的固态反应法。合成Y-123粉末的传统方法是利用BaCO3、Y2O3和CuO粉末直接固态烧结反应。本文介绍的方法则利用BaCuO2(011)、Y2O3和CuO粉末之间的固态反应。本方法不包括传统反应法中限制反应速率的BaCO3分解反应,因而与传统固态反应法相比,其合成温度及保温时间大大降低,从而可以合成超细粉末。将011、Y2O3和CuO粉末按4:1:2的摩尔比混合后在900℃于流通氧气中烧结15小时,此时反应刚好完成而生成的Y-123粉末又不过分长大,得到的粉末平均尺寸小于1μm。 相似文献
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E. Zepezauer A. Kalbeck S. D. Ganichev W. Korzenietz W. Prettl 《International Journal of Infrared and Millimeter Waves》2000,21(3):355-363
A novel approach to intrinsic Josephson-detection of far infrared radiation is reported utilizing near-zone field effects at electric contacts on c-axis oriented YBa2Cu3O7- films. While only a bolometric signal was observed focusing the radiation far off the contacts on c-axis normal films, irradiating the edge of contacts yielded an almost wavelength independent fast signal showing the characteristic intensity dependence of Josephson-detection. The signal is attributed to a c-axis parallel component of the electric radiation field being generated in the near-zone field of diffraction at the metallic contact structures. 相似文献