共查询到20条相似文献,搜索用时 15 毫秒
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J. Humli
ek J. Kircher H. -U. Habermeier M. Cardona 《Physica C: Superconductivity and its Applications》1992,190(4):383-395
Ellipsometry was used to study (110) and (001) oriented films of YBa2Cu3O7 and PrBa2Cu3O7 in the mid-and near-infrared spectral regions. Below a photon energy of 0.1 eV, the in-plane component of the dielectric tensor of YBa2Cu3O7 is dominated by a Drude term with a squared plasma energy of (3.0 ± 0.3) eV2. This “oscillator strength”, and the Lorentzian broadening energy of (0.104 ± 0.005) eV at room temperature, are confirmed by the changes induced in Pr-substituted material, and by low-temperature measurements in the near-infrared. The deviation from the Drude behavior observed above 0.1 eV is accounted for by a broad absorption band with an oscillator strength of (3.6 ± 0.1) eV2 in YBa2Cu3O7 which shifts to higher energies and takes over almost all of the oscillator strength of the Drude term when Y is substituted by Pr. The response to electric fields perpendicular to the planes is much weaker, with an upper bound of 0.63 eV2 for the squared plasma energy. The in-plane loss function computed from the measured dielectric function follows the Drude-like lineshape, modified by the bound-state absorption band, down to the lowest energy reached in our measurements (0.058 eV). 相似文献
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R. Menegotto Costa L. Mendon?a Ferreira V. N. Vieira P. Pureur J. Schaf 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):107-113
We have studied experimentally the electrical magneto-conductivity near the
superconducting transition of YBa2Cu3O7-δ, YBa2
(Cu2.95Zn0.05)O7-δ and Y(Ba1.75Sr0.25)Cu3O7-δ polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to
the current orientation. The results show that the resistive transition of these systems proceeds in two stages. The pairing
transition occurs at the bulk critical temperature Tc, where superconductivity is stabilized within small and homogeneous regions of the
sample generically called grains. The regime of approach to the zero resistance state reveals the occurrence of a coherence
transition at a lower temperature Tc0. This transition is related to the connective nature of the granular samples and is controlled by fluctuations of the
order-parameter phase of individual grains. Our experiments show that the Zn-doping, besides depressing the pairing critical
temperature, strongly enlarges the temperature range dominated by effects related to the coherence transition. The substitution
of Ba by Sr causes only a small reduction of Tc, but also enhances significantly the effects related to the grain
coupling phenomenology. In general, our results indicate that these impurity substitutions in YBa2Cu3O7-δ produce or magnify the granularity at a microscopic level, enhancing the effects of phase fluctuations in the conductivity
near the transition. 相似文献
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N. G. Trusevich L. G. Mamsurova A. A. Vishnev N. B. Butko 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(3):312-314
The temperature dependences of normal state static magnet susceptibility χ(T) for high-temperature YBa2Cu3O7 superconductors (T
c ≤ T ≤ 400 K) measured for the same sample before and after 22 years of storage are compared. It is shown that during longime
storage of a maximally doped sample, its electronic system is more in equilibrium than it was in the initial state, while
a similar underdoped sample decomposed completely. Comparing the χ(T) curves for YBa2Cu3O7, we draw conclusions as to the nature of the Curie contribution and the fluctuation-induced contribution to the magnetic
susceptibility of the investigated sample, and the experimental procedure for determining T
c. 相似文献
5.
Evidence that pinning on linear or planar defects dominates the vortex dynamics in YBa2Cu3O7−x (YBCO) films is provided by complex impedance measurements at temperature 8 K<T<T
c
and magnetic field 0<B<6 T. Below the vortex lattice melting transition Bg(T) but above a threshold field Bp≈8(1-T/T
c
) T, the inductance of vortices increases as B2, much less rapidly than predicted for collective pinning of vortices by point defects. Above the vortex melting line, critical
scaling persists over the region Bg(T<B<B*(T) where the vortex correlation length ξ exceeds a characteristic length scale ξ*≡ξ(B=B*)≈450?. The value of ξ* is not sensitive to Al-doping in the Cu sites in the lattice and is close to the size of twin domains in the film. The nature
of the observed crossovers is discussed in terms of available theoretical models for a glass-liquid transition at Bg. 相似文献
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T. K. Park B. J. Mean K. H. Lee S. W. Seo K. S. Han D. H. Kim Moohee Lee H. S. Lee H. B. Kim W. C. Lee Joung-Sook Cho 《Physica C: Superconductivity and its Applications》1999,320(3-4):245-252
We have prepared Zn-substituted YBa2Cu3−xZnxO7 (YBCO, x=0.0–0.09) and performed 63,65Cu nuclear quadrupole resonance (NQR) measurements for the plane site at 300 and 100 K as a function of Zn concentration. The substitutional effects are observed in resonant frequencies and linewidths of spectra, and relaxation times as well as in the superconducting transition temperature. The spin–lattice relaxation rate 1/T1 is reduced for the higher Zn concentration and the reduction is more significant at 100 K. The ratio of 63,65Cu spin–lattice relaxation rates suggests that a magnetic contribution due to the antiferromagnetic spin fluctuation becomes weak as the Zn concentration increases. These effects confirm that the antiferromagnetic spin fluctuation of Cu 3d spins is suppressed by the Zn substitution due to the absence of local moment at the zinc site. 相似文献
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C. Trholt J.G. Wen H.W. Zandbergen Y. Shen J.W.M. Hilgenkamp 《Physica C: Superconductivity and its Applications》1994,230(3-4):425-434
YBa2Cu3O7 films in c-axis orientation on bicrystalline SrTiO3 substrates are investigated by TEM. The films and the substrates are examined in cross-section and in plane view. The grain boundary of the bicrystal substrate contains (110) faceted voids, but is otherwise straight on a nanometer scale. Contrary to this, the film grain boundary is not straight grain boundary can be up to 100 nm for a 100 nm thick film. The deviation from the intended position of the YBCO grain boundary can already occur at the film/substrate interface where it can be as much as ±50 nm. 相似文献
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A method for determination of the oxygen content (y) in YBa2Cu3O7-y films has been established, in which the lattice conetant difference (b-a) of the films was measured and used to fit the function of (b-a) vs y for the experimental data of bulk YBaaCuaO?-y given in the literature. It is suggested that the function of (b-a) vs y can indeed be used in the case of film. In this process the twin structure of the YBa2Cu3O7-y films was used. 相似文献
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A. A. Zhukov G. K. Perkins A. D. Caplin H. Kupfer T. Wolf 《Czechoslovak Journal of Physics》1996,46(Z3):1773-1774
The magnetic moments parallel and perpendicular to thec-axis (measured simultaneously) have been studied as a function of direction of applied magnetic fieldH in twinned and de-twinned YBa2Cu3O7−δ single crystals. They show pronounced anomalies when the field direction approaches thec-axis. These allow clear identification of the angle ϕL at which vortices are locked into twin planes. Complete shielding of theH
ab field component (transverse Meissner effect) was observed in the locked state. For larger angles, up to ϕT, the vortices continue to be non-collinear with the applied field, but their direction deviates from the trapping plane.
ϕL exhibits a 1/H field-dependence, whereas ϕT shows only weak logarithmic variations withH. 相似文献
13.
We have studied the penetration depth for a model of YBa2Cu3O7 involving pairing, both in the CuO2 planes and in the CuO chains. In this model pairing in the planes is due to an attractive interaction, while Coulomb repulsion induces in the chains an order parameter with opposite sign. Due to the anti-crossing produced by hybridization between planes and chains, one obtains a d-wave like order parameter which changes sign on a single sheet of the Fermi surface and has nodes in the gap. We find that our model accounts quite well for the anisotropy of the penetration depth and for the absolute values. We reproduce fairly well the whole temperature dependence for both the a- and the b-directions, including the linear dependence at low temperature. We use a set of parameters which are all quite reasonable physically. Our results for the c-direction are also satisfactory, although the situation is less clear both experimentally and theoretically. 相似文献
14.
The microstructure of the laser-ablated YBa2Cu3O7 (YBCO) thin film deposited on heated (100) SrTiO3 substrate was examined by transmission electron microscope. The par-ticles on the film mainly consist of CuO and few CuYO2. Most of these non-superconducting particles nucleate on or near the surface of the film and protrude about 100-400 nm in height, A large amount of a-axis YBCO grains also exist in the film, which nucleate at the substrate surface and grow perpendicularly above the c-axis YBCO film. The YBCO thin film deposited under low oxygen pressure has very different microstructure compared with YBCO thin film deposited under high oxygen pressure. 相似文献
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M. Jim nez-Melendo A. Domí nguez-Rodrí guez J. L. Routbort 《Physica C: Superconductivity and its Applications》1999,320(3-4):189-196
Rapid changes of oxygen partial pressure (PO2) between 103 and 2.1×104 Pa have been carried out during steady-state plastic deformation of polycrystalline YBa2Cu3O7−x (YBCO) at temperatures between 825 and 900°C. Transient creep was observed after such PO2 changes. The analysis of these creep transients allowed the determination of the chemical diffusion coefficient for reequilibration, which is identical to that found from thermogravimetry and electrical conductivity experiments for oxygen vacancies. 相似文献
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Y. Fujii H. Hamada K. Takahashi Y. Yamamoto T. Shigematsu M. Nakamura M. Yamaguchi T. Shigi 《Czechoslovak Journal of Physics》1996,46(Z3):1591-1592
The depinning temperatures in YBa2Cu3O7−δ ceramics and grains have been studied at magnetic field up to 4 T and various amplitudes of vibration. For ceramics sample,
large amplitude dependence of depinning temperature TD was observed, which indicate the decoupling of grains. In the case of a suspension sample (grain), TD was much lower than that of ceramics. 相似文献
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S. Zannella L. Jansak D. Lee K. Salama 《Physica C: Superconductivity and its Applications》1991,180(5-6):373-380
AC losses of randomly oriented and oriented grained YBa2Cu3O7−x superconductors having different microstructures and silver content were studied at 77 K and frequency range between 0.5 Hz and 60 Hz. The measurements were made by an electrical technique applying an external sinusoidal magnetic field parallel to the longer axis of the specimen. In the randomly oriented samples, the results indicate that the addition of silver has no effect on the losses of the Y-123 superconductor. Unlike the behavior of the randomly oriented samples, the oriented material does not show grain decoupling and intergranular losses and its behavior is similar to that of conventional type II superconductors. The results also show that the oriented sample has a modest surface barrier against flux entry. In general, it is found that the critical state model can be used to describe the hysteretic dissipation of Y-123 superconductors, although some refinements need to be considered. 相似文献
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This paper systematically investigates the intermediate phases of YBa2Cu3O7-x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725°C. The influence of water vapour pressure on the YBa2Cu3O7-x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40-140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture. 相似文献