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1.
G. A. Bordovskii E. I. Terukov A. V. Marchenko P. P. Seregin 《Physics of the Solid State》2009,51(11):2221-2224
On the basis of comparison of experimental and calculated parameters of the electric field gradient tensor, it is shown that holes in the YBa2Cu3O7 and YBa2Cu4O8 lattices are localized on oxygen ions in the CuO3 chains. These results agree with the model suggesting that the mechanism responsible for the high-temperature superconductivity in the YBa2Cu3O7 and YBa2Cu4O8 compounds is the interaction of electrons with two-atom two-electron copper centers with a negative correlation energy. 相似文献
2.
R. Platzer R. Schwenker A. Fuessel D.W. Tom J. Tate J.A. Gardner W.E. Evenson J.A. Sommers 《Hyperfine Interactions》1997,110(3-4):271-286
The local atomic order around very dilute indium impurities in c-axis-oriented YBa2Cu3O7 and YBa2Cu3O6.25 films at room temperature and in YBa2Cu3Ox bulk powders held in air or oxygen over a wide temperature range were investigated using 111In/Cd \gamma--\gamma perturbed angular correlation (PAC) spectroscopy. The probe atoms occupy a single substitutional lattice
position in YBa2Cu3Ox, and evidence reported here strongly supports previous claims that this is the yttrium position. In YBa2Cu3Ox powders, the local atomic order changes continuously with temperature. At room temperature the electric field gradient measured
by PAC in bulk YBa2Cu3Ox powder is indistinguishable from that in the fully oxygenated YBa2Cu3O7 film. Near the decomposition temperature, the bulk YBa2Cu3Ox powder data are semiquantitatively similar to data in the room temperature YBa2Cu3O6.25 film, with quantitative differences that we attribute to temperature averaging in the former. Other sites usually found in
PAC spectra of YBa2Cu3Ox bulk samples arise from 111In dissolved in Y2BaCuO5 and Y2Cu2O5 impurity phases. The latter phase apparently arises because of significant barium loss during processing; the barium deficiency
is clearly demonstrated by comparison of PAC data with the alloy phase diagram above the decomposition temperature. PAC data
on pure Y2Cu2O5 are reported here also.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
4.
T. M. Riseman J. H. Brewer E. J. Ansaldo P. M. Grant M. E. Lopez-Morales B. M. Sternlieb 《Hyperfine Interactions》1991,63(1-4):249-252
Zero and weak transverse fieldμ
+ SR measurements on PrBa2Cu3O
x
samples withx≈6 andx≈7 show ordered magnetism in both oxygen concentration limits. As expected for equivalent doping (nominally PrBa2Cu3O
x
∼YBa2Cu3O
x
−0.5), neither sample is superconducting. Two muon signals are observed in thex≈6 sample, as in YBa2Cu3O6, but only one (the weaker) has the same local magnetic field as in YBa2Cu3O6. In thex≈7 sample, only one site is observed; its local field is reduced with respect to that of the primary site in YBa2Cu3O6 by a factor roughly consistent with the carrier-density dependence of the Cu ion moment in antiferromagnetic YBa2Cu3O
x
. 相似文献
5.
《Solid State Communications》1999,112(5):245-249
We report on three different and complementary measurements, namely magnetization measurements, positron annihilation and NMR spectroscopy, which give evidence that the formation of oxygen vacancy clusters is the origin of the fishtail anomaly in YBa2Cu3O7−δ. In contrast to YBa2Cu3O7.0, where the anomaly is intrinsically absent, it can be suppressed in the optimally doped state where vacancies are present. Thus, clusters of oxygen vacancies rather than single vacancies or point defects are responsible for this anomaly. 相似文献
6.
Angle dependent X-ray photoemission spectra of epitaxial thin YBa2Cu3O7-x
films show characteristic differences after various heat and oxygen pretreatments. The component with the lowest binding energy in Ba 3d
5/2 and 4d
5/2 peaks results from bulk Ba in YBa2Cu3O7-x
. A component with 2 eV higher binding energy results from Ba in the surface unit cell with different bonding if compared with the bulk superconductor. This surface structure is observed for all YBa2Cu3O7-x
surfaces which have been exposed to oxygen. It is not observed for UHV prepared surfaces after mechanical scraping or fracturing. 相似文献
7.
M. Takigawa 《Applied magnetic resonance》1992,3(3-4):495-508
Results of63Cu and17O NMR experiments in YBa2Cu3O7 and YBa2Cu3O6.63 are reviewed. The normal state data revealed two important aspects of the magnetic properties of these materials, namely, the temperature dependent antiferromagnetic Cu spin correlations and the spin gap behavior, the latter being observed in the reduced oxygen material. These features appear to be the general properties of many high-T c cuprates. Anomalous temperature dependence of the anisotropy of the Cu relaxation rate was found in the superconducting state of YBa2Cu3O7, which can be explained by a d-wave pairing model. 相似文献
8.
J. H. Brewer R. F. Kiefl J. F. Carolan P. Dosanjh W. N. Hardy S. R. Kreitzman Q. Li T. M. Riseman P. Schleger H. Zhou E. J. Ansaldo D. R. Noakes L. P. Le G. M. Luke Y. J. Uemura K. Hepburn-Wiley C. E. Stronach 《Hyperfine Interactions》1991,63(1-4):177-181
A combination of μSR and17O nuclear quadrupolar μLCR has been used to obtain detailed information on the muon site in YBa2Cu3O7. The rms magnitude of the nuclear dipolar fields in YBa2Cu3O7 enriched with 38%17O is about twice that in the natural16O sample. In addition the17O μLCR spectrum shows that the electric field gradient tensor at the oxygen closest to the muon is almost equal to that measured by NMR for the CuO2 plane sites O(2,3). These results suggest that the muon in fully oxygenated YBa2Cu3O7 is located at a single site 1.0 Å from an oxygen ion, probably O(2,3). 相似文献
9.
Possible positive muon sites in YBa2Cu3O
x
were determined from the observedμ
+ hyperfine fields in antiferromagnetically ordered YBa2Cu3O
x
and GdBa2Cu3O7. After determining theμ
+ sites, the possibility of anyons or chiral spin ordering in the superconducting YBa2Cu3O7 is discussed. Positive muon implanted in YBa2Cu3O7 feel static magnetic fields of average 1.4G, which are explicable in terms of nuclear magnetic dipolar fields. Non observation
of static local magnetic fields of electronic origin (the upper limit is the order of 0.1 G) means that anyons or chiral spin
ordering might not exist in superconducting YBa2Cu3O7. 相似文献
10.
利用倾斜衬底沉积法在无织构的金属衬底上生长了MgO双轴织构的模板层,在这一模板层上实现了YBa2Cu3O7-x薄膜的外延生长.在外延YBa2Cu3O7-x薄膜前,依次沉积了钇稳定的立方氧化锆和CeO2作为缓冲层.利用X射线衍射2θ扫描、扫描、Ω扫描和极图分析测定了这些膜的结构和双轴织
关键词:
2Cu3O7-x镀膜导体')" href="#">YBa2Cu3O7-x镀膜导体
2缓冲层')" href="#">CeO2缓冲层
厚度依赖性
外延生长 相似文献
11.
Tadashi Kobayashi Hiratoshi Katsuda Yukio Sakabe Kiyoshi Iwai Seiji Kanba 《Phase Transitions》2013,86(3):215-223
EPR spectra of superconducting YBa2Cu3O7-δ and insulating Y2BaCuO5 have been examined. The intensity of Cu2+ ions in YBa2Cu3O7-δ is about 1/3000 of that in Y2BaCuO5 at room temperature. Owing to the Meissner effect in the superconducting state, the EPR signal of Cu2+ ions in YBa2Cu3O7-δ disappears; moreover the EPR signal of DPPH deposited on the YBa2Cu3O7-δ specimen is shifted. An additional EPR line is found for YBa2(Cu2.94Cr0.06)O7-δ at temperatures below 113K; this can be related to the phenomenon of superconductivity. 相似文献
12.
13.
The electric field gradients (EFGs) at all atomic positions of YBa2Cu3O7 and YBa2Cu3O6 are calculated on the basis of full potential linearized augmented plane wave calculations by an ab initio method. Cood agreement
with experimental EFGs is found for all oxygen positions in YBa2Cu3O7 and the Cu1 position in both compounds, while for the Cu2 position in the superconductor the symmetry of the EFG agrees with
experiment but the magnitude of our theoretical EFG is only half the experimental value. A small transfer of 0.07 electrons
from d(x2−y2) to d(z2) symmetry would be sufficient to achleve agreement with experiment. Thus the underlying local density approximation is not
perfect, but remains a very accurate method for describing ground state properties. 相似文献
14.
详细介绍测量高温超导体含氧量的实验方法。测定了YBa2Cu3Oy和Bi2Sr2CaCuOy两类超导体内氧的含量。发现在YBa2Cu3(1-X)Oy和Bi2(1-x)Sr2CaCu2Oy中随着Cu缺位的增大,氧的变化趋势。用X 相似文献
15.
In this paper we present a microscopic model that allows us to study the effects of charge fluctuations on the phonon dispersion of the high-temperature superconductor YBa2Cu3O7 and its insulating counterpart, YBa2Cu3O6. An ab-initio rigid-ion model with pair potentials calculated by the Gordon-Kim method from the free-ion charge densities is used as a reference system. Starting from this reference system, charge fluctuations at the copper- and oxygen ions are introduced into the model. The charge fluctuations are treated as adiabatic degrees of freedom in a non-phenomenological way. The parameters entering the model are estimated consistently with the reference system from first principles rather than refering to the experimentally determined phonon dispersion. In addition to the metallic behavior (appropriate to YBa2Cu3O7) obtained in this way, insulating behavior (appropriate to YBa2Cu3O6) is simulated by requiring the polarizability function to fulfill a corresponding long. wavelength sum rule. Screened site-potential changes are defined that (besides the charge fluctuations) constitute a qualitative measure of the electron-phonon-interaction potential. Furthermore we investigate the long-wavelength limiting behavior of the most important quantities occurring in our formalism. We derive formulae that allow us to calculate the contribution of the charge fluctuations to the macroscopic dielectric constant and the transverse effective charges in the insulating phase. 相似文献
16.
17.
A. Plecenik M. Tomasek M. Truchly M. Zahoran M. Belogolovskii S. Chromik 《Applied Surface Science》2010,256(18):5684-5687
Current-voltage characteristics of planar junctions formed by an epitaxial c-axis oriented YBa2Cu3O7−x thin film micro-bridge and Ag counter-electrode were measured in the temperature range from 4.2 K to 300 K. A hysteretic behavior related to switching of the junction resistance from a high-resistive to a low-resistive state and vice-versa was observed and analyzed in terms of the maximal current bias and temperature dependence. The same effects were observed on a sub-micrometer scale YBa2Cu3O7−x thin film-PtIr point contact junctions using Scanning Tunneling Microscope. These phenomena are discussed within a diffusion model, describing an oxygen vacancy drift in YBa2Cu3O7−x films in the nano-scale vicinity of the junction interface under applied electrical fields. 相似文献
18.
Plasma-enhanced MOCVD in which metal-organic compounds are sublimated directly into the growth chamber is studied for the first time as a new low-temperature process for growing superconducting YBa2Cu3O--x thin films. Y(THD)3, Ba(THD)2, Cu(THD)2 and oxygen are used as metal sources and oxydizing agent. Emission spectroscopy reveals that activated metal-organic compounds and activated oxygen species are present during film growth. Superconducting YBa2Cu3O7-x films whose zero-resistivity temperature are 50 K and 82 K are grown at 550°C and 600°C. 相似文献
19.
J. Niemeyer N. D. Kataria M. R. Dietrich C. Politis H. Koch R. Schöllhorn H. Eickenbusch 《Zeitschrift für Physik B Condensed Matter》1987,69(1):1-9
The ac-Josephson effect could be demonstrated up to dc voltages of 20 mV on the I–V characteristic of adjustable YBa2Cu3O7/YBa2Cu3O7 point contacts at 4.2 K. A detailed analysis of the rf power dependence of the size of microwave-induced constant voltage steps is given for microwave frequencies of 70 and 90 GHz. The results prove that electron pairing is responsible for the superconductivity in YBa2Cu3O7. 相似文献