共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Steiner V. Kinsinger I. Sander B. Siegwart S. Hüfner C. Politis 《Zeitschrift für Physik B Condensed Matter》1987,67(1):19-23
XPS and UPS photoemission experiments on the highT c superconductors (T c ≈90 K) with nominal composition YBa2Cu3O9-y (y≈2) show the following:
- The density of electronic states at the Fermi energy is very small, much smaller than in pure Cu.
- The Cu 2p spectra show only a Cu2+ contribution.
- The Ba core levels show a structure with two components of nearly equal magnitude, which leads to the suggestion that these compounds have large O2? vacancies coordinated to Ba2+ sites.
- Annealing at 400°C under UHV conditions leads possibly to a partial reduction of Cu2+ to lower Cu valence states and to a small increase of the O2? vacancy component of the Ba2+ line.
2.
C. Politis J. Geerk M. Dietrich B. Obst H. L. Luo 《Zeitschrift für Physik B Condensed Matter》1987,66(3):279-282
We report the synthesis, characterization and superconducting temperature of high-temperature superconducting Y0.3Ba0.7CuO3, Y0.4Ba0.6CuO3 and Y1.2Ba0.8CuO4. The volume fraction of the superconducting phase is estimated to be of the order of 10%.HighT
c
superconductivity withT
c
-onsets up to 125 K (midpoint 102 K, zero resistance: 90 K) is observed in multi-phase Y–Ba–Cu–O oxygen defect compounds with the nominal composition of Y1.2Ba0.8CuO4–y
(0y0.4). 相似文献
3.
4.
A. D. Semenov 《Journal of Experimental and Theoretical Physics》1999,89(3):552-558
This paper reports on an investigation of transient photoimpedance response to radiation, in other words, real-time variations
of the impedance induced by femtosecond optical pulses in superconducting films transferred to the mixed state by an external
magnetic field applied parallel to the c-axis. When the films were in a state characterized by the absence of dc resistivity, the response amplitude increased with the magnetic field faster than expected owing to the contribution of magnetic
vortices to the impedance of a superconductor with s-wave pairing of electrons. It turned out that the effect is due to a growth in the effective density of quasiparticle states
in the mixed state of a d-wave superconductor. In the absence of magnetic field, however, the response amplitude was higher at lower temperatures,
which contradicts the predictions of both models. Possible reasons for this feature in the response as a function of temperature
are discussed.
Zh. éksp. Teor. Fiz. 116, 1035–1047 (September 1999) 相似文献
5.
M. Ohshima S. Hayashibe N. Kawamura Y. Itoh M. Fujioka T. Ishimatsu 《Hyperfine Interactions》1979,7(1):103-107
We have determined theg-factor of the 2140.2 keV 5– state of136Ba using the timeintegral perturbed angular correlation (IPAC) method at an external magnetic field of 17.0 kG;g=–0.38±0.04. The half-lives of the 2140.2 keV 5– and 2207.1 keV 6+ states were redetermined to be 1.5±0.1 ns and 3.1±0.1 ns, respectively. The radioactive source of136Cs was prepared by the138Ba(, pn) reaction. 相似文献
6.
K. Sreedhar R. A. Mohan Ram A. K. Raychaudhuri P. Ganguly C. N. R. Rao 《Phase Transitions》2013,86(1-2):3-15
High-temperature superconductivity in the Y-Ba-Cu-O system has been discussed with special reference to the identification and characterization of the pure monophasic compound responsible for the superconductivity. The crucial role of oxygen has been examined in the light of the structure and thermogravimetric analysis. 相似文献
7.
P. Steiner S. Hüfner V. Kinsinger I. Sander B. Siegwart H. Schmitt R. Schulz S. Junk G. Schwitzgebel A. Gold C. Politis H. P. Müller R. Hoppe S. Kemmler-Sack C. Kunz 《Zeitschrift für Physik B Condensed Matter》1988,69(4):449-458
From XPS core level spectroscopy the average copper charge on the Cu sites in the high temperature superconductor Y1Ba2Cu3O7–x
is determined as function of the oxygen vacancy concentrationx. Analysis of these data leads to the suggestion that there are holes on the oxygen sites in the basal plane of the crystal structure. The probability for holes on these oxygen ions is rather constant for 0x0.3 with a value of 0.64 and decreases to zero forx=0.5. The dependence of the superconducting transition temperature on the hole concentration is discussed. An energy level diagram for Cu2+ and Cu3+ in YBa2Cu3O7–x
is constructed. 相似文献
8.
S. Sato S. Horii J. Shimoyama H. Ogino K. Kishio 《Physica C: Superconductivity and its Applications》2010
Superconducting properties have been systematically studied for oxygen content controlled Y2Ba4O7O15?δ (Y247) polycrystalline bulks sintered under various conditions, 940–975 °C and P(O2) = 4–16 atm. Tc of oxygen annealed Y247 samples at 400 °C varied largely depending on the sintering conditions from ~60 to ~90 K. Samples sintered under higher P(O2) exhibited lower Tc, whereas they were confirmed to be of Y247 single phase by powder X-ray analyses. Strong relationship between orthorhombicity defined as 1000(b ? a)/(a + b) and Tc was found in Y247 as in the cases of REBa2Cu3O7?δ with light rare-earth elements, such as La, Nd, Sm, Eu and Gd. In addition, Tc‘s of samples with nominal compositions of Y2+xBa4?xO7O15?δ systematically decreased with an increase of x. These results indicated that partial substitution of Y for Ba occurred in the Y247 compounds possibly due to high occupancy ratio of oxygen at the Cu–O1-δ chain during the sintering process. 相似文献
9.
《Journal of magnetism and magnetic materials》1987,68(1):L1-L5
Two samples of Y1Ba2Cu3O9−δ, one fabricated at Los Alamos National Laboratory and the other at the University of Wuppertal, were tested in the rf field of a niobium cavity at 3 GHz and in a temperature range from 4.2 to 300 K. The data show a sharp reduction of the Joule losses in the samples beginning at an onset temperature of 98 and 92 K, respectively. The residual losses of the sample were measured at 4.2 K where the host cavity was superconducting. The ratio of these losses to the ones observed slightly above Tc was less than 1.1 × 10−2. This indicates that only a small fraction of the conduction electrons of the Y1Ba2Cu3O9-δ sample remain unpaired. The dependence of the rf losses on the rf magnetic field allows the determination of a maximum surface current density which is found to be about 5 × 104 A/cm2. 相似文献
10.
V. Bhat A. K. Ganguli K. S. Nanjundaswamy R. A. Mohan Ram J. Gopalakrishnan C. N. R. Rao 《Phase Transitions》2013,86(1-2):87-95
Abstract High-TC superconducting oxides of nominal La1.85Ba0.15 CuO4 and YBa2 Cu3 O7 have been prepared by using nitrate, carbonate, oxalate/malonate and citrate precursors. While the samples in the Y-system are generally monophasic YBa2Cu3O7?δ with TC around 90K, the preparations in the La-system are biphasic containing K2NiF4-like La1.85Ba0.15 CuO4 (TC = 30K) and a perovskite-like phase with' a much higher TC (200–300K). Effect of Ca, Zr, Ce as well as S substitution in YBa2Cu3O7?δ has also been investigated 相似文献
11.
12.
《Physics letters. A》1988,127(5):297-299
We have investigated the microstructure and compositional distribution of the Y1Ba2Cu3O7−x superconductor with scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction. It has been found that the microregion compositions are far from the ideal composition. This is especially due to the yttrium content which is higher than the expected amount in the interfacial region between crystalline grains. 相似文献
13.
J. Karthikeyan K. P. Sreekumar N. Venkatramani M. B. Kurup D. S. Patil V. K. Rohatgi 《Applied Physics A: Materials Science & Processing》1989,48(5):489-492
A study on the effect of powder, spray and coating parameters on superconducting properties of plasma-sprayed Y1Ba2Cu3O7–x
coatings has been carried out. Optimised spray parameters to yield strong, adherent and dense coatings on many substrates including AISI 304 SS and alumina have been obtained. Coatings show superconductivity after oxygen annealing at 950°C for an hour. Coatings thinner than 100 m do not show zero resistivity down to 77 K due to weak links between granular superconductors. Coatings prepared with fine powder have superior superconducting properties, viz. higherT
c andJ
c values than coarse powder coatings. The choice of substrate material strongly affects theJ
c values. 相似文献
14.
P. Allenspach J. Mesot U. Staub M. Guillaume A. Furrer S. -I. Yoo M. J. Kramer R. W. McCallum H. Maletta H. Blank H. Mutka R. Osborn M. Arai Z. Bowden A. D. Taylor 《Zeitschrift für Physik B Condensed Matter》1994,95(3):301-310
Neutron diffraction, neutron spectroscopy and magnetization measurements have been employed to study the structural, electronic, and magnetic behavior of eleven compounds with the general formula Nd1+y
Ca
v
Ba2–y–v
Cu3O
x
(0y0.5; 0v0.25; 6x7). The structure turned out to react to oxygen reduction similar as other 123-compounds, yielding discontinuities close to the metal-insulator-transition and the well-known relations of bond lengths as a function ofT
c. The crystalline electric field (CEF) interaction, splitting the 10-fold degenerate ground-state J-multiplet of the Nd3+-ions into five doublet states, was investigated by neutron spectroscopy. The derived CEF parameters have been used to determine changes in the electronic surroundings of the Nd3+ ions. In addition, with the help of the CEF parameters the thermodynamic magnetic properties of these compounds were calculated which turn out to be in good agreement with the experimental data. 相似文献
15.
TIAN Nailiang 《Chinese Journal of Lasers》1999,8(4):372-376
Introduction TheinvestigationofdirectcrystallizationofYBa2Cu3O7superconductorbylaserirradiationYBaCuOmaterialofstoichiometrical123compositionisinterested.Thedirectlasersynthesisofhightemperaturesuperconductorhasspecificdominace[1].Itisthefinestru… 相似文献
16.
M. K. Aliev G. R. Alimov T. M. Muminov B. A. Olimov Kh. I. Turkmenov I. Kholbaev L. I. Leonyuk R. F. Rumi 《Physics of the Solid State》1999,41(1):11-14
Y1Ba2Cu3O7−x
single crystals are investigated near T
c
≈92 K in fields 0<H⩽9 kOe using a modified ESR spectrometer. The temperature modulation method is used for the first time, together with the
traditional magnetic modulation method, to detect microwave responses in single crystals. Superconducting-transition peaks
shifted relative to one another in temperature and differing in shape are observed in the temperature dependence of the corresponding
signals ∂R/∂H and ∂R/∂T (R — microwave absorption). The evolution of these peaks as a function of the field and the angle π between H and the c axis of the single crystal is traced. It is shown that the difference in the temperature dependences of the derivatives ∂R/∂H and ∂R/∂T is due to the broadening of the superconducting transition characteristic of HTSCs.
Fiz. Tverd. Tela (St. Petersburg) 41, 14–17 (January 1999) 相似文献
17.
K. Nagasao T. Masui S. Tajima 《Physica C: Superconductivity and its Applications》2008,468(15-20):1188-1191
Electronic anisotropy was studied for overdoped (Y, Ca)Ba2Cu3O7−δ with various doping levels (p). It was found that the pseudogap-like behavior in the resistivity disappear when p exceeds 0.17, independent of the oxygen deficiency. The anisotropy ratio γ estimated from upper critical fields showed a rapid decrease at around p = 0.18, approaching γ = 3 for p > 0.20. 相似文献
18.
Study of the effect of the substitution of O by F,S, and Cl on the superconductivity of Y1Ba2Cu3O7−δ
We have studied the superconducting transitions of Y1Ba2Cu3D
x
O7–x– samples where O has been replaced by D=F, S, or Cl andx=0.2-2. No single phase compounds were obtained forx>0.2. No dramatic increase inT
c
was registered. Generally the results can be interpreted as a dilution of the highT
c
1 2 3 phase by other phases as the dopant concentration increases, ultimately suppressingT
c
completely. Possibly there is an increase ofT
c
for an intermediate dopant range,x, in the Cl series. 相似文献
19.
Lincoln Brum de Leite Gusm?o Pinheiro Alcione Roberto Jurelo Francisco Carlos Serbena Pedro Rodrigues Carlos Eugênio Foerster Adilson Luiz Chinelatto 《Physica C: Superconductivity and its Applications》2010,470(11-12):465-469
The effect of Er substitution on the mechanical properties of ab- and a(b)c-planes of melt-textured YBa2Cu3O7?δ is reported in the present work. The non-oxygenated samples were characterized by scanning electron microscopy, X-ray diffraction and mechanical properties by instrumented indentation and conventional Vickers indentation whereas the superconducting properties were determined by resistivity measurements on oxygenated samples. The X-ray pattern and EDS analysis revealed the presence of Y-123, Y-211 and BaCeO3 phases. Er substitution up to 5 wt.% did not affect the superconducting properties. No difference in hardness was observed for the ab- and a(b)c-planes. Elastic modulus of the a(b)c-plane was 10% higher than of the ab-plane. Differences in indentation fracture toughness obtained by conventional Vickers indentation of the ab- and a(b)c-planes was observed. The addition of 5 wt.% of Er did not affect significantly the mechanical properties of melt-textured samples when compared with pure melt-textured YBa2Cu3O7?δ. 相似文献
20.
《Physica C: Superconductivity and its Applications》1999,311(3-4):239-245
The orthorhombic structure of Ba2Cu2.89O6−y (sp. gr. Pccm, a=13.065(15), b=20.654(21) and c=11.431(8) Å) contains two nonintersecting symmetrically equivalent sets of parallel CuO2-chains running along [110] and [1̄10] directions. Along the c-axis the Cu–O sheets are separated by identical layers of Ba-atoms. The Cu–O chains are distorted within the xy plane producing zigzag. Three of 14 positions of copper atoms were found to be partly vacant that caused the significant shifts of the neighbouring Ba atoms in the plane. The determined structure of Ba2Cu2.89O6−y is compared to that of the monoclinic Ba2Cu3O6 modification, of another infinite-chain compound Sr0.73CuO2, and to one of the substructures of ladder compounds (Sr,Ca)14Cu24O41+y. The superconductivity in Ba2Cu2.89O6−y is associated with the CuO2-chains consisting of CuO4-squares sharing edges. The attention is paid to the coincidence of the temperatures of the superconducting transitions in Ba2Cu2.89O6−y and in ladder compound with the temperature of the sharp magnetic transition in another infinite-chain compound Sr0.73CuO2. 相似文献