共查询到20条相似文献,搜索用时 15 毫秒
1.
W. H. Fietz R. Quenzel H. A. Ludwig K. Grube S. I. Schlachter F. W. Hornung T. Wolf A. Erb M. Klser G. Müller-Vogt 《Physica C: Superconductivity and its Applications》1996,270(3-4):258-266
The pressure effect on Tc of polycrystalline and single crystalline YBa2Cu3Ox investigated as a function of oxygen content x by ac-susceptibility measurements under helium pressure. In the overdoped region x> 6.93 the single crystals show a negative dTc/d p, as expected from the charge transfer model. For optimally doped samples with x = 6.93 we find dTc/d P = 0.4 K/GPa which points to pressure effects on Tc aside from charge transfer. In the underdoped region x < 6.93 the dTc/d p values obtained from the experiment depend strongly on the storage temperature of the sample during the experiment. When the samples are stored at temperatures well below 240 K throughout the entire experiment including pressure application and pressure release, dTc/d p increases to approx. 7 K/GPa at x = 6.7 but with a further decrease of the oxygen content the dTc/d p drops to approx. 2 K/GPa at x = 6.4. These effects are intrinsic to the YBa2Cu3Ox structure and can be explained by considering the anisotropic structure of YBa2Cu3Ox. The decrease of the c-axis lattice parameter results in a charge transfer to the CuO2-planes mainly [1], whereas the compression of the a- and b-axis lattice parameter is known to produce different pressure effects which are responsible for the peak in dTc/d p at x = 6.7 [2]. When pressure is changed at room temperature oxygen ordering effects occur which cause a relaxation of Tc to the equilibrium value Tc(p) at this pressure with a time constant depending on the oxygen content x. A decrease x results in a peak effect in dTc/d p at x = 6.7 again, which is enhanced to approx. 12 K/GPa. If the oxygen content is decreased further, dTc/d p first drops to 5 K/GPa at x = 6.6, but the increases to values of more than 20 K/GPa for x < 6.42. These giant pressure effects at low oxygen contents are mainly caused by a reversible Tc increase (dTc/d p)O due to pressure induced oxygen ordering via oxygen motion between unit cells. 相似文献
2.
H. J. H. Smilde H. Hilgenkamp G. J. Gerritsma D. H. A. Blank H. Rogalla 《Physica C: Superconductivity and its Applications》2001,350(3-4):269-275
All-thin-film ramp type Josephson junctions between YBa2Cu3O7−δ and Nb have been fabricated. This procedure allows connections between high-Tc and low-Tc superconductors at different crystal sides of the high-Tc superconductor on one chip, which is of great interest for novel phase devices. A thin Au layer is incorporated as a chemical barrier to avoid oxygen transfer from the YBa2Cu3O7−δ to the Nb. Critical current densities up to 600 A/cm2 are obtained at T=4.2 K, with typical RnA values of 0.8 μΩ cm2. The variation of the magnetic field dependence of the critical current with the angle between the junction barrier and the YBa2Cu3O7−δ crystal axes is explained by considering a predominant dx2−y2 order parameter symmetry of the YBa2Cu3O7−δ. The successful fabrication of these junctions allows the implementation of novel superconducting electronics, such as complementary Josephson circuitry or proposed qubit concepts, using the unconventional order parameter symmetry of the high-Tc superconductor. 相似文献
3.
Hye-Soo Shin In-Sang Yang W. -C. Lee 《Physica C: Superconductivity and its Applications》1995,250(3-4):275-281
Single crystals with known Tc values of Y1−xPrxBa2Cu3O7−δ (Y---Pr1:2:3) and YBa2Cu3−xZn3−xZnxO7−δ (Y---Zn1:2:3) systems are studied by Raman measurements. The Raman spectra for (Y---Pr1:2:3) single crystals show that the frequencies of Ba and Oz modes increase as the Pr content increases. The results are consistent with the hole-localization scheme proposed for the suppression of superconductivity in the polycrystalline Y---Pr1:2:3 systems. On the other hand, in the Y---Zn1:2:3 system, all the Raman modes do not change in frequencies. However, the FWHM of the Cu(2) mode increases with the decrease of Tc, indicating strong scattering of charge carriers by the substituted Zn ions in the CuO2 planes. The induced disorder in the CuO2 planes may be related with suppression of Tc in the Y---Zn1:2:3 system. Thus, the suppression mechanism in the Y---Zn1:2:3 systems seems to be different from that in the Y---Pr1:2:3 systems. 相似文献
4.
H. Wu M. J. Kramer K. W. Dennis R. W. McCallum 《Physica C: Superconductivity and its Applications》1997,290(3-4):252-264
The lower solubility limits of Nd1+xBa2−xCu3O7 (Nd123ss) in 1 bar, 0.2 bar, 0.01 bar, and 0.001 bar oxygen partial pressure (PO2) were studed by differential thermal analysis (DTA) and X-ray diffraction (XRD). Large relative changes in stability with decreasing PO2 explain why sharp superconducting transitions can be achieved in PO2 ≤ 0.01 bar while processing in 0.2 to 1 bar PO2 tends to produce broad transitions. While the lower solubility limits in 0.01 bar and 0.001 bar PO2 remain at x = 0.00, the solubility limits in 0.2 bar and 1 bar PO2 show a narrowing with decreasing temperature. Because of the narrowing of the solubility range in 1 bar PO2, oxygen annealing of Nd123 initially processed in low PO2 will result in precipitation of second phases which act as flux pinning centers. 相似文献
5.
R. Kita S. Kawamoto K. Ohata H. Izumi R. Itti T. Morishita S. Tanaka 《Physica C: Superconductivity and its Applications》1990,170(5-6):500-504
Ca-doped YBa2Cu4O8 (124) thin films are prepared on (100) SrTiO3 substrates by annealing the amorphous films deposited using a pulsed laser deposition technique. The X-ray diffraction measurements show that the Ca-doped YBa2Cu4O8 phase is formed by annealing below 800°C at a oxygen pressure of 1 atm. The 124 films have c-axis orientation normal to the substrates. As the Ca content increases, the proportion of the 123 impurity phase in the samples increases. The onset temperature of superconductivity of the Y(Ca)Ba2Cu4O8 films increases from 79 K to 88 K with an increase Ca-substitution for 5 to 10% of Y. 相似文献
6.
Superconducting transition temperature (Tc), Ca content and oxygen deficiency are studied on GaSr1.8Ca0.2Yb1−xCaxCu2O7 (x≤0.35). Superconducting samples with Tc=52 K are prepared after the annealing at 20 MPa of oxygen. The Tc is reduced through a slight oxygen loss accompanied by annealing in air above 650°C. The oxygen loss suggests the presence of short Cu–O chains in the GaO4 slab. The formal valence of planar Cu required for the appearance of superconductivity depends on oxygen and Ca contents. The critical formal Cu valences are 2.105 and 2.125 for the samples annealed in air at 600°C and at 835°C, respectively. The values are higher than those of usual high-Tc superconductors. This can be explained by a high concentration of localized holes in the CuO5 slab. 相似文献
7.
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
8.
H. R. Kerchner Yang Ren Sun J. R. Thompson H. R. Khan J. O. Thomson D. K. Christen 《Physica C: Superconductivity and its Applications》1995,250(3-4):331-339
Superconductivity in polycrystalline YBa2AlxCu(3−x)O7−δ materials was characterized by dynamic AC and quasistatic DC magnetometry. Intragranular persistent current density and low-loss intergranular critical current density were deduced using DC and AC techniques, respectively. Addition of aluminum produced modest increases in the intragranular persistent current for x < 0.2, but drastically reduced the intergranular critical current density for x = 0.2. The critical temperature Tc for superconductivity decreased only 4% for Al content up to x = 0.2. 相似文献
9.
Hiromi Takahashi Hirohiko Izumi Katsumi Ohata Takashi Hase Masato Sasaki Tadataka Morishita Shoji Tanaka 《Physica C: Superconductivity and its Applications》1992,190(4):427-432
The crystal structure of YBa2Cu3O7−x thin films has been investigated by cross-section transmission electron microscopy. The samples were deposited on MgO (100) substrates at 670°C with substrate bias voltages of ±300 V. For the unbiased case, c-axis, a-axis and (103) oriented domains normal to the substrate surface were observed. In this film, the c-axis oriented domains are dominant, but the crystal often exhibits a longer c-lattice constant than that of the YBa2Cu3O7−x system, so extra cationic layers are inserted in the YBa2Cu3O7−x intrinsic stacking sequence. For the case of −300 V, rotated domains were dominant in the entire film; however, c-axis oriented domains also grow from the substrate surface. Small-angle semicoherent grain boundaries between them were observed. In the case of +300 V, all the grains show c-axis oriented YBa2Cu3O7−x. The degree of preferential orientation of the grains is reduced at negative bias voltage of −300 V and the structure defects are reduced by applying a positive bias of +300 V. 相似文献
10.
Intercalation thermodynamics and chemical diffusion of oxygen in the solid solution YBa2Cu3−xCoxO6+δ
E. B. Mitberg M. V. Patrakeev A. A. Lakhtin I. A. Leonidov V. L. Kozhevnikov K. R. Poeppelmeier 《Solid State Ionics》1999,120(1-4):239-249
The equilibrium oxygen content as a function of the temperature and oxygen pressure was measured for the solid solution YBa2Cu3−xCoxO6+δ, where x=0, 0.2, 0.4, 0.6, 0.8, by using coulometric titration in the temperature range 600–850°C and oxygen pressures between 10−5 and 1.0 atm. The change in the partial molar enthalpy and entropy of the intercalated oxygen was determined at different oxygen and cobalt contents. The oxygen chemical diffusion was studied by thermogravimetric relaxation in the oxygen-controlled atmosphere. The thermodynamic data were employed to determine how the chemical diffusion coefficient, the thermodynamic factor and the random-diffusion coefficient depend on oxygen content in specimens with different cobalt concentration. The oxygen intercalation thermodynamics and diffusivity results provide evidence of ordering phenomena on a microscopic scale in the basal plane of the tetragonal solid solution YBa2Cu3−xCoxO6+δ. A model for the oxygen diffusion is suggested to explain the large difference between the random and tracer diffusion coefficients in YBa2Cu3O6+δ 相似文献
11.
Z. Tomkowicz 《Physica C: Superconductivity and its Applications》1999,320(3-4):173-182
Pr concentration dependence of the superconducting transition temperature Tc in the Ho1−xPrxBa2Cu3O7−δ system is determined from measurements of DC electrical resistance. This dependence coincides with that for the parallely studied Y1−xPrxBa2Cu3O7−δ reference system. Both systems have the same value of the critical concentration xc=0.58, in accordance with nearly equal ionic radii of Ho3+ and Y3+ ions. It has been shown that the Tc(x) curve can be described with a single mechanism based on a decreasing number of sheet holes trapped by PrIV-ions, if one takes also into account that the number of these ions changes with x. 相似文献
12.
H. Weyten G. Fransen R. Kemps A. Buekenhoudt J. Cornelis 《Physica C: Superconductivity and its Applications》1996,270(3-4):207-215
High-Tc superconducting thin films have been deposited in situ by means of a plasma assisted metal-organic chemical vapour deposition (PAMOCVD) process on LaAlO3. An EMCORE high-speed rotating disc reactor was used to deposit the films at a substrate temperature of 600°C to 800°C. The system is equipped with a (remote) 120 W microwave plasma generator. The oxidising plasma gas is N2O and/or O2 while Ar was used as the inert carrier gas for the different metal-organics. The influence of different process parameters (such as the temperatures of the metal-organics, substrate temperature, and plasma gas composition) on the superconductive properties and on the morphology of the films was investigated. Surface morphology and composition were studied by SEM/EDX or EPMA, and AC susceptibility measurements were used to investigate the superconductive properties (Tc and Jc). X-ray diffraction measurements indicated that single-phase YBa2Cu3O7−x films were epitaxially grown with the 00l orientation perpendicular to the substrate surface. The critical temperature (Tc) of the films is about 90 K and the critical current density (Jc) is higher than 106 A/cm2 at 77 K and zero field. 相似文献
13.
The phase equilibria around YBa2Cu3O7−x (123) and YBa2Cu4O8 (124) phases at low oxygen partial pressure (1 atm) were investigated by X-ray diffraction and thermal analysis. The coexistence of 123 and 124 phase was confirmed under 1 atm oxygen pressure. By using the high temperature X-ray diffraction method, the univariant reaction YBa2Cu3O7−x+Cu2OY2BaCu2O2+O2 was identified. The oxygen partial pressure dependence of several univariant reactions has been investigated and the existence of two invariant reactions of L+O2YBa2Cu3O7−x+ BaCuO2+CuO+Cu2O and L+Y2BaCuO5+O2YBa2Cu3O7−x+CuO+Cu2O was deduced to occur at 1103 K under 0.0032 atm O2 and at 1143 K under 0.0085 atm O2, respectively. 相似文献
14.
K. Nishi Y. Hatsukade S. Tanaka K. Awazu H. Horiike 《Infrared Physics & Technology》2008,51(5):463-467
Since the discovery of high-temperature cuprate superconductors, there has been much intensive study about the mechanism of them. However, identifying the dynamical mechanism behind them remains one of the great challenges in condensed matter physics. We investigated the high-temperature YBa2Cu3O7−x superconducting films by using a free electron laser (FEL). The method is a type of photoelectron spectroscopy called a free electron laser internal photoemission. The spectrum of the photocurrent induced by FEL was measured in the case of 15 K and 100 K. We estimated the superconductive gap energy of YBa2Cu3O7−x by comparing the photocurrent spectrum of the superconductive state with that of non-superconductive state. 相似文献
15.
Evidence is presented that in high-Tc superconductors the electrostatic interaction as expressed by the Madelung energy is the key factor in determining the charge distribution and in particular the distribution of the holes between the CuO2-planes and other structural subunits. Specifically, this explains the phase diagram (Tc as a function of oxygen content and oxidizing power) of cation-substituted YBa2Cu3O6+y and the oxygen ordering in YBa2Cu3O6.5. Moreover, we argue that the dependence of Tc on strontium content in La2−xSrxCuO4 is similarly due to the fact that holes go into the (La,Sr)O-sheets as well as into the CuO2-planes. 相似文献
16.
J. G. Noudem E. S. Reddy G. J. Schmitz 《Physica C: Superconductivity and its Applications》2003,390(4):286-290
The recently reported superconducting YBa2Cu3Oy (Y123) foams are highly interesting and promising for variety of applications. In this report we present first magneto-transport measurements of the superconducting properties of these foams. The investigations reveal the superconducting properties being similar to those of bulk melt processed materials. The 123 foams reveal a Tc of 92 K and have a magnetization Jc of 40,000 A/cm2 at 77 K and 0 T. The measurements of magnetic hysteresis versus field show a high anisotropy of the critical current density up to Jcab/Jcc7. 相似文献
17.
J. Baak S.I. Mukhin H.B. Brom M.J.V. Menken A.A. Menovsky 《Physica C: Superconductivity and its Applications》1993,210(3-4):391-400
Specific heat data below 1 K of Bi2Sr2CaCu2O8 and YBa2Cu3O7 are analyzed. For YBa2Cu3O7 the nuclear specific heat, CN, amounts to 38T−2 μJ/mol K. CN for Bi2Sr2CaCu2O8 exceeds that of YBa2Cu3O7 by a factor of 15. The nuclear quadrupolar specific heat contribution alone is insufficient to explain the data for YBa2Cu3O7, while lack of NQR data does not allow such a comparison in Bi2Sr2CaCu2O8 to be made. The contribution to CN from nuclear spins coupled via the contact hyperfine interaction with correlated magnetic spins (in the CuO2 plane) is derived as a function of the correlation length. This contribution can be treated independently from the quadrupolar term. We show that the excess specific heat in YBa2Cu3O7 likely originates in a few percentage of an impurity (oxygen deficient) phase with a strong hyperfine field on the Cu nuclei. 相似文献
18.
Masahito Ban Katsumi Suzuki Youichi Enomoto 《Physica C: Superconductivity and its Applications》1997,290(3-4):345-353
SiO2 film coated as a passivation layer for YBa2Cu3O7−x (YBCO)-based microwave devices is investigated by measuring the microwave characteristics of microstrip line resonators. The SiO2 film is deposited with its 0.3 to 0.4 μm thickness by a sputtering method using Ar + 30%O2 plasma. These deposition conditions do not degrade the microwave characteristics and the critical temperature (Tc). Next, the SiO2 film coated resonators are compared with the uncoated ones for two kinds of degradation conditions: a 200°C annealing in air, and an exposure to air at 85°C and 85% RH (relative humidity). We find that the SiO2 passivation film prevents the YBCO thin film from the surface degradation and reacting with water. 相似文献
19.
Temperature dependence of the critical current in YBa2Cu3O7−δ and Bi2Sr2Ca1Cu2O8 Josephson junctions
B. A. Aminov N. B. Brandt Nguyen Min Thuy Ya. G. Ponomarev M. V. Sudakova
A. R. Kaul
I. E. Graboi Yu. D. TretiakovJ. Wittig
S. P. Kobeleva
L. M. FisherL. Rosta
《Physica C: Superconductivity and its Applications》1989,160(5-6):505-510We have studied the stationary Josephson effect on YBa2Cu3O7−δ (Tc=90 K) and Bi2Sr2Ca1Cu2 O8 (Tc=80 K and 87 K for two samples of different origin) ceramic based junctions. The temperature dependence of the critical current near Tc has been found as Ic≈(Tc-T)
for the Y-Ba-Cu-O samples indicating that they should be classified as S-N-I-N-S type junctions. The I-V curves of the Bi-Sr-Ca-Cu samples show the typical behaviour of S-I-S structures. Using Ambegaokar-Baratoff's theory for Bi2Sr2Ca1Cu2O8, the temperature dependence of the superconducting state gap Δ(T) was calculated and it was evaluated that 1.452Δ(0)/kBTc3.5. 相似文献
20.
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