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1.
Compounds of the form (M1−xM′x)2CuO4−δ and related compounds where M and M′ are Y, various rare earths from La to Lu, and the alkaline earths Sr and Ba, have been investigated in connection with high temperature superconductivity. High temperature superconductivity is confirmed for the system (La1−xBax)2CuO4−δ, (La1−xSrx)2CuO4−δ and (Y1−xBax)2CuO4−δ with superconducting transition temperature Tc onsets of 30 K, 38 K and 90 K, respectively. We have found that the related systems (Eu1−xBax)2CuO4−δ and (Sm1−xBax)2CuO4−δ also exhibit high temperature superconductivity with Tc onsets of 95 K and 65 K, respectively. The highest Tc onset observed in this investigation was 97 K for a sample with the nominal composition of the spinel structure Y0.33Ba0.67Cu2O4−δ. Measurements of the specific heat C as a function of temperature T on a La0.8Sr0.2CuO4−δ sample reveal a break in slope in the C/T vs T curve at the Tc midpoint, but no clearly discernable jump in C at Tc. A linear term ≈ λ′T in C was observed at low temperature in the superconducting state.  相似文献   

2.
Superconductivity around 90K is observed in mixed and single phase system of LnBaCuO (Ln = Y, Ho, Er). Resistivity, X-ray powder diffraction and AC susceptibility measurements were carried out on samples of the mixed phase systems Ln2−xBaxCuO4−y (Ln = Ho, Er), Y1.2Ba0.8Cu1+xO4+x−y(0<x<5) and single phase system Ba2LnCu3O7 (Ln = Y, Ho, Er). Ln2−xBaxCuO4−y consists of Ba2LnCu3O7, BaCuLn2O5, Cu2Ln2O5 and starting materials and shows a small diamagnetic signal below Tc in the temperature dependent AC susceptibility. Y1.2Ba0.8Cu1+xO4+x−y is a mixture of Ba2YCu3O7, BaCuY2O5 and CuO and also indicates a small diamagnetic signal at 92K. Interesting resistivity anomalies occur in the Y1.2Ba0.8Cu4O7−y and Ho0.8Ba1.2CuO4−y composites including large drops in the resistivity at ∼220 and ∼120K, respectively. The pure compounds, Ba2LnCu3O7 (Ln = Y, Ho, Er) show sharp resistive superconducting transitions and bulk Meissner effects of 90%.  相似文献   

3.
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   

4.
本文报道了对PrxY1-xBa2Cu3O7-δ体系超导体红外光谱研究的结果。发现在整个光谱范围内(中红外和远红外),Pr含量增加的直接结果是大部分反射峰的强度增强。在远红外区,Y原子的“指纹”性声子190cm-1峰的频率位置与Pr含量无关,证明了Pr在该体系中价态要比Y的+3价高,介于+3价与+4价之间。通过对各个声子结构的指认,我们发现:随Pr含量增高,声子活性增强的振动模必定是属于CuO2面内的或与CuO2平面平行的振动模,与YBa2Cu3O7-δ体系中减少氧的情况类似。这意味着CuO2面内的振动对于高温超导性的重要作用。 关键词:  相似文献   

5.
《Journal of luminescence》1987,37(3):117-121
Lanthanide fluorescence has been observed for the first time in the high temperature superconductors that have been recently discovered. Laser excited fluorescence and fluorescence excitation spectra of La1.85-xRExSr0.15CuO4 for RE=Pr and Eu and x=0.02, 0.18, 0.36 and 1.85 are presented. There is substantial inhomogeneous broadening caused by the Sr2+ in the materials containing a single rare earth and additional broadening caused by the ionic size mismatch in the materials with two rare earths. The samples have 3 crystallographic sites for the lanthanide ion. No fluorescence was observed for the higher temperature superconductors, Y1Ba2Cu3O9-δ, doped with 10 and 100% Eu3+.  相似文献   

6.
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   

7.
《Physics letters. A》1987,123(1):31-33
We present the results of a study of the crystalline structure of the high-temperature superconducting (above 110K) phase in the single-phase ceramic compounds YBaCuO. We have concluded that the crystal symmetry of this HTS phase with chemical composition Y1.2Ba0.8CuO4−δ is orthorhombic type with crystallographic lattice constants a=0.3815 nm, b=0.3457 nm, c=2.650 nm.  相似文献   

8.
Abstract

We present here the results of our resistive investigations of a sample of the Y-Ba-Cu-O system which strongly suggest the possibility of superconductivity at 140K. The composition of this sample is Y0.7Ba0.3CuO2,3?δ which is different from that of the single phase system YBa2Cu3O6+x.  相似文献   

9.
205Tl-NMR in Tl2Ba2Can-1CunO8?δ for differentn and δ is reviewed. Forn=2,3 the205Tl spectra consist of two lines. The main line arises from Tl(1) in the TlO-layer whereas the defect line belongs to Tl(2) in the Ca-layers between the CuO2-layers. The temperature dependent Knight shift of the Tl(2) (defect) line is caused by the hyperfine interaction with the CuO2-layer and is strongly related to the oxygen content of the sample. We find quasipartticle behavior for the T1(2) line similar to the89Y Knight shift in the YBa2Cu3O6+δ system. In contrast the T1(1) line shows strong antiferromagnetic correlations with indication of pseudo spin gap opening above the superconducting transition temperatureT c.  相似文献   

10.
The magnetic ordering of Er ions in Er2Ba4Cu7O15-δ (δ = 0:7 and δ = 0:08) has been studied by low temperature heat capacity measurements. The Néel temperature T N of Er2Ba4Cu7O15-δ is almost independent of the oxygen concentration (TN = 0:54K for δ = 0:08 and T N = 0:50K for δ = 0:7). While an anisotropic two-dimensional (2D) Ising model describes the experimental data very well for Er2Ba4Cu7O14:92, this model cannot be applied to the oxygen reduced sample Er2Ba4Cu7O14:3. By using a model consisting of 1D-Ising chains and of 2D-Ising clusters of Er3+ ions we could fit the specific heat data of Er2Ba4Cu7O14:3 accurately. Our measurements show clearly that with the reduction of the oxygen content the in-plane anisotropy of the magnetic exchange coupling increases.  相似文献   

11.
测量了温度范围为4.2—300K的Y1-xPrxBa2Cu3O7+δ(x=0,0.1,0.2,0.4,0.5,0.61.0)的红外反射谱,发现在低温下Ba模有双模行为,随着x值增大双模强度反转,在YBa2Cu3O7+δ中已被判定为Y模的位于194cm-1的反射峰的位置与Pr的含量无关,即用Pr部份或全部替代Y时此峰不发生频移。建议Pr在Y1-xPrxBa2Cu3O7+δ,中是正4价,Pr的替代使原来可移动的空穴被定域在Pr的周围,使超导电性受到压制。 关键词:  相似文献   

12.
We have investigated various compositions of Ba-Y-Cu-O, resulting in the preparation of single phase 90 K superconducting material of composition (Ba0.67Y0.33)CuO3−δ and the identification of the structure of this superconducting phase by lattice imaging as a layered perovskite. The single phase material had a resistive transition with a midpoint at 92 K and a 1.3 K width (10%–90%) as well as a sharp low-field (H = 0.01 Oe) susceptibility transition.  相似文献   

13.
The Y0:4Pr0:6Ba2-xSrxCu3O7-δ (x = 0;1:0) samples were prepared and the structural properties were studied by X-ray Rietveld analysis. It has been found that the average Pr-O bond length increases from 2.435Å at x = 0 to 2.457Å at x = 1:0, the Cu(2)-O-Cu(2) angles within the CuO2 planes become larger, and there is no significant mutual substitution between Pr and Sr ions. The BVS calculation suggests that Sr doping brings about the increase of the hole concentration on CuO2 planes and the weakening of Pr-O covalent mixing. Our work supports that Pr-O covalent mixing effect is responsible for the superconductivity suppression by Pr.  相似文献   

14.
We have studied the magnetic phase diagram for the bilayer compound Y1-x Cax Ba2 Cu3 O6 in the regime of low doping (hole concentration within a CuO2 plane, psh < 0.1). For psh < 0.03, the data demonstrate the freezing of the spin degrees of freedom associated with the doped holes into a spin‐glass‐like state which is superimposed on the preexisting long range order of the Cu2+ spins. Only a single spin‐glass like transition at a temperature Tg is observed for samples in the hole concentration range 0.03 < psh < 0.1. While the threshold for the occurrence of superconductivity is almost the same (psh > 0.06) for the Y1-x Cax Ba2 Cu3 O6 and the La2-x Srx CuO4 systems, the magnetic correlations that coexist with superconductivity are considerably stronger in the bilayer Y1-x Cax Ba2 Cu3 O6 system as indicated by significantly increased transition temperatures Tg. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

15.
Y1?xHoxBa2Cu3O7?δ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) thin films were prepared on LaAlO3 (0 0 1) substrates by trifluoroacetate metal organic deposition (TFA-MOD) without change of the processing parameters. The highest Jc was attributed to the sample of Y0.6Ho0.4Ba2Cu3O7?δ thin film, whose critical current density is about 1.6 times as compared to that of YBa2Cu3O7?δ thin film at 77 K and self field. The flux pinning type was not varied with Ho substitution and can be attributed to δl pinning model, which is attributed to the close ionic radius between the Y3+ and Ho3+ ions. The improvement of Jc by Ho substitution without change of the processing parameters will provide an effective route to enhance the Jc of YBCO-based thin films using TFA-MOD method.  相似文献   

16.
本文报道,通过对Y1-xCaxBa2Cu3-xMxO7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa2Cu3-xMxO7-δ(M=Fe,Ni)体系进行比较,发现Y1-xCaxBa2Cu3-xFexO7-δ体系的Tc显著地高于相应x值的YBa2Cu3-xFexO7-δ体系,而Y1-xCaxBa2Cu3-xNixO7-δ体系则相反,Tc低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(nH)变化相互补偿,抑制了仅Fe替代时引起的nH和Tc急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y1-xCaxBa2Cu3-xFexO7-δ体系属于CuO2平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y1-xCaxBa2Cu3-xNixO7-δ体系,由于Ni2+离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni2+离子的拆对效应是引起Tc下降的直接原因。 关键词:  相似文献   

17.
The influence of nonstoichiometric disorder on the in-plane resistivity and SC-transition has been investigated for Nd2−xCexCuO4+δ single crystal films (x=0.15 and 0.18). It is shown that with increasing of δ the in-plane normal state resistivity increases (the mean free path diminishes) and SC-transition temperature decreases with essential broadening of the transition region. The observed evolution from homogeneous metallic (and superconducting) Nd2−xCexCuO4+δ system to inhomogeneous dielectric one is described as Anderson-type disorder-induced transition in a two-dimensional electron system.  相似文献   

18.
《Physics letters. A》1987,126(2):130-132
The superconducting transition temperature Tc, detected by the Meissner effect, of the single-phase (Y1.2Ba0.8)4Cu4 O16−δ ceramic compound has been studied under hydrostatic pressure up to 3.4 kbar. The Tc increases with the increase of pressure at a rate of 1.5 K/kbar. The observed pressure behaviour of Tc is discussed with reference to a crystal structure and a cooperative bipolaron tunneling induced by Jahn-Teller distortions.  相似文献   

19.
Ba2CuO3/HgBa2CuO4+δ and Mn3O4/Mn2O3 couples were employed to control the mercury and oxygen partial pressures, respectively, during the synthesis of chromium doped Hg-1201 phase in the sealed quartz tube. Suitably adjusted conditions allowed us to prepare series of single phase samples of the final composition Hg0.7Cr0.2Ba2CuO4+δ determined by weight changes and EMA. The oxygen stoichiometry was modified by the oxygen partial pressure in the range of pO2=0.05–1.59 atm. The X-ray diffraction and magnetic susceptibility study revealed linear dependence of the structural parameters and parabolic one of Tc vs. log pO2. Multiphase samples, however, form for too high oxygen activity, namely for pO2=5.16 atm.  相似文献   

20.
A complete solid solution range exists between the systems YBa2Cu3O7−δ and (Pb,Cu)Sr2(Ca,Y)Cu2O7−δ has been found with general stoichiometry (Pb0.75xCu1−0.75x)(Sr2xBa2−2x)(Ca0.5xY1−0.5x)Cu2O7−δ. Energy dispersive spectrometry and X-ray diffraction identified that a true solid solution exists. Superlattice structures observed by electron diffraction across the solid solution range have a modulation range have a modulation periods along a* which can be varied by altering both the compositional parameter x and the overall oxygen content. The existence of these superlattices infers that the solid solution is non-random and therefore thermodynamically non-ideal. The superconducting transition temperatures, Tc, across the solid solution range are also strongly dependent on the composition, x, but no direct relationship with the modulation period has been established. From these studies it may be concluded that the solid solution between known superconductors is possible, although involving some partial ordering of the lattice, but ordering of cations in the rock-salt to charge reservoir layer is not a significant factor in determining the superconducting properities, which depend more closely on the overall composition and hence on the ability of the charge reservoir layer to transfer charge to the superconducting layers.  相似文献   

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