Anisotropy of the superconducting critical magnetic field HC2 of LaMCuO system(M = Sr and Ba)

Preliminary measurement of the superconducting critical magnetic field H_c2 of LaMCuO system (M = Sr and Ba) with layered perovskite structure has been carried out. The results show a quite large anisotropy of H_c2 indicating that the present system has a two dimensional character of the electron transport. The measured conductivities seem to be consistent with the values estimated from the observed H_c2 by use of an ideal two dimensional band with free electron mass.     

Superconductivity in the LnBaCuO system (Ln = Y,Ho, Er)

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 Ln_2−xBa_xCuO_4−y (Ln = Ho, Er), Y_1.2Ba_0.8Cu_1+xO_4+x−y(0<x<5) and single phase system Ba₂LnCu₃O₇ (Ln = Y, Ho, Er). Ln_2−xBa_xCuO_4−y consists of Ba₂LnCu₃O₇, BaCuLn₂O₅, Cu₂Ln₂O₅ and starting materials and shows a small diamagnetic signal below T_c in the temperature dependent AC susceptibility. Y_1.2Ba_0.8Cu_1+xO_4+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 Y_1.2Ba_0.8Cu₄O_7−y and Ho_0.8Ba_1.2CuO_4−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%.     

High Tc superconductivity of a TlBaCaCuO compound

A TlBaCaCuO_4.5+x compound has been investigated from the point of view of superconductivity. Depending on the heat treatment, one part of the samples exhibits superconductivity with an onset of 121 K and a zero resistivity of 106 K, while the other part of them shows only a sharp drop in resistivity at 130 K which hints at the existence of superconducting domains. This picture was confirmed by magnetic and ESR measurements giving possibility for estimation of the critical magnetic fields.     

Superconductivity and processing of single Bi−O layered cuprates in the (Bi,Pb)−Sr−(Ca,Y)−Cu−O system

The effects of improved materials processing on single Bi–O layered cuprates in the (Bi, Pb)–Sr–(Ca, Y)–Cu–O system have been investigatged. For Bi-1212 we have improvedT _c to 102 K. The bulk nature of superconductivity is confirmed by the presence of superconducting volume fractions ( ZFC) around 30–40%. The critical current density is 2×10⁶ Acm^–2 at 5 K and 0 T. Moreover, indications for the presence of a second phase probably Bi-1223 with a transition to superconductivity in the range of 115–150 K have been found.     

Zero resistance above 90K in superconducting oxides ErBaCuO and YbBaCuO

Superconductivity transition has been observed by electrical resistance and a.c. magnetic susceptibility measurements in ErBaCuO and YbBaCuO systems. The highest T_c(ϱ=0) is 90.3K for ErBaCuO and 91K for YbBaCuO.     

Superconductivity in the (La,Ln)2−x(Ba,Sr)xCuO4 system

Abstract

Several (La_1?y Ln_y)_2?x Sr_x(Ba_x)CuO₄ systems show superconductivity in the 15–40K region. Marginal metallicity of the non-superconducting phases and the role of the nominal Cu³+ /Cu ²⁺ ratio are discussed. Possible importance of hole-hole coupling (forming resonating O-O bonds) is indicated.     

Superconductivity of Y–Ba–Cu–O and substituted systems

Superconductivity of Y-Ba-Cu-O system is studied in the composition 2:2:3 and 1:2:3 of Y:Ba:Cu. The effect of replacement of Y or Ba by divalent Sr and Ca, trivalent Ce and tetravalent Zr is studied. X-ray diffraction, SEM and TEM techniques are used for materials characterization. Superconducting transition temperatures are measured resistively. Rapid resistance drop observed above 230 K in Y-Ba-Sr-Cu-O and Y-Ba-Ca-Cu-O systems indicate the possible existence of superconductivity above 230 K. Substitution of Ce in place of Y is found to reduce the onset Tc from 95 K to 80 K. For the first time, replacement of Cu by Zr in Y-Ba-Cu-O has yielded the onset Tc of about 105 K.     

Superconductivity of Bi1.6Pb0.4Sr2Ca3Cu4O12

The superconducting ceramics Bi1.6Pb0.4Sr2Ca3Cu4O12 have been prepared by the melt-casting method.A zero resistance temperature at 60K has been observed.It has been found that the superconducting phase temperature Tc increases with increasing sintering temperature,The effect of Pb content on the superconductivity of the ceramic has been studied.The microstructure of the Sample has been investigated by scanning electron microscopy.Phase analysis has been carried out by x-ray diffraction patterns and energy dispersive analysis through x-ray spectroscopy.     

Electron diffraction and electron microscopic study of BaYCuO superconducting materials

Electron microscopy and electron diffraction have been applied to show that the orthorhombic phase in the compound Ba₂YCu₃O_7−δ is responsible for the high superconducting transition temperature. A positive correlation is found between the volume fration of the orthorhombic phase and the superconducting transition temperature. By means of an “in-situ” heating experiment it is found that the orthorhombic phase is formed on cooling from a high temperature tetragonal phase with disordered vacancies. It is suggested that the low temperature tetragonal phase that occurs in the same specimens as the orthorhombic phase also contains an ordered arrangement of vacancies different from that present in the orthorhombic phase. The order-disorder transition associated with the structural vacancies is shown to be reversible, provided there has been no oxygen loss.     

The superconductivity,structure and microstructure of BaYScCu oxides

We added small amount of Sc (0.05–0.35at.%) to BaYCu oxide and found that the superconductivity deteriorated drastically when the Sc content reached 0.325at.%. X-ray and electron diffraction showed that the orthorhombic perovskite structure changed to multi-phase structure with unidentified phases. The microstructures observed by TEM are of needle like morphology. Their phases are not yet identified.     

Tunneling and point-contact spectroscopy of high-T c superconductors M−Ba2Cu3O7 (M=Y,La, Eu)

Tunneling and point-contact measurements have been performed on different high-T _c superconductors M–Ba₂Cu₃O₇ with M=Y, La, Eu. The average energy gaps deduced from the tunneling spectra are about 2=33 meV for the Y- and La-type samples and about 2=38 meV for the Eu-type samples, which give ratios 2/k _B T _c in the range from 4 to 6. The point-contact characteristics show a distinct minimum in the differential resistance about zero bias and additional sharp spikes up to 40 mV. From these pointcontacts we can give an estimate of the critical current, yielding values in the range from 0.2 to 3 mA.     

Superconductivity of the Sr2Ca12Cu24O41 spin-ladder system: are the superconducting pairing and the spin-gap formation of the same origin?

Pressure-induced superconductivity in a spin-ladder cuprate Sr2Ca12Cu24O41 has not been studied on a microscopic level thus far although the superconductivity was already discovered in 1996. We have improved the high-pressure technique using a large high-quality crystal, and succeeded in studying the superconductivity using 63Cu nuclear magnetic resonance. We found that the anomalous metallic state reflecting the spin-ladder structure is realized and the superconductivity possesses an s-wave-like character in the meaning that a finite gap exists in the quasiparticle excitation: At a pressure of 3.5 GPa, we observed two excitation modes in the normal state from the relaxation rate T-11. One gives rise to an activation-type component in T-11, and the other T-linear component linking directly with the superconductivity. This gapless mode likely arises from free motion of holon-spinon bound states appearing by hole doping, and the pairing of them likely causes the superconductivity.     

Pd addition in high Tc YBaCuO oxide

A small amount of Pd addition increases T_c for the YBa₂Cu₃O_7−y oxide. The maximum offset, midpoint and onset temperatures of the YBa₂(Cu_0.999Pd_0.001)₃O_7−y oxide are 92.1, 95.0 and 105 K, respectively. Excess addition of Pd decreases T_c. The T_c change is consistent with the results of the lattice constants.     

M3La(BO3)3(M=Ca,Sr,Ba)基质中Eu3+的光致发光

研究了M3La(BO3)3(M=Ca,Sr,Ba)基质中Eu3+的激发光谱和发射光谱.结果表明,最强激发峰均为394nm,并均有λ<300nm的较强电荷迁移带;按Ca-Sr-Ba的顺序,各发射峰峰值逐渐红移;Eu3+的最佳发射浓度分别为xEu3+=0.10、0.09、0.20;Eu3+的5D0→7F2跃迁发射的浓度猝灭机理分别为电偶极-四极、电偶极-偶极和电偶极-偶极相互作用.     

Relation of Structure and Superconductivity in Self-Compensating Y1-χCaχBa2-χLaχCu3Oy

The self-compensating compound of Y1-χ CaχBa2-χLaχ Cu3Oy is synthesized through a solid-state reaction method with χ from 0.25 to 0.55. Structural and superconducting properties have been investigated by χ-ray diffraction, Rietveld refinement, and dc magnetization measurement, respectively. The impure peaks appear when χ is more than 0.5 in the diffraction pattern. Orthorhombic-tetragonal transition occurs at χ = 0.45. Some local structural parameters, such as Cu（1）-O（4）, Cu（2）-O（4） bond lengths, change randomly in a narrow range. The relationship between the character of （Ba/La）-O plane and Tc is rather interesting. We attribute the behaviour of superconductivity to the joint effects of these local structural parameters. The results give the evidence that the influence of the structural change on superconductivity is essential and independent of carrier concentration.     

Study of the crystalline structure of the superconducting phase of the YBaCuO ceramic compound

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 Y_1.2Ba_0.8CuO_4−δ is orthorhombic type with crystallographic lattice constants a=0.3815 nm, b=0.3457 nm, c=2.650 nm.     

M2CeO4(M=Ca,Sr,Ba)的结构与发光特性

SSr2CeO4是一种新型的一维结构发光材料，其特殊的结构对其发光特性有决定性的作用。Sr2CeO4体系中可以顺利地进行能量传递，产生较强电荷迁移发光。合成了M2CeO4(M=Ca,Sr,Ba），发现与Sr2CeO4具有类似结构的Ba2CeO4也可以发光，而结构完全发生了变化的Ca2CeO4则不发光。