Tc Oxide Research Articles

Phonons and specific heat in high tc tl1(2)ba2Can−1Cuno2n+3(4) superconductors

Abstract A simple Born model involving a few adjustable parameters has been seen to explain very well the experimental data available for the Tl-based Tl1(2)Ba2an−1CunO2n + 3(4), n = 1 to 3 high — Tc oxide superconductors. In particular, for Tl2Ba2GaCu2O8 system the calculated phonon density of states is in very good agreement with the neutron data. The phonon bands show highly two-dimensional behaviour. Planar dispersions are significant only for the Gu-O2 layers. The lattice specific heat in the low temperature region shows a non-Debye behaviour i.e., a variation different from a T3 — one. This questions the reliability of the magnitude and the temperature dependence of the non — lattice contributions determined in an analysis of the observed total specific heat after assuming a T3 — dependent lattice contribution.

超伝導と高圧力 超伝導物質の衝撃圧力効果

Shock loading effects on various superconducting materials, placing emphasis on high Tc oxides, are summarized. Synthesis of superconductors via shock-induced phase transitions and chemical reactions, shock compaction of powder materials for fabrication of bulk superconductors, and shock deformation via defects and dislocations have been discussed. Shock loading effects and subsequent annealing effects on superconducting critical temperatures and flux pinning energy of high Tc oxides are elucidated.

Resistance and Current Density Studies on Plasma Sprayed Coatings of Bi(Pb)CaSrCuO Superconducting Materials

AbstractPlasma spraying is a potential technique for forming flexible tapes from brittle high Tc oxides. It is possible to obtain superconducting Bi(Pb)CaSrCuO coating by suitable heat treatment schedule after spraying. In an effort to get maximum transport current densities (Jc) of the coating, the content of lead and sintering time have been optimised. A Jc value of 200 Amp/cm2 is obtained in Bi1.4Pb0.6 · Ca2Sr1.9Cu3Oy specimen coated on silver sprayed Fe[(Ag)/Fe] substrate. Remarkable improvement in Jc values up to 694 Amp/cm2 is obtained in the same specimen coated on Ca2Sr1.9Cu3Oy sprayed Fe[Ca2Sr1.9Cu3Oy)/Fe] substrate. The observed decrease in Jc(B) curves with increase in magnetic field shows the presence of weak coupling between the grains.

Normal and inverse anomaly of dynamic current - voltage characteristics of high Tc oxide superconductors

This paper presents the experimental and theoretical results of investigations of the dynamic current - voltage characteristics of high T c oxide superconductors of various compositions. Measurements of normal and inverse peak effects have been carried out as a function of transport current amplitude, magnetic field sweep rate, polarization and temperature. Theoretical analysis of the phenomenon has been proposed based on detailed analysis of the asymmetry of the magnetic induction distribution on both sides of the sample caused by transport current flow. Calculations predicting the influence on the peak effect of the transport current amplitude and pinning centre concentration have been performed. Qualitative agreement with experimental data has been obtained for an Irie-Yamafuji-type pinning-force model. The inverse peak effect has been also experimentally established. This effect indicates similar behaviour to the normal one, for instance in respect to the dependence on the magnetic field sweep rate but opposite polarization.

Solution spinning of high Tc oxide superconductor: 1. Effect of propionic acid on the interaction between poly(vinyl alcohol) and copper (II) acetate

As basic research for the solution spinning of high T c oxide superconductor, the interaction between poly(vinyl alcohol) (PVA) and copper (Cu) (II) acetate in aqueous solution and in the solid state with and without propionic acid was studied. The interaction between PVA and Cu (II) ions in aqueous solution was extremely weak or non-existent. Complex formation of PVA with Cu (II) was observed in the solid state. The complex was changed from the co-ordination of the Cu (II) ion to the hydroxy groups on PVA to the Cu (II) ion complexing with two acetate ions and the hydroxy groups of PVA by adding propionic acid.

超伝導と高圧力 高温超電導と高圧力

The applications of high pressure to high - Tc oxide superconductors are reviewed. High pressure is very powewful for synthesizing of new materials and understanding of the physical properties. Studies of HIP treatment on Y124 and high pressure synthesis of “infinite - layer” materials are introduced. Pressure dependence of both Tc and Hall coefficients of the material are discussed in relation with carrier doping effects on the physical properties.

Magnetic hysteresis of p+ and 3He++ irradiated melt-textured YBa2Cu3O7−δ

We have measured the magnetic hysteresis loops and temperature dependent trapped fields in melt-textured YBa2Cu3O7−δ samples before and after p+ and 3He++ irradiation using a Hall effect magnetometer (HEM) as well as a commercial vibrating sample magnetometer (VSM). For proper 3He++ fluence, the critical current density may be enhanced by a factor of 10. Calculations based on various critical state models show that before the irradiation, the hysteresis loops can be well accounted for by a critical current density of a modified power law field dependence Jc(T,B)=J0(T)/(1+B/B0)n with n=1/2; after the irradiation, the best fit has been achieved by using an exponential form such as Jc(T,B)=J0(T)exp(−B/B0), where B0 is a model dependent parameter. Jc and its field dependence deduced from HEM hysteresis loops are in good agreement with those deduced from the VSM loops, suggesting that the Hall effect magnetometer can be conveniently used to characterize bulk high Tc oxide superconductors.

Simulation and interpretation of image contrast and diffuse scattering of tweed structure

The so-called tweed structure exhibits a roughly periodic lenticular-domain image (Fig.l) associated with the streaking of diffuse scattering around the fundamental reflections in an electron diffraction pattern (Fig.2(c)). Tweed was observed in high Tc oxides YBa2(Cu1-xMx)3O7-δ (M = Fe, Co, Al, x≥0.03; M = Cu, δ∼0.6-0.8), as well as in some binary alloys, which usually show statistical fluctuation in their composition or in an order parameter.Although tweed has long been studied, crystallographic aspects of tweed modulation is not well understood. To shed light on the details of the structure, we performed simulations both on the tweed image and diffuse scattering, based on our TEM observations of YBa2(Cu1-xMx)3O7-δ

On the combination of the Cooper pair and the Ogg pair in the high- Tc oxide superconductor

In this paper it is argued that the superconductivity of the high- T c oxide superconductor can be a combining mechanism of the Cooper pair and the Ogg pair. As a preliminary test the properties of the superconducting state of Bi 2Sr 2Ca 2Cu 3O 10 have been calculated under this mechanism. Further, within the framework of this combining picture a two superconducting energy gap structure may appear.

Some aspects of the thermodynamic behavior of high- Tc oxide systems via EMF and related measurements

EMF measurements of oxygen fugacities as a function of stoichiometry have been made in the YBa 2Cu 3O x , NdBa 2Cu 3O x , and Nd 1.81Ce 0.19CuO x superconducting systems in the temperature range 400–750°C by means of an oxygen titration technique with a yttria-stabilized zirconia electrolyte. The object of our current measurements is to investigate the effect of ionic size of Y, and Nd on the immiscibility and other structural transitions in the LnBa 2Cu 3O x system. The shape of the 400°C isotherm for Nd-Ba 2Cu 3O x indicates that, if a miscibility gap is present, it exists at lower temperatures and at values of x that are higher than those for the miscibility gap we deduce in the YBa 2Cu 3O x system. The relative locations of the miscibility gaps are consistent with the effects of ionic radii on the composition dependence of T c for these systems. Our results explain the two plateaus in measured values of T c as a function of composition for the YBa 2Cu 3O x system an appear to be consistent with the less pronounced T c plateau found for the NdBa 2Cu 3O x system at higher values of stoichiometry, partial pressures of oxygen above NdBa 2Cu 3O x are higher than for the YBa 2Cu 3O x system. Results of limited measurements on the n-type (electron-doped) superconducting Nd 1.81Ce 0.19CuO x system will be presented, as well as a thermodynamic assessment and intercomparison of our oxygen partial pressure measurements with the results of other measurements.

Normal state properties of high- Tc oxides

We discuss the expected behavior of normal state properties of high- T c oxides within the framework of the theory of hole superconductivity. The basic assumptions are: the normal state is a Fermi liquid, the bandwidth varies with carrier concentration, and the carrier concentration varies with temperature. We calculate the temperature and doping dependence of Hall number, resistivity, thermopower, magnetic susceptibility and nuclear spin relaxation rate, as well as the dependence of T c on the hole concentration at room temperature. Some of our results exhibit remarkable qualitative agreement with experiment. Experiments that would test the key prediction of bandwidth expansion with hole doping are discussed.

Restricted screening and non-adiabatic electron-phonon coupling in high- Tc oxides

The two-dimensional structure of typical high- T c oxides leads to weak screening of phonons which involve z-displacements and have energy larger than the electronic k z -dispersion. Frozen phonon calculations in which the screening is restricted show qualitatively the tendency for very large electron-phonon coupling of such modes. Models of non-adiabatic coupling suggest stable conditions for charge fluctuations and gaps from pairwise interactions of electronic states.

Antiferromagnetic spin fluctuations and superconductivity in high- Tc oxides

Anomalous physical properties of high- T c oxides as observed in the electrical resistivity, infrared conductivity, NMR relaxation rate, etc., above their transition temperatures are shown to be well explained in terms of antiferromagnetic spin fluctuations in two-dimensional metals described by the self-consistent renormalization (SCR) theory of spin fluctuations. Superconductivity due to the spin fluctuation mechanism is treated by using the weak coupling and the strong coupling theories. The order parameter is shown to be of B 1g character and the critical temperature is evaluated to be of the right order of magnitude.

Proximity effect in high- Tc oxide superconductors

The proximity effect in SNS (superconductor-normal conductor-superconductor) junctions composed of the oxides with isomorphic crystal structures is theoretically studied by using a simple model in which the S and N layers have similar electronic structures, and the superconducting pairing interaction works even in the N layer. The proximity effect is enhanced by the pairing interaction and the superconducting pair amplitude is connected between the S layers through the thick N layer which is primarily not superconductive due to a small number of holes. The proximity effects is almost unaffected by elastic impurity scatterings at low temperatures.

μSR and NMR measurements on high Tc oxides

Muons and NMR determine the phase diagram of high T c oxides. At the magnetic end they probe magnetization curves and the effect of hole doping on the order from a local point of view. In the superconducting phase they measure the London penetration depth, its temperature dependence and its correlation with the concentration of carriers.

精密マグネットシステムとその応用 金属材料技術研究所強磁場ステーションの建設

The development and applications of high resolution magnet system in National Research Institute for Metals are reported. The high resolution magnet system consists of three different sub-systems to cover various types of experiments under high resolution magnetic fields. The three sub-systems are designed for the detection of the quantum oscillations, for broad band solid state NMR experiments and for high resolution solid state NMR experiments, respectively. The purpose and specifications of each sub-system are described together with a brief introduction to each experiment. Typical examples of applications such as the de Haas-van Alphen effect of heavy Fermion compound UGe2, broad band solid state NMR of high Tc oxide and high resolution solid state NMR of 17O in Glycine are given to demonstrate the potentiality of the sub-systems.

Reply to Dr. F. Scholz's comments on ?determination of Pb4+ and Pb2+ in high Tc oxide superconductors?

Reply to Dr. F. Scholz's comments on ?determination of Pb4+ and Pb2+ in high Tc oxide superconductors?

Comment on ?Determination of Pb4+ and Pb2+ in high Tc oxide superconductors?, published by Namiki M, Hirokawa K (1990) Fresenius J Anal Chem 338:296?297

Comment on ?Determination of Pb4+ and Pb2+ in high Tc oxide superconductors?, published by Namiki M, Hirokawa K (1990) Fresenius J Anal Chem 338:296?297

Physico-chemical investigations on crystal growth of oxide superconductors

Single crystals provide a good form for studying of the relationship between the components, structure and properties of the high Tc oxide superconductors. The flux method has become the major way for obtaining the superconducting single crystals of reasonable size and quality. In this paper, a summary of the characteristics of oxide superconducting materials from physico-chemical point of view is given and some physico - chemical methods, especially thermal analysis, for assisting crystal growth is described. A general review is presented, which discusses the series of stages involved in the crystal growth and material science of oxide superconductors, including the synthesis and decomposition, crucible and starting materials, phase diagram and kinetic analysis, crystallization and dissolution, liquids and solubility, oxidation and reduction and dopants and stoichiometry.

Strong coupling effects in highz. sbnd; Tc oxides from paramagnons

While it is acknowledged, from both theoretical and experimental considerations, that the electron-phonon mechanism is not responsible for the superconductivity in the high z. sbnd; T c oxides, several experiments remain which exhibit strong-coupling effects. This paradox can be resolved by considering a mechanism for the high z. sbnd; T c oxides which is mainly electronic in origin but with a small contribution from the electron-phonon interaction and a significant contribution from dynamic spin fluctuations, paramagnons. In such a model, strong coupling effects can arise from the paramagnons. Fixing the electron-phonon contribution to achieve an isotope effect coefficient of 0.05 at a T c of 96K, we can obtain a large gap ratio, 2 Δ 0/ k B T c , a two-fluid model-like temperature dependence for the penetration depth, and a featureless optical conductivity, σ S / σ N , in agreement with interpretation of experiment.