high-Tc Oxide Superconductors Research Articles

Current status on the superconductivity research in Korea

Superconductivity research in Korea was firstly carried out by a research group in Seoul National University(SNU}, who fabricated a small scale superconducting magnetic storage system under the finantial support from Korea Electric Power Company(KEPC0). But few sicentists were involved on superconductivity research until the oxide high Tc superconductor was discovered by Bednorz and Mueller Ii. After the discovery of YBaCuO superconductors operating above the boiling point of liquid nitrogen( 77K ) ‘I, Ministry of Science and Technology( MOST ), Korea, recognizing the importance of high Tc technology, donated a special fund for the superconductivity research to universities and government supported research institutes. Scientists engaged in this project organized ‘High Temperature Superconductivity Research Association{ HITSRA )’ to achieve the project goal efficiently. Its major functions are to coordinate research activities on high Tc superconductivity and to distribute research

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.

The Recent Trends of High Temperature Superconductors. VI. Application for Magnetic Shielding System Using High-Tc Oxide Superconductor.

The Recent Trends of High Temperature Superconductors. VI. Application for Magnetic Shielding System Using High-Tc Oxide Superconductor.

Flux and Charge Quanta in Junctions and Macroscopic Quantum Effect

A study is made on the physical conditions of the appearance of the Josephson effect and the single-charge effect in the junctions of superconductor and normal metal. When the electrodes of a bridge junction are made of high-Tc oxide superconductor, and the bridge part is made of highly resistive material of a kind of oxide similar to the superconductor, a single charge-quantum device with working temperatures up to Tc can be realized with a relatively large device size.

Helmet-size vessels of high-Tcoxide superconductor for magnetic shield

Abstract We have developed a very large magnetic shielding vessel made from high-Tc Bi-Pb-Sr-Ca-Cu-O superconductor and have experimentally confirmed that this vessel can reduce a weak magnetic field to -100 dB or 1/105. The size of this vessel is 32 cm in diameter, 64 cm in depth and 2.5 cm in thickness. The shielding effect of the vessel does not decrease even at a low frequency like 0.2 Hz. The high attenuation ratio in the low frequency range indicates that magnetic shielding using a high-Tc superconductor is promising for neuromagnetic measurements with SQUID.

Temperature dependence of Hall coefficient in high-Tc oxides

Large Fermi surfaces obtained by the local-density band-structure calculation are consistent with signs of the Hall coefficient obtained by experiment for almost all high-Tc oxide superconductors. However, a simple band-electron picture cannot explain the large temperature dependence of the Hall coefficient. We propose a phenomenology for the temperature dependence of the Hall coefficient, and discuss the origin of temperature dependences of transport coefficients.

Spectral photoconductivity of the BaPb1-xBixO3system with a proposal for the electronic structure

Abstract A series of systematic studies of transient photoconductivity has been made on the BaPb1-x Bi x O3 system in the semiconductive phase. On the basis of the new experimental results, we propose a new model for the electronic structure and the optical transitions for the BaPb1-x Bi x O3 system in the semiconductive phase in a consistent way together with the previous data. The semiconductive nature of BaBiO3 is attributed to its electronic structure, essentially similar to that of Bi2O3 with localization of an excess hole on the O2- ion per formula unit of BaBiO3. This model is different from one based on the splitting of the Bi–6s state due to local charge-density-wave formation. If we extend the proposed electronic structure to cover that of the superconductive phase, we obtain a resultant electronic structure similar to those of the Cu-based superconductors, at least near the Fermi level. Thus, we recognize that this feature may reveal a common mechanism for both Cu-based and BiO-based high-Tc oxide superconductors.

The improvement in magnetic shielding by use of a double-cylinder configuration of high-Tc oxide superconductors

The critical current density (Jc) of high critical temperature (Tc) copper-oxide superconductors is an important parameter in magnetic shielding. However, it was determined that the value of Jc was not closely related to the degree of magnetic shielding. The degree of shielding can be improved by the use of a configuration of superimposed double cylinders constructed of a copper-oxide superconductor. Experimental results indicate that the characteristics of the double-cylinder system (such as the effect of the excitation magnetic field on the magnetic field within the cylinders, and the distribution of the magnetically shielded field along the axial direction of the cylinders) are improved over those of single superconducting cylinders.

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.

On Electronegativity of the High-Tc Oxide Superconductor

Using a very useful quantity in physics and chemistry, the electronegativity, we have found that for nearly 70 high-Tc oxide superconductors (HTOS), the average electronegativity is in a narrow range 2.5-2.7. The difference of bond character between the HTOS and the conventional superconductors has been discussed. Finally, two categories of superconductors in terms of the group average electronegativity are suggested.

Novel field-induced asymmetry in the remanent magnetization of the superconductor YBa2Cu3O7

THE dynamics of trapped vortices of magnetic flux in the high-Tc oxide superconductors have been much studied1–4, but remain poorly understood; in particular, we have much to learn about vortex 'creep' at low temperatures. Using a scanning Hall micro-probe to measure directly the spatial and temporal variation of the flux density in YBa2Cu3O7 single crystals, we have uncovered a remarkable asymmetry in the magnetization profile, which is induced by the direction of the field (applied normal to the a–b crystal face). The external field imparts a rotation to the vortex motion, which strongly distorts the remanent profile away from the form predicted by conventional critical-state models5. This rotation was not anticipated and, to our knowledge, is not accounted for in existing theories.

Changes of Superconductivity and Crystal Structure on Ba2YCu3O7-x Thin Film by 2.5 MeV Ni2+ Ion Irradiation

Effects of 2.5 MeV Ni2+ ion irradiation on thin films of high-Tc oxide superconductor Ba2YCu3O7-x were investigated in the fluence range 1.0×109 cm-2<φt<3.0×1014 cm-2. An increase of transport Jc due to irradiation was observed below 1.0×1010 cm-2 in φt, while above this fluence, both Tc and Jc decreased. In X-ray diffraction (XRD) measurement, decrease in intensity and increase in the full width at half maximum (FWHM) value of peaks and in the c-axis lattice constant were observed above 1.0×1013 cm-2 in φt.

Effects of ionic radius on structure and superconductivity for high-Tc oxide superconductors

The effects of the ionic radius on structure formation and superconductivity are studied for the Bi2Sr2Ca0.8R0.2Cu2Oy system (R = rare earth elements except Ce, Pr, Pm, and Tb). The results are compared with those on the RBa2Cu3Oy system. The crystals grown have the nominal composition BiSr0.85Ca0.8R0.5Cu1.5Oy (R = the above-mentioned rare earths and Cd). It is found that the crystals including R with ionic radius less than that of Ca form the 2212 phase; the crystals including R with ionic radius larger than and similar to that of Ca form the 2201 phase. All results are explained from the crystallochemical point of view. It is found that superconductivity is related to the structure stability. Der Effekt des Ionenradius auf die Strukturbildung und die Supraleitfahigkeit wird fur das System Bi2Sr2Ca0,8R0,2Cu2Oy (R = seltenes Erdelement auser Ce, Pr, Pm, Tb) untersucht. Die Ergebnisse werden mit denen fur das RBa2Cu3Oy-System verglichen. Die gezuchteten Kristalle haben die nominelle Zusammensetzung Bi2Sr0,85Ca0,8R0,5Cu1,5Oy (R = eine der obengenannten seltenen Erden oder Cd). Wenn der Ionenradius von R kleiner ist als der von Ca, wird die 2212-Phase gebildet, ist der Ionenradius von R groser als der von Ca, entsteht die 2201-Phase. Alle Ergebnisse werden aus kristallchemischer Sicht erklart. Es wird gefunden, das die Supraleitfahigkeit mit der Stabilitat der Struktur in Beziehung steht.

On the characteristic lengths of the highTcoxide superconductors

Abstract We discuss the fundamental characteristic lengths, namely ζ0 the zero temperature coherence length, ΛL the London penetration depth, and l the carrier mean free path, for the oxide high Tc superconductors in relation to the latest experimental measurements. We examine theoretically why ζ0 is so small and argue that its smallness is independent of the nature of the pairing mechanism of superconductivity. We also compare various measurements from the point of view of Pippard's theory for both the normal and the superconducting states respectively. Several questions are posed by these interpretations of the experimental data.

Phase transitions in the system Ba-K-Pb-Bi-O

Abstract Ba(Pb, Bi)O3 is known to be a superconductor for appropriate concentration of bismuth. On the other hand, all known high-Tc oxide superconductors show two-dimensional sheet structures. In an hypothetical Ba2(Pb,Bi)O4 system, both ingredients would be combined. The latter system is found to exist, isostructural to La2CuO4, but being an insulator. This paper shows how to induce an insulator-metal phase transition in this series by potassium doping. The electronic carrier concentration is checked by screening of phonons in infrared reflectivity spectra.

Magnetic hysteresis effects in high-Tc oxide superconductors

Magnetic irreversibility in high-Tc yttrium-based compounds prepared in air has been investigated. The measurements of full and minor hysteresis loops of magnetization curves, flux trapping and flux creep effects were performed at liquid helium temperature. The authors developed a new method of determining critical current density from minor hysteresis loops. In the flux trapping experiments they observed an anomalous behaviour of the remanent moment for the samples doped with an iron impurity. The lower critical field was estimated from those measurements. The magnitude of the pinning potential as well as the activation energy for the flux creep effect was also determined.

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

ANALYSIS OF THE HIGH Tc OXIDE SUPERCONDUCTORS FROM THE GOLDEN COORDINATES

In this paper, more than sixty high-Tc oxide superconductors are analysed again with Vil-lars coordinates. Moreover, we introduce two new coordinates, namely, the average electrone-gativity and chemical combination valence. It is found that the high-Tc oxide superconductors are distributed more concentratively in the diagram of these new coordinates.