Kunio Matsuzaki

High Tc Superconductor Prepared by Oxidization of a Liquid-Quenched Yb1Ba2Cu3 Alloy Foil in Air

An Yb1Ba2Cu3 alloy foil with a nonequilibrium structure including an amorphous phase was prepared by splat-quenching. Heating of the alloy foil in air resulted in the structural change to a crystalline metallic phase at about 490 K, followed by the oxide formation of Yb1Ba2Cu3O6.8 at temperatures above about 540 K. The Yb1Ba2Cu3O6.8 prepared by oxidization of the liquid-quenched alloy foil was found to exhibit high Tc superconductivity with onset at 91 K and zero resistance at 85 K, even though the Jc value at 4.2 K was as low as about 1.9 A/cm2 in the absence of applied field and 0.4 A/cm2 at H=7 T.

Microstructure and superconducting properties of melt-quenched insoluble Al-Pb and Al-Pb-Bi alloys

In order to obtain aluminium-based superconducting alloys including finely dispersed lead or Pb-Bi particles, the application of the melt-quenching technique has been tried for Al-Pb, Al-Si-Pb and Al-Si-Pb-Bi alloys containing immiscible elements such as lead and bismuth. It has been found to result in the preparation of superconducting materials consisting of fcc Pb or h c p ε(Pb-Bi) particles dispersed finely and densely in the aluminium-based matrix in each composition range below about 2 at % Pb for Al-Pb alloys and 5 at % Pb or (Pb + Bi) for (Al0.9 Si0.1)100−x Pbx and (Al0.9Si0.1)100−x (Pb0.6Bi0.4)x alloys. The particle size and interparticle distance were ∼ 40 nm and 40 to 100 nm, respectively, within the grains, and ∼ 100 nm and below ∼ 30 nm, respectively, at the grain boundaries for the lead phase in Al98 Pb2 alloy. Particle size was ∼ 15 to 60 nm and interpartide distance 30 to 60 nm for the Pb- Bi phase in (Al0.9 Si0.1)95(Pb0.6 Bi0.4)5 Transition temperature,Tc was 4.16 K for Al98Pb2, 3.94K for (Al0.9Si0.1)95 Pb5 and 7.75 K for (Al0.9Si0.1)95(Pb0.6Bi0.4)5. The upper critical magnetic field,Hc2, and critical current density,Jc, for (Al0.9Si0.1)95(Pb0.6Bi0.4)5 were 0.22 T at 4.2 K and 1.67 × 107 Am−2atzeroappliedheld and 4.2 K. The appearance of the superconductivity for the aluminium -based alloys was interpreted as due to the formation of superconducting percolation path along the tangled dislocations, sub-boundaries and/or grain boundaries where Pb and Pb-Bi phases precipitated preferentially.

Preparation of a High Tc Superconductor by Oxidization of an Amorphous La1.8Sr0.2Cu Alloy Ribbon in Air

A ductile La1.8Sr0.2Cu amorphous alloy with a long ribbon shape was prepared by melt spinning. Oxidization of the amorphous alloy ribbon at 1173 K for 1.2 ks in air results in formation of a tetragonal (La1.8Sr0.2Cu)xOy, oxide. Furthermore, the oxide ribbon was found to exhibit high Tc superconductivity with onset at 36 K, midpoint at 22 K and zero resistance at 9 K. It is therefore concluded that the new process consisting of the preparation of an amorphous alloy ribbon with good ductility, followed by the high temperature oxidization in air is useful for production of a superconducting oxide tape with high Tc.

Production of Bi–Sr–Ca–Cu–O Glasses by Liquid Quenching and their Glass Transition and Structural Relaxation

New BiSrCaCu2Oy and Bi1.3SrCaCu2Oy oxide glasses were produced by the single roller melt-spinning technique. The glasses were found to translate into a supercooled liquid accompanied with a distinctly appreciable glass transition at about 680 K, followed by crystallization at about 725 K. The increase in Bi content brought about a decrease in glass transition temperature and an increase in crystallization temperature, i.e. the extension of the supercooled liquid region. Specific heats of the glassy solid and the supercooled liquid and the difference in specific heat between the two states were measured for the two oxide glasses.

Electrical Resistance in Superconducting Amorphous Alloy Zr70Ir30

Results for the electrical resistance of the superconducting amorphous alloy Zr 70 Ir 30 (ρ=300 (mu varOmega cdot)cm and T c =3.67 K) are reported. The resistance increases by amount of 3.7% on cooling from 300 K down to 10 K where it shows a hump, and then decreases rapidly approaching to T c . Above 27 K any magnetoresistance (MR) is not detected, but, in 1.7 K ≦ T ≦27 K, the positive MR is observed and becomes saturated above H s =12–13 T . The saturated resistance in H ≧ H s is greatly enhanced on cooling with a singular dependence, - log T . The para-conductivity near T c due to the superconducting fluctuation is explained by the Aslamasov-Larkin term, indicating an absence of the Maki-Thompson mechanism.

Preparation of nickel-based amorphous alloys with finely dispersed lead and lead-bismuth particles and their superconducting properties

The application of the melt-quenching technique to Ni-Si-B-Pb, Ni-P-B-Pb, Ni-Si-B-Pb-Bi and Ni-P-B-Pb-Bi alloys containing immiscible elements such as lead and bismuth has been tried and it has been found to result in the formation of a new type of material consisting of fine fcc Pb or hcp ɛ(Pb-Bi) + bct X(Pb-Bi) particles dispersed uniformly in the nickelbased amorphous matrix. The particle size and interparticle distance were 1 to 3 and 1 to 4 µm, respectively, for the lead phase, and less than 0.2 to 0.5 µm and 0.2 to 1.0 µm for the Pb-Bi phase. The uniform dispersion of such fine particles into the amorphous matrix was achieved in the composition range below about 6at% Pb and 7at% (Pb + Bi). Additionally, these amorphous alloys have been found to exhibit a superconductivity by the proximity effect of f c c Pb or ɛ(Pb-Bi) superconducting particles. The transition temperatureTc was in the range 6.8 to 7.5 K for the Ni-Si(or P)-B-Pb alloys and 8.6 to 8.8 K for the Ni-Si (or P)-B-Pb-Bi alloys. The upper critical fieldHc2 and the critical current densityJc for (Ni0.8 P0.1 B0.1)95 Pb3 Bi2 at 4.2 K were, respectively, about 1.6T and of the order of 7 X 107 A m−2 at zero applied field. Melt quenching of amorphous phase-forming alloys containing an immiscible element has thus been demonstrated, enabling us to produce amorphous composite materials exhibiting unique and useful characteristics which cannot be obtained in homogeneous amorphous alloys.

Upper Critical Fields on High Temperature Superconductivity in La–Sr–Cu–O System

The electrical resistances of three La-Sr-Cu-O samples prepared by different methods have been measured undermagnetic fields up to 20.3 tesla between 4.2 and 50 K. The upper critical fields were determined by the midpoint of the resistive transition. The largest slope of the critical field was -2.7 T/K for a sintered sample La1.85Sr0.15CuO4. According to the Werthamer, Helfand and Hohenberg expression in the dirty limit, the upper critical field Hc2(0) was estimated to be 71 T. Various superconducting and normal states properties are derived.

High-Tc Superconductor Produced by Oxidization of Melt-Spun Ag-Ho-Ba-Cu Alloy Ribbon

A (Ho0.17Ba0.33Cu0.5)50Ag50 alloy ribbon with a non-equilibrium structure was produced by melt-spinning. Heating of the alloy ribbon in air brought about the structural change to a stable metallic phase at about 610 K, followed by the formation of Ho1Ba2Cu3O6.7 and Ag in the range of 630 to 740 K. The mixed materials of Ho1Ba2Cu3O6.7 and Ag produced by oxidization of the melt-spun ribbon exhibited high-Tc superconductivity with onset at 90 K and zero resistance at 80 K. It is notable that the mixture of Ag enables us to produce an alloy ribbon by melt-spinning even in the Ho-Ba-Cu alloy system with large miscibility gap.

Anomalous electrical resistive behaviour of Al-O-Pb sputtered alloys

Application of the sputtering technique to (Al-O)x Pb100-x alloys containing an immiscible lead element has been found to result in the formation of a duplex material consisting of f cc lead particles dispersed in an amorphous AlxOy oxide matrix. The particle size and interparticle distance of the lead phase were about 10 to 50 nm and 10 to 40 nm, respectively. The Al-O-Pb alloys have been found to exhibit an extremely high electrical resistivity (ϱ), e.g., 4.06 x 106 μΩ cm for (Al-O)87.5 Pb12.5 at 273 K, as well as a large positive temperature-dependent resistivity reaching 92% Of ϱ273. The peculiar resistivity behaviour was interpreted by assuming the mechanism that only the lead phase embedded in AlxOy matrix contributes to electrical conductivity and the mobility of lead electrons is greatly reduced in the intervening oxide region among lead phases. It has thus been demonstrated that the composite material exhibiting peculiar characteristics, which cannot be achieved in metallic composite materials, is obtained by simultaneously sputtering oxide and an insoluble metallic element.

Layered Structure and Superconducting Properties of Ag-Sheathed Bi1.84Pb0.34Sr2Ca2Cu3Oy Wires Prepared by Combined Jellyroll and Hotextrusion Technique

The superconducting wires were prepared by hotextrusion of a billet of jellyroll form. The wire exhibited a layered structure of Ag and Bi2223 oxide. Critical current density (J c) increased with decreasing diameter of extrusion die and the highest J c value for the wire with 2 mm diameter is 3200 A/cm2 at 77 K and 18000 A/cm2 at 4.2 K. These rather high J c values are due to the increase of the interface area between Ag and oxide resulting from the decrease in the thickness of the oxide layer. This method seems to be a useful way of obtaining the superconducting wire with a round shape for the Bi2223 oxide.