Toshihiko Maeda

Transport properties of the Pb-based superconducting cuprate (Pb1+x/2Cu1-x)Sr2(Y1-xCax)Cu2Oy

Abstract The resistivity, Hall effect and Seebeck effect of (Pb (1+ x )/2)Sr 2 (Y 1- x Ca x )Cu 2 O y ( x ⩾0.35) were determined. Superconductivity appeared only for x =0.30 and 0.35 and only when the sample was quenched from high temperature. Transport data showed that hole carriers increase with x and with decreasing oxygen content, y , from 7.1 to 7.0 by quenching. This indicates that, unlike the case of “Tl-1212”, the “Pb-1212” system cannot be explained by over-doping arguments. Positive magnetoconductance was observed for the slowly cooled sample with x =0.35. Substitution and quenching effects on the transport properties are discussed from the viewpoints of self-doping, charge transfer and localization.

In-plane textured oxide buffer layer for the TFA-MOD method on 〈100〉{001} Ni tapes using MOD process

We developed a low cost process, the so-called all-MOD process, whereby we used MOD to deposit both YBCO and oxide buffer layers on {100}(001) Ni tapes. Highly in-plane textured and crack-free Ce-Gd-O (CGO) buffer layers on the cube-textured Ni tapes were achieved by the MOD process. Highly in-plane textured YBCO films on the CGO-buffered Ni tapes were also observed. Long tapes were made by applying a 1 m long CGO buffer layer on the Ni tapes and firing in a batch-type furnace. The CGO films were made by a continuous bead coating process and firing under an Ar-H 2 atmosphere. The 1 m CGO-on-Ni tape was highly in-plane textured. R 1 ( 2 0 0 ) and FWHM of phi-scan values were 88-96% and 7.0-8.5°, respectively. We determined the degree of (n00)-orientation: R l ( n 0 0 ) [≡I ( n 0 0 ) /{I ( n 0 0 ) + I ( m m m ) } x 100(%)], where I ( n 0 0 ) and J ( m m m peaks represent the X-ray θ-2θ scan intensities. These results indicate that buffered Ni tapes made by the MOD process are useful for TFA-MOD fabrication of long-length YBCO coated conductors.

Advances in surface-oxidation epitaxy processed substrates for YBa2Cu3O7−δ film

Abstract The preparation of long oxide template using surface-oxidation epitaxy (SOE) method and the deposition of oxide cap layer and YBa 2 Cu 3 O 7− δ (YBCO) film on it have been studied for the fabrication of coated conductors. In SOE process, Cr-oxide behaves as a barrier against Cr contamination with SOE-NiO layer in high strength and low magnetism Ni-clad Ni–20wt.%Cr (Ni/NiCr) tape. MgO cap layer makes SOE-processed tape surface smooth with the average roughness of a few nm. The critical current ( I c ) of 8 A (the critical current density ( J c ) of 0.2 MA/cm 2 ) was obtained for the YBCO film deposited on a 10 cm long×5 mm width SOE-processed tape with MgO cap layer in a short sample cut from a 10 cm long specimen. J c exceeding 0.1 MA/cm 2 was obtained for YBCO film on SrTiO 3 cap layer and CeO 2 one of SOE-processed tape.

Characterization of Biaxially Textured Ni-Based Alloy Substrates

15m long textured nickel tapes were prepared as a possible substrate for epitaxial NiO growth by recently proposed surface-oxidation epitaxy (SOE) method. As cold-rolling and subsequent recrystallization heat treatment were properly done, that we obtained a highly {100} textured structure throughout the whole length of tapes. Since relatively low mechanical strength and ferromagnetism of nickel have been pointed out to be severe drawbacks for wire application, two kinds of Ni-based alloys, Ni-Cr and Ni-V, were investigated from the view point of magnetization and tensile mechanical property. It is shown that, compared with the case of pure nickel tape, both Ni-12wt%Cr and Ni-10wt%V tapes were much stronger and exhibited one order of magnitude smaller hysteresis loss.

High-Pressure transport phenomena in (Pb(1+x)2Cu(1−x)2)Sr2(Y1−xCax)Cu2O7+δ

Abstract Pressure effect on Tc for “Pb-1212” phase is investigated up to 2GPa using a piston- cylinder apparatus. Unusually large pressure coefficient of Tc is observed ( dln T c d p =0.65 GPa −1 , Tc=16.8K at latm.). Pressure induced-delocalization of holes is discussed.

Synthesis and 57Fe Mössbauer Spectroscopy of (Pb0.5Fe0.5)Sr2(Y0.5Ca0.5)Cu2Oz (z ≈ 7)

A nonsuperconducting lead cuprate having the “1:2:1:2” structure and a nominal composition of (Pb0.5Fe0.5)Sr2(Y0.5Ca0.5)Cu2Oz is synthesized as a single-phase polycrystalline form. The temperature dependence of electrical resistivity is slightly metallic at temperatures around 300 K, but it increases after an annealing at 800°C in air and subsequent quenching into liquid N2. The 57Fe Mossbauer spectroscopy is performed in order to discuss the site distribution of Fe atoms.

Fabrication of RE123 coated conductor using LPE process

Abstract We have tried to apply the liquid phase epitaxy (LPE) process to fabricate RE123 coated conductors. We have developed the architecture using a BaZrO 3 buffer layer, called “non-reactive buffer type” on a textured Ni substrate. In the previous study, RE123/BaZrO 3 /NiO/Ni sample was shown that T c value was about 90 K, however the J c value was lower than 10 3 A/cm 2 . In order to increase J c of the film, the perfect coverage on of the BaZrO 3 on the substrate has to be attained. Then, we tried to grow a BaZrO 3 buffer layer directly on a textured Ni substrate without formation of the NiO layer to maintain good in-plane alignment. The alignments of the BaZrO 3 layer and the seed layer become better in this architecture, and the linkage of LPE grains was improved. Consequently, the sample of Y–Yb/BaZrO 3 /Ni revealed the T c value of about 90 K and the I c value of 12 A.

Texture study of YBa2Cu3O7−δ films on NiO templates for wire application

Abstract Texture behavior and superconductivity of pulsed-laser-deposited YBa 2 Cu 3 O 7− δ (YBCO) films on biaxially textured NiO templates are investigated. Texture of the YBCO films deposited on (1xa00xa00) NiO surface of single crystal is found to be vary from the “cube-on-cube” type to the “45° rotation” type as substrate temperature increases. High values of critical current density ( J c ) of 3.3 MA/cm 2 (1 μV criterion) and 1.0 MA/cm 2 (1 μV/cm criterion) at 77.3 K are achieved respectively for YBCO film on NiO single crystal and for that on BaZrO 3 -capped NiO buffer layer formed by the surface-oxidation-epitaxy technique. However, YBCO films deposited onto a moving substrate exhibit much lower J c and texture of the low- J c films is found to be different from that of high- J c ones.

Mössbauer Analysis of 57Fe Substituted for Cu in 1212-Phase (Pb,Cu)Sr2(Y,Ca)Cu2Oz Superconductor

57Fe Mossbauer effect in the 1212-phase superconductor is studied by comparison with that in the 123-phase. Spectra at room temperature consist of three doublets (Dl with Δ = 0.56 mm/s, D2 with 1.01 mm/s, D3 with 1.80mm/s), and two antiferromagnetically split sextets (S1 with H i ,= 472 kOe, S2 with 381 kOe) are observed at low temperatures. D3(= S1) attributes to Fe4+ (S = 2) at Cu(1) site and D1(= S2) do to Fe3+ (S=5/2) at Cu(2).

Flexible Cable Carrying Superconducting Current Over 500A at 77k

With an aim of making a study on the possible application of an oxide superconducting wire to a power cable, a flexible model conductor was fabricated by using Bi-based multifilamentary silver sheathed tape wires. The conductor was composed of tape wires which were spirally wound at a pitch of 250mm around a former having outer diameter of 25mm. The prototype conductor was proved to have the value of Ic which was equal to the total of Ic of each wire at the temperature of liquid nitrogen (77K), and without the external magnetic field and it showed no fall in Ic due to its being wound up. It also proved that its Ic did not fall even if it was subject to repeated bending of up to maximum 100 times at the same bending strain ratio, when it underwent bending of the maximum radius of 1m (corresponding to the bending strain rate of 2.2%). Same results were obtained even if an insulation layer was constructed on the surface of the conductor.