Atsutaka Maeda

In situ growth of Bi-Sr-Ca-Cu-O thin films by molecular beam epitaxy technique with pure ozone

Thin films of Bi-Sr-Ca-Cu-O have been grown in situ on SrTiO3 (001) substrates using a molecular beam epitaxy technique with a pure ozone source. This allows us to grow highly oriented films at substrate temperature of 700°C without heat treatment in oxygen. One of the films showed a superconducting transition at 10.0 K.

High Temperature Superconductivity at 90 K in Orthorhombic LaBa2Cu3Oy

A LaBa2Cu3Oy sample with an orthorhombic crystal structure was synthesized. It showed superconductivity with an onset temperature of 95 K and zero resistance at 80 K (midpoint 90 K). From the magnetic susceptibility measurement, about 30% of the whole volume of the sample was found to be the 90 K superconducting phase. The 90 K superconducting phase in LaBa2Cu3Oy is thus considered to have an oxygen defect perovskite structure which is most probably identical to that of the typical 90 K superconductor orthorhombic YBa2Cu3Oy.

1/f conduction noise in the high-temperature superconductor Bi-Sr-Ca-Cu-O system

Abstract Conduction noise was investigated in the normal state of the 2212 phase of the Bi-Sr-Ca-Cu-O system for polycrystals, highly oriented thin films, and single crystals. It was found that large noise with 1/ f spectrum in this material is generated as a bulk effect. The magnitude of the noise power is 7–10 orders of magnitude larger than in normal metals even in single crystals. Several possible origins are discussed.

Threshold-field behavior and switching in K0.3MoO3

Abstract Nonlinear conductivity in K 0.3 MoO 3 is measured down to 18 K. The threshold field of the nonlinear conduction, after having a minimum value around 50 K, increases with decreasing temperature, and then drastic delayed switching with a threshold field of the order of 100 V/cm is observed. In the switching, undamped regular oscillations between the pinned and depinned states of charge density wave can be seen, which suggests the existence of the well-defined depinned states in blue bronze.

Study on the Preparation and the Physical Properties of a 110 K (Bi, Pb)2Sr2Ca2Cu3Oy Superconductor

High-quality samples of 110 K superconductor (Bi, Pb)2Sr2Ca2Cu3Oy were prepared in a single-phase polycrystalline form, which show resistivity at room temperature below 1 mΩcm and a zero-resistance temperature of 107 K. The Hall coefficient and the plasma frequency were measured in these crystals. The Hall coefficient and the plasma frequency obtained were 1×10-3 cm3/C and 8700 cm-1, respectively.

Study on the preparation of 90‐K superconductor LaBa2Cu3Oy

The high‐Tc superconductor LaBa2Cu3Oy has been prepared under various conditions, and characterized by x‐ray and neutron powder diffraction techniques, dc and ac magnetic susceptibility measurements, and dc resistivity measurement. It has been found that samples with excellent superconducting characteristics and also with good structural properties are obtained in a reproducible way if the following three procedures are performed: preheat treatment of La2O3 powders, sintering in N2, and low‐temperature annealing in dried O2. Long‐time annealing in undried O2 was sometimes found to degrade the grain boundaries and to lead to a lower zero‐resistance temperature.

Epitaxial Growth of Bi-Sr-Ca-Cu-O Thin Films by Molecular Beam Epitaxy Technique with Shutter Control

Thin films of Bi2(Sr, Ca)3Cu2Oy have been prepared in situ by a molecular beam epitaxy technique in an ozone atmosphere of 4×10-4 Pa. The molecular beams were shutter controlled and films were deposited layer by layer. In situ reflection high energy electron diffraction (RHEED) showed the formation of the perovskite-related structure even at the initial deposition (one unit cell). The resistance of one of the films became zero at 30 K without heat treatment in oxygen.

Transmission Electron Microscopy of Modulated Structures in Pb-Doped BSCO Superconductors, Bi2.1-xPbxSr1.9CuOy (x=0 to 0.3)

Crystal structures of Pb-doped BSCO superconductors, Bi2.1-xPbxSr1.9CuOy with x=0 to 0.3, are examined by transmission electron microscopy. Compounds with x from 0.05 to 0.2 exhibit satellite reflections in b*-c* electron diffraction patterns in a different manner from the x=0 compound, indicating formation of modulated structures similar to those observed in Pb-doped BSCCO superconductors. Modulation periodicity increases with increase of Pb content x. The compound with x=0.3, however, shows no satellite reflections suggesting the absence of modulation at high Pb content.

Effect of substitution of 3d metals for Cu in Bi2(Sr0.6Ca0.4)3Cu2Oy

Abstract The effect of the substitution of 3d metals (Fe, Co, Ni and Zn) for Cu was investigated. Lattice constants, DC resistivity, Hall effect, magnetic susceptibilities in normal and superconducting phases were measured. The change of the Hall coefficient with the substitution was much smaller than those in YBa 2 Cu 3 O y or in Y or lanthanide substituted Bi 2 (Sr, Ca) 3 Cu 2 O y . The change of T c with the substitution of Fe, Co, Ni with localized magnetic moment did not differ much from that of Zn with no magnetic moment.

Tetragonal-to-orthorhombic transition and disappearance of superconductivity in the Pb-doped Bi2Sr2CuOy system

A series of superconductors Bi2.1-xPbxSr1.9CuOy with 0.05≤x≤0.5 were synthesized in polycrystalline form. Tetragonal to orthorhombic transition was found at around x=0.1. By the introduction of Pb, it was found that the average valence of Cu increases, whereas the superconducting transition temperature decreases. The system becomes more metallic with increasing x.