Hideo Fujiki

Superconductivity in the Bi−Sr−Cu−O system

A superconducting transition with an onset temperature near 8 K was observed for the Bi-Sr-Cu-O system through electrical resistivity and magnetic susceptibility measurements. The superconductivity is of a bulk nature and reproducible.

Successive magnetic phase transitions in Nd2CuO4

A neutron scattering study on Nd 2 CuO 4 , a mother material of the electron-doped superconductor (Nd 1- x Ce x )CuO 4- y , was carried out. Reentrant magnetic phase transitions associated with spin reorientation of antiferromagnetic ordering were observed. La 2 NiO 4 -type order was stabilized in the range 80 K\({\lesssim}T{\lesssim}\)250 K and at \(T{\lesssim}40\) K. Between 40 K\({\lesssim}T{\lesssim}\)80 K, La 2 CuO 4 -type order was realized. Diffuse scattering due to the two-dimensional spin fluctuation was also observed at around T ≃250 K.

Crystal Substructure of the Bi-Sr-Cu-O System

A substructure with a pseudotetragonal unit cell is proposed for a low-Tc superconducting oxide Bi-Sr-Cu-O system on the basis of Rietveld analysis of powder X-ray diffraction data. It is a layered structure having the composition Bi2Sr2CuOy. The relationship between the crystal structure of the Bi-Sr-Ca-Cu-O system and that of Bi-Sr-Cu-O system was discussed.

Experimental Evidence for Nanostructural Tube Formation of Silicon Atoms

The presence of silicon nanotubes (SiNTs) composed of rolled-up quasi-two-dimensional honeycomb nets was first revealed by transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron diffraction analysis, among products synthesized using a simple laser ablation technique. They were coaxial multiwall high-purity SiNTs with cylindrical symmetry, smallest inner and outer diameters of 1 and 4 nm, respectively, lengths up to ~1 µm, and an interwall distance of 0.36 nm.

Long Period Structures in the Bi-Sr-Cu-O System

The structure of the superconducting Bi-Sr-Cu oxide system was studied by means of electron diffraction. Three kinds of long period structures were found in this system. The relation between these long period structures and the nonstoichiometry in this system is discussed.

A Side-Entry Helium-Cooled Stage for Electron Microscopy

A liquid-helium-cooled specimen stage for an electron microscope has been designed and built. It attaches to the microscopes side-entry goniometer and contains a small continuous flow cryostat. No modifications are required for the microscope, and installation is easily accomplished. Using this stage, specimen temperatures below 7.0 K were obtained.

High-Tc Superconductivity of Y-Ba-Cu-O System

A high-Tc superconductivity has been observed in the Y-Ba-Cu-O system by both resistivity and magnetic susceptibility measurements. A superconducting transition with an onset temperature of 120 K has been achieved. About 8% Meissner effect has been confirmed indicating that superconductivity in this material is of the bulk nature. Preliminary X-ray diffraction experiments show that the crystal structure is a non-primitive perovskite structure.