Hiroshi Nozaki

Single crystal growth of the superconductor Bi2.0(Bi0.2Sr1.8Ca1.0)Cu2.0O8

Abstract A single crystal of Bi 2.0 ( Bi 0.2 Sr 1.8 Ca 1.0 ) Cu 2.0 O 8 was grown by the floating zone method. This compound melts incongruently and the grown boule is an aggregate of large single crystal grains with growth direction perpendicular to [001]. The crystals tend to grow along the direction [100] and can be easily cleaved along the (001) plane. The grown crystal has orthorhombic symmetry with superstructure and the cell constants a , b and c of the sub-cell are 5.43, 5.43 and 30.63 A, respectively. This crystal reaches zero resistance state at 92 K.

Metallic hole conduction in CuS

Abstract The electrical resistivity, Hall coefficient, magnetoresistance, and magnetic susceptibility of CuS are reported. The compound exhibits excellent metallic conduction among 3d transition metal sulfides. A peculiar temperature dependence of the Hall coefficient is interpreted in terms of two bands of majority holes and minority electrons. The source of the hole carriers is discussed based on Hall effect data and structural considerations. It is concluded that conduction is due to holes in a valence band which is mainly constituted from the 3p orbitals of sulfur. A phase transition close to 55 K is confirmed from the temperature dependence of resistivity and the Hall coefficient.

Preparation and Physical Properties of (PrxY1-x)1+δBa2-δCu3Oy

The Pr-Y solid-solution of the 1-2-3 crystal structure is expressed as (PrxY1-x)1+δBa2-δCu3Oy, with δ ranging from 0 (x=0) to 0.06 (x=1); a small percentage of the Ba sites are occupied by Pr ions. This Pr-Y solid-solution for x>0.5 is nonsuperconducting and does not show metallic conduction. At the metal-semiconductor boundary (x=0.5), the average valence of the Cu ion is smaller by only ca. 0.1 than that of the 90 K superconductor YBa2Cu3O7 (x=0). The relation between the lattice parameters and ionic radii at the Y site is completely different from the empirical relation obtained so far for REBa2Cu3Oy crystals (RE=Y and trivalent lanthanide elements).

Superconductivity in Ba2(1−x)Sr2xYCu3O7−y

We report X-ray and chemical properties, phase transition, magnetic susceptibility and superconducting transition temperature of Ba2(1-x)Sr2xYCu3O7-y. Structural instability was detected for sample with x≥0.6. Phase transition occurs at oxygen number of 6.6. Anomalies in magnetization curves at 4.2 K were detected. The Tc decreases linearly from 92 to 80 K with an increase of x. Strontium and oxygen contents are parameters correlated with the depression of Tc.

Preparation and Physical Properties of PrBa2Cu3Oy

A new compound, PrBa2Cu3Oy, which is isomorphic with YBa2Cu3Oy, was prepared as single phase. With specimens quenched from 920°C, the oxygen content y was 6.8 ± 0.1 and the ratio of Pr3+ to Pr4+ was 0.4:0.6. With furnace-cooled specimens, the value of y was 7.1 ± 0.1 and the ratio became 0.1:0.9. The average valence of Cu ions was 2.0 ± 0.1 for the former and 2.1 ± 0.1 for the latter. Specimens handled both ways were nonmetallic and nonsuperconducting down to 4.2 K.

Preparation of a new type BaCu2S2

Abstract A new type of BaCu 2 S 2 has been prepared through the sulphurization of a mixture of BaCO 3 and CuO. The X-ray powder diffraction pattern of the sulphide was indexed on the basis of tetragonal cell with the lattice parameters of a = 3.909(6) and c = 12.655(2)A.

Synthesis, structure, and electronic properties of Cu2SiQ3 (Q=S, Se)

Cu2SiS3 was prepared by the reaction of the constituent binary chalcogenides and elements at 800°C, and the isotypic selenium compound was synthesized by using a KCl/LiCl flux at 550°C. Their crystal structures were determined from single-crystal X-ray data (Cu2SiS3: a=6.332(1), b=11.230(1), c=6.273(1) A, β=107.49(1)°, Z=4, R=0.0319 for 2383 reflections and 54 variables. Cu2SiSe3: a=6.669(1), b=11.797(1), c=6.633(1) A, β=107.67(1)°, Z=4, R=0.0279 for 1976 reflections and 54 variables). The crystal structure may be described as a monoclinic superstructure of sphalerite type, in which sulfur atoms form a slightly distorted cubic close-packed sublattice, and the Cu and Si atoms are located at one-half of the available tetrahedral voids between the S-layers. The DSC measurement indicated the incongruent decomposition of Cu2SiSe3 at 632.2°C, and the electrical resistivity measurements confirmed the expected semiconducting behaviour of both compounds.

Phase transition in Bi-based superconductive oxides examined by HRTEM

Abstract A Bi-Sr-Ca-Cu-O oxide rapidly cooled from 900°C, at which temperature the specimen is partially molten, consists of a major component of the (2201)-phase and a minor component of the impurity phases. (Ca1−zSrz)3Cu5Oy (z=0.46) and (Ca1−x, Srz)2CuO3 (z=0.09). The grains of both phases have a columnar shape. High-resolution transmission electron microscopy (HRTEM) shows that thin plates of the (2201)-phase are irregularly mixed with the grains of the impurity phase. For the specimen annealed at 500°C in air the electrical resistivity abruptly decreases at the superconducting transition temperature Tc of about 75 K, and this is related to the appearance of a small amount of the (2212)-phase. A characteristic structure found in local areas suggests that a transition state exists between the (2201)-phase and the (2212)-phase. When the specimen is annealed at 850°C the (2212)-phase becomes the major component, and Tc is increased to 87 K. When further annealed at 880°C, the (2223)-phase becomes the major component, and this seems to be initiated by the disproportionation reaction of the (2212)-phase. The resistivity starts to drop at about 112 K.

Preparation and Properties of Ba2YCu3O7-y Single Crystals Grown Using an Indium Oxide Flux

Single crystals of Ba2YCu3O7-y were prepared using an In2O3 flux. Considerable variations in 7-y exist among crystals from different batches, although the same annealing conditions were applied. Tetragonal phases were found to be quenchable at 630°C in air for certain single crystals, although tetragonal phases of highly aluminous sintered specimens were unquenchable below 700°C. These characteristics are explained by the variation of oxygen mobility among the single crystals which were controlled by aluminium impurities and certain defect structures.

Superconductivity of the system Nd1+2xBa2(1−x)Cu3Oy (0≤x≤0.4): effect of the magnetic Nd3+ ion occupying the Ba-site

A solid solution system Nd1+2xBa2(1-x)Cu3Oy (0≤x≤0.4) was investigated through its magnetic susceptibility and electrical resistivity. In the system, trivalent Nd ions partly occupy the Ba2+ sites of the structure, depending on x. Superconductivity was observed in the range of x=0~0.16 and the transition temperature decreased steadily with increasing x. The resistivity in a normal state varied from metallic to semiconductive in character with an increment of x. These phenomena are discussed from the viewpoint of how trivalent, magnetic Nd ions in the Ba-O layers affect superconductivity in the system.