Hideo Tanigawa

Preparation of fibrous Bi(Pb)-Sr-Ca-Cu-O crystals and their superconducting properties in a bending state

The superconducting fibrous crystals of Bi(Pb)-Sr-Ca-Cu-O (2212 phase) have been prepared by heating a glassy melt-quenched plate in an oxygen atmosphere. The crystals show Tc(onset) at 75 K and Tc(end) at 70 K. The fibers have a single crystal nature and can be bent to a radius of curvature (R) of 0.4 mm without a decrease in the Tc value. The highest Jc is 67000 A/cm2 (63 K, zero magnetic field) in a nonbending state. It surpasses 35000 A/cm2 even in a bending state of R>1 mm and finally decreases down to 3200 A/cm2 for R=0.4 mm.

Growth of Bi-Sr-Ca-Cu-O based superconducting whiskers

Abstract Superconducting whiskers of the Bi system have been grown by heating a glassy melt-quenched plate in a stream of O 2 gas. We have examined the growing phase and superconductivity of the whiskers grown at the different heating and cooling conditions. The Bi 2 Sr 2 CaCu 2 O 8 (2212 phase) whiskers are grown from a wide range of initial compositions when the melt-quenched plates are heated at 840°C. The Bi 2 Sr 2 CuO 6 (2201) phase is dominant in the whiskers grown at lower temperature, 820 and 810°C. The growing pure 2223 whiskers have not been obtained so far. For the superconductivity of the 2212 whiskers, high oxygen partial pressure ( P O2 , rapid cooling and higher heating temperature are preferable. Low P O2 and slow cooling are preferable for the 2223 phase contained in the 2212 whiskers as a minor part. Heating time does not give remarkable effects on the growing phase and superconductivity.

Growth of Li-doped and dopant-free Bi-Sr-Ca-Cu-O superconducting whiskers

Abstract The effects of dopant, Li, Na, K, Ga, Ge, Sb and Te, on the growing conditions and superconductivity in Bi-Sr-Ca-Cu-O whiskers have been examined and compared with dopant-free whiskers, synthesized by heating a glassy melt-quenched plate in a stream of O 2 gas. Every whisker has the 2212 structure as its main phase and a small amount of the 2223 phase, so that two resistance drops are observed in the R-T curve. Only Li is effective for increasing the T c of both the 2212 and the 2223 phase, and the T c s are enhanced with increasing Li content in the whiskers. The onset temperatures of Li-doped whiskers for the 2212 and 2223 phases are higher than those of the other samples by about 10 K and 6 K respectively. The T c,zero has a good correlation with the lattice parameter c of the 2212 phase. The length of the c -axis of the Li-doped sample is about 0.1 A longer than that of the other samples. A T c,zero value of 107 K is obtained and a T c,zero of 112 K is indicated for the 2223 phase by extrapolation of the R-T curve in the Li-doped whiskers. A J c of 34 000 A/cm 2 at 77 K and 300 000 A/cm 2 at 66 K in a zero magnetic field have been obtained for the Li-doped whisker. The J c decreases steeply in magnetic field above 0.2 T at 77 K, and an anisotropy of the J c value of samples in a magnetic field has been observed.

Preparation and critical current density of Bi2Sr2Ca2Cu3O10+x superconducting whiskers

The whiskers of the Bi2Sr2Ca2Cu3O10(2223) phase have been prepared by heating the Bi2Sr2CaCu2O8(2212) whiskers inside of a calcined Bi2Sr2Ca4Cu6Pb0.5Ox powder. Temperature and magnetic field dependence of the critical current density (Jc) have been measured. The whisker yields a maximum Jc of 7.3×104 A/cm2 at 77 K, and higher than 1×104 A/cm2 below 96 K in zero applied field. At 77 K the 2223 whisker shows Jc values above 1×104 A/cm2 up to 1 T, in contrast to the 2212 whisker (1×102 A/cm2, B=1 T) which shows the steep decrease of Jc in magnetic field above 0.2 T.

Flexible superconducting whiskers of the Li‐doped Bi‐Sr‐Ca‐Cu oxide

Flexible Li‐doped Bi‐Sr‐Ca‐Cu‐O superconducting whiskers have been prepared by heating a glassy melt‐quenched plate in a stream of O2 gas. The whiskers show a resistance drop at 110 K with a zero resistance at 81 K. These values are higher than those of the Pb‐doped Bi‐Sr‐Ca‐Cu‐O whiskers by 5 and 11 K, respectively. The doping of Li is effective to raise Tc for both the 2212 phase and the 2223 phase. The Jc values of the Li‐doped whiskers are 30 000 A/cm2 at 77 K and 300 000 A/cm2 at 66 K in a zero magnetic field.

Superconducting whiskers and crystals of the high Tc Bi2Sr2Ca2Cu3O10 phase

Whiskers of the high Tc Bi2Sr2Ca2Cu3O10  (2223) phase have been prepared by annealing Bi2Sr2CaCu2O8  (2212) whiskers in a Bi2Sr2Ca4Cu6Pb0. 5Ox powder. By the same method, single‐crystal sheets of the 2212 phase have also been converted to the 2223 phase, resulting in 2223 sheet crystals as large as approximately 1 mm2. Although the original sample outlines are retained after the phase conversion, the smooth surfaces were lost due to contact with the powder during annealing. A zero‐resistance temperature of 107 K and a maximum Jc value of 7.3×104 A/cm2 at 77 K in a zero magnetic field were obtained for the 2223 whisker.

Preparation of the Bi(Pb)-Sr-Ca-Cu-O fibrous crystals containing the high-Tc phase

Fibrous crystals containing the high-Tc phase of the Bi(Pb)-Sr-Ca-Cu-O superconductor have been prepared by heating a melt-quenched plate in a stream of O2 gas. The fibers show a remarkable resistance drop at 105 K. The high-Tc phase is detected on a microarea X-ray diffractometer and the high-Tc crystals are found to be stacked between the low-Tc platelike crystals. The highest Tc(zero) value so far obtained is 96 K.

Modified Zone-plate Interferometer for Testing Aspheric Surfaces

A new type of common path interferometer using a modified zone-plate developed for testing aspheric surfaces is described. The modified zone-plate is made by combining two kinds of zone-plates; the semicricular part of the plate produces the spherical wave, and the remainder the desired aspheric wave. These are synthesized by digital computation. A method of computation for synthesizing the modified zone-plate and some experimental results of the test of parabolic mirrors are given.

Effects of Sulfur Addition on the Superconductivity of Y–Ba–Cu–O Compound

Sulfur added Y-Ba-Cu-O compounds with a nominal composition YBa2Cu3OxSy were prepared by two methods; a) using CuS or Cu2S instead of CuO, b) annealing the YBa2Cu3Ox in H2S atmosphere. By the method a), sulfur atoms were not incorporated into the crystal lattice of the 1:2:3 phase and made it multiphasic. Although Tc was lowered with increasing sulfur content, Jc for y=0.03 was about twice as high as that for y=0.00. In the case of the method b), sulfur atoms could be incorporated into the crystal lattice of 1:2:3 phase when the compound was annealed at temperatures up to 200°C. The sulfur-incorporated compounds showed semiconductive behavior.

Preparation and Properties of the High-Tc Bi2Sr2Ca2Cu3O10 Whiskers and Crystals

Whiskers of the high-Tc Bi7Sr2Ca2Cu3O10 (2223) phase have been prepared by annealing Bi2Sr2CaCu2O8 (2212) whiskers in a Bi2Sr2Ca4Cu6Pb0.5Ox powder. By the same method, single crystals of the 2212 phase have also been converted to the 2223 phase, resulting in 2223 sheet crystals as large as approximately 1mm2. In the case of the Bi2Sr2CuOx (2201) single crystals as a starting material, the 2223 phase has been partially formed after annealing in the powder, because the rate of the phase conversion is slower than that for the 2212 phase. A zero-resistance temperature of 107K and a maximum Jc value of 7.3×10 4A/cm2 at 77K in a zero magnetic field were obained for the 2223 whisker. The 2223 whisker shows Jc values above 1×104A/cm2 up to 1T at 77K.