Syunichiro Kawashima

A new tupe of crystal structure in the Pb-Pr-Sr-Cu-O system

Abstract A classification of p-type superconductors is proposed. According to this classification, PbPr 2.4 Sr 1.6 Cu 2.6 O y ceramic was designed and synthesized as a ceramic having a new crystal structure. This ceramic has a tetragonal symmetry ( a =0.388 nm, c =2.914 nm) and consists of three blocks which are a (Pb/Cu)-O single layer, a Cu-O 5 pyramid and a fluorite-type Pr 2 -O 2 layer. It is expected to be a mother material of superconductors.

Dielectric Ceramics for Microwave Application

A review has been made to find the technical trend on the presently developed dielectric ceramics for microwave applications. Some new dielectric ceramics recently developed by authers that is (1) temperature stable and high Q materials of Ba(Zn1/3Ta2/3)O3 (BZT) and Ba(Zn1/3Nb2/3)O3–Ba(Zn1/3Ta2/3)O3 (BZNT) ceramics and (2) temperature stable and high dielectric constant materials of BaO–Sm2O3–TiO2(BST) ceramics and their applications have been introduced.

Superconductivity in a Ln-Pb-Sr-Ca-Cu-O System

The superconductivity and crystal structure of a Ln-Pb-Sr-Ca-Cu-O system, where Ln=Y or lanthanide, have been studied. The maximum onset temperature and zero resistance obtained for a nominal composition of YbPbSr2Ca2Cu3Ox were 78 K and 64 K, respectively. This ceramic is composed of a new phase which has a tetragonal symmetry with a=3.81 A and c=15.7 A, and a second phase, Yb2SrO4.

Superconductivity Near 50 K in a Bi–La–Ca–Cu–O System

A new oxide superconductor has been found in the Bi-La-Ca-Cu-O system. The maximum onset temperature and zero resistance temperature were 52 K and 21 K, respectively, obtained for a nominal composition of Bi2La0.5Ca3.5Cu3Ox ceramics sintered at 830°C for 110 h in air. The powder X-ray diffraction patterns of this ceramic were well indexed by a tetragonal symmetry with a=0.54 nm and c=2.98 nm, which is similar to that of Bi2Sr2CaCu2Ox ceramics.

Superconducting Properties in a Bi–Sr–Ca–Cu–O System

Superconducting properties in a Bi-Sr-Ca-Cu-O system have been studied. Two types of superconductors were observed: one has a transition temperature of 80 K, and the other has two transitions at 80 K and 110 K. XRD measurements suggest that the latter superconductor has at least two phases. The phase which seemed to be responsible for the superconductivity above 80 K was investigated by means of XRD, SEM and XMA.

Annealing Effect of High-Tc Superconducting Y(Ba1-xSrx)2Cu3O7-y Ceramics

Annealing effect of high-Tc superconducting Y(Ba1-xSrx)2Cu3O7-y [x=0, 0.1, 0.2] ceramics on the superconducting transition temperature and lattice constants has been studied. For well annealed Y(Ba0.8Sr0.2)2Cu3O7-y ceramics, the superconducting transition onset temperature was 95 K and the offset temperature was 92 K. These transition temperatures are comparable to those of the YBa2Cu3O7-y ceramics.

Synthesis of Bi–Sr–Ca–Cu–O Ceramics with Large Intergrowth Defects

Superconducting Bi-Sr-Ca-Cu-O ceramics with intergrowth defects larger than 1.8 nm in half of the c-axis length were synthesized at a nominal composition of Bi2Sr2Ca4Cu6.5Oy. Electrical resistance and a.c. susceptibility for the ceramics were measured. No indication of a Tc higher than 110 K was obtained.

Synthesis and Characterization of Single-Phase (Tl1-xBix)Sr2Ca2Cu3Oy Ceramics

The synthesis and characterization of the “1223” phase in a Tl-(Bi)-Sr-Ca-Cu-O system are described. Almost-single-phase (Tl1-xBix)Sr2Ca2Cu3Oy ceramics (x≦0.25) were obtained by using Tl2O3 and Tl2O as Tl sources. The zero-resistance temperature of the so-called “1223” phase reached 115 K for the nominal composition of Tl2Bi0.25Sr2Ca2Cu3Oy ceramic. The Bi addition stabilized the “1223” phase and improved the superconductivity.

Superconductivity in a Tl-Pb-Pr-Sr-Cu-O System

Superconductivity in the Tl-Pb-Ln-Sr-Cu-O (Ln=La, Pr, Nd) system has been found. Samples were synthesized by annealing of precursors, Pb-Ln-Sr-Cu-O ceramics, in Tl oxide vapor. In the case of Ln=Pr, electrical resistance vanished below 43 K, and the Meissner effect appeared below 46 K.

Formation and Decomposition of Superconducting BiSrCaCu2Ox Ceramics

Phase changes of superconducting BiSrCaCu2Ox ceramics against temperature and atmosphere have been studied. Phases of high-Tc superconducting BiSrCaCu2Ox ceramics sintered at 850°C in air were decomposed by low-temperature annealing, therefore the phases are not stable at low temperatures. The formation of these phases depended on the sintering atmosphere.