Identification of the Superconducting Phase in the Bi-Ca-Sr-Cu-O SystemE. Takayama‐Muromachi, Yoshishige Uchida, Akira Ono et al.|Japanese Journal of Applied Physics|1988 In order to identify the superconducting phase in the Bi-Ca-Sr-Cu-O system, phase search experiments were performed. The results of power X-ray study, EPMA study, specific gravity measurements and oxygen analysis revealed that the compound having the composition Bi 2 (Ca, Sr) 3 Cu 2 O 9 or Bi 2 (Ca, Sr) 3- Δ x Cu 2 O 9- Δ y is responsible for the high- T c superconductivity. Two possible structure models, which are closely related to the structure of the bismuth titanate Bi 4 Ti 3 O 12 , are proposed for this compound.
High T<sub>c</sub> Superconductor YBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub>–Oxygen Content vs T<sub>c</sub> Relation–E. Takayama‐Muromachi, Yoshishige Uchida, Motohiko Ishii et al.|Japanese Journal of Applied Physics|1987 High T c superconductor YBa 2 Cu 3 O y , having various oxygen contents have been examined by a.c. susceptibility, d.c. conductivity and Raman spectrum measurements. The T c is greatly affected by the oxygen content, being lowered by decreasing oxygen content. Particularly, the T c drops markedly when the compound takes a tetragonal form. To confirm the y vs temperature relation, the compound was reexamined by thermogravimetry. The new results cast doubt on our previous y value (6.5> y >5.8).
On the 110 K Superconductor in the Bi-Ca-Sr-Cu-O SystemE. Takayama‐Muromachi, Yoshishige Uchida, Yoshio Matsui et al.|Japanese Journal of Applied Physics|1988 We found a new compound in the Bi-Ca-Sr-Cu-O system which has a different structure from the 80 K superconductor Bi 2 (Ca, Sr) 3 Cu 2 O y . The c -dimension of this compound is ∼37 Å and is ∼6 Å longer than that of Bi 2 (Ca, Sr) 3 Cu 2 O y . Although we have not obtained a single-phased sample yet, the clear correlation between the diamagnetic susceptibility just below 110 K and the content of this compound included in the sample strongly suggests that the compound with c ≈37 Å is responsible for the superconductivity of T c ∼110 K.
Superconductivity of YBa<sub>2</sub>Cu<sub>3-x</sub>M<sub>x</sub>O<sub>y</sub> (M = Co, Fe, Ni, Zn)E. Takayama‐Muromachi, Yoshishige Uchida, K. Kato|Japanese Journal of Applied Physics|1987 The superconductivity of YBa 2 Cu 3- x M x O y , (M = Co, Fe, Ni, Zn; x = 0.1-0.4) was examined by means of ac susceptibility measurements. The results indicated that Cu in the Cu2 site (between the Y and the BaO layer) plays a more substantial role in superconductivity than that in the Cu1 site (between the BaO layers). Combining this with our earlier results for the La 1+ x Ba 2- x Cu 3 O y system, we suggest that holes doped mainly in the O 2 p orbitals of the rock-salt-type BaO layers form Cooper pairs through some medium (spin fluctuations or possibly other collective modes) excited in the Cu2 layer.
Die Kristallstruktur von YbFe<sub>2</sub>O<sub>4</sub>K. Kato, I. Kawada, Noboru Kimizuka et al.|Zeitschrift für Kristallographie|1975 The crystal structure of YbFe 2 O 4 was determined and refined by the x-ray method. This compound crystallizes trigonal in the space group R [unk] m with the unit-cell dimensions a = 3.455 ± 0.001, c = 25.054 ± 0.010 Å. The unit cell contains three formula units. The structure consists of the alternating layers of YbO 3/2 and Fe 2+ Fe 3+ O 5/2 . The oxygen ions are arranged like a sort of closest packing of spheres. The Yb ion is surrounded by six oxygen ions octahedrally, the Fe ion by five oxygen ions forming a trigonal bipyramid. This structure presents a new structure type for the AB 2 X 4 compound.