Preparation and Characterization of [La, Ln, Ba, Sr, Cel₈ Cu₆O_z (Ln: Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) Ceramics

Abstract

We have prepared ceramic samples of [La_1/6 Ln_1/3 Ba_1/6 Sr_1/6 Ce_1/6] ₈ Cu₆O_z (Ln : Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Y). X-ray diffraction patterns indicated that they were of single phase or nearly single phase except for the samples with Ln = Nd, Sm, Er, Tm and Yb. Their crystal structures were of the (Eu, Ce) ₄ (Eu, Ba)₄ Cu₆ O_z type. The samples only with Ln = Eu, Gd and Dy when annealed in an oxygen atmosphere of P(O₂) = 3 atm exhibited superconductivity with T_c’s in the range of 10-35 K, while the samples with Ln = Eu, Gd, Dy, Ho and Y became superconductors with T_c’s in the range of 5-40 K when annealed at P(C>2) = 200 atm. Additionally, we have prepared nearly single- phase [La_1/6 G_1/3 Ce_1/6 (La_xBa_1-x) _1/3] ₈ Cu₆ O_z (0 ? x ? 0.5) ceramics. The structures of ine samples with x = 0, 0.1 and 0.5 were all tetragonal and those with x = 0.2, 0.3 and 0.4 were orthorhombic according to the x-ray diffraction patterns. The samples with x = 0 and 0.1 exhibited superconductivity having T_c’s in the range of 25–30 K.