Synthesis of Ca-doped Y124 Superconductor by Polymerized Complex Method Followed by O₂-HIP Technique and Discussion of Ca-site Selectivity in the Crystal Structure

Abstract

We report Ca-site selectivity in the crystal structure of Y124(YBa₂Cu₄O₈) superconductor. We sucsessfully synthesized superconducting samples with nominal compositions of (Y_1-xCa_x)Ba₂Cu₄O₈ (series-A: x=0.0, 0.05, 0.1) and Y(Ba_2-yCa_y)Cu₄O₈ (series-B: y=0.0, 0.05, 0.1) by polymerized complex method followed by 0₂-IIIP technique. Neutron powder diffraction measurement has shown excess impurities in pmpotion to Ca-content in series-B. An extension of Δ T_c(10-90%) was also observed in series-B by AC-magnetic susceptibility measurement. It is suggested that the formation of these impurities in series-B originate from a discrepancy in ideal composion, that is, (Y_1-xCa_x)Ba₂Cu₄0₈ (seires-A). We conclude that Ca-atom preferentially substitutes Y-atom in the 124 structure for these reasons.