Abstract
Superconducting Y1-xCaxBa2Cu4Oy ceramics with x=0, 0.05 and 0.1 have been synthesized by the polymerized complex method, which includes three important major steps: (1) formation of metalcitrate complexes dispersed into ethyleneglycol and water, (2) fabrication of polymerized complexes formed through esterification between ethyleneglycol and metal-citrate complexes and (3) pyrolysis of the polymerized complex precursor. The main advantages of the present technique are the elimination of centrifugation, ageing and fine control of pH usually required for other solution techniques. Complex magnetic susceptibility measurements for YBa2Cu4Oy (Y124) prepared under one atmospheric oxygen pressure have revealed a progress in homogeneity and superconducting properties compared to those of samples prepared by the other techniques. Better superconducting properties have been achieved for the parent Y124 when the sample was additionally treated with a high oxygen pressure (post O2-HIP). The post O2-HIP treatment is probably essential for producing Ca-doped Y124 in its pure form. Tc is increased from 81.3K for x=0.0 to 86.7K for x=0.05.However, further increase in Ca content results in partial decomposition of the sample into Y124, Y247 and other unknown impurities under the present HIP condition. The increase in Tc with increasing Ca content would be attributable to an inrease in hole concentration owing to the substitution of the divalent Ca ion for the trivalent Y ion.
