Preparation of Ag-doped NdBa₂Cu₃O_7-δ superconductors by a sol-gel method

Ag-doped NdBa₂Cu₃O_7-δ superconducting ceramics were prepared by a sol-gel method. Ag was distributed uniformly in the sintered samples. The incongruent melting temperature of the NdBa₂Cu₃O_7-δ samples prepared by our sol-gel method was lower than that of the samples prepared by the conventional powder method. The incongruent melting temperature was further decreased by doping with Ag. The authors consider that the incongruent melting is induced by reaction between NdBa₂Cu₃O_7-δ and Ag. The superconducting transition width ΔT(ΔT = T_c(onset) - T_c(end)) was decreased by doping with Ag. The electrical resistivity of a 10 mass% Ag-doped sample dropped sharply from 93 K (T_c(onset)) and showed zero resistivity at 86 K (T_c(end)).