Effect of nano sized oxalate precursor on the formation of REBa ₂Cu₃O_7-δ (RE= Gd, Sm, Ho) ceramic via coprecipitation method

The formation REBa₂Cu₃O_7-δ (RE= Gd, Sm and Ho) superconducting ceramics from metal oxalate precursors with average grain size less than 50 nm using the coprecipitation method is reported. The metal oxalate powders were heated at 900^oC for 12 hours, pelletized and then sintered at 920°C for 15 hr. The high-T_C phase was observed for all samples as an evidence for the single step transition of (R-T) curves. The T_C(R=0) for samples Gd123, Ho123 and Sm123 were 95 K, 93 K, 91 K, respectively. XRD data showed single phase of an orthorhombic structure for Sm123 and Ho123 samples, small amount of impurities (Gd211) phase were detected for Gd123. SEM micrographs showed large grain sizes that are randomly distributed. These results showed that COP method using nano sized metal oxalates starting powders is very effective to synthesize high quality superconductors and shorten the sintering time required. The formation Gd211 phase for the Gd123 sample might act as a pinning centre explaining the enhancement of the transport properties.