The Sintering Effect on the Phase Formation and Transport Current Properties of SmBa2Cu3O7−δ Ceramic Prepared from Nano-Coprecipitated Precursors

Abstract

High-temperature superconducting ceramic with the formula SmBa2Cu3O7−δ was prepared from metal oxalate precursors with an average grain size < 35 nm using the coprecipitation method. The metal oxalate powders were heated at 900 °C for 12 h, where they were pelletized and then sintered at different temperatures (920, 930, 940, and 950 °C) for 15 h. All sintered samples exhibited a metallic behavior with zero-resistance transition temperatures, T C(R = 0), of 92.8, 92.5, 89.5, and 84.0 K when the samples sintered from 920–950 °C, respectively. The critical current density (J C) decreased as the sintering temperature increased due to the formation of non-superconducting phases or insulator that enhanced the weak-link effect. X-ray diffraction (XRD) data showed the formation of impurity phases (Sm-211 and Sm210) at 930 and 940 °C, respectively. The crystalline size remains unchanged for all samples, and the best results were obtained for the sample sintered at 920 °C, where the single phase of an orthorhombic structure was detected and the highest T C was recorded. Scanning electron microscope (SEM) micrographs showed large grain sizes that were randomly distributed; the number of gaps between the grains increased as the sintering temperature increased due to the decomposition mechanism that enhanced the weak links between the grains and suppressed the transport current properties. The obtained results proved that high-quality Sm123 superconductor with minimum or no impurities can be produced when the sintering was applied at 920 °C for 12 h. This sintering temperature is sufficient to convert the nano-sized metal oxalates as a starting precursor to pure and high-quality polycrystalline SmBa2Cu3O7−δ . These results are important to simplify the preparation of SmBa2Cu3O7−δ at a lower temperature for HTSC device applications.