Efficient High‐Temperature Annealing Effect on the La _1.84 Sr _0.16 CuO ₄ Superconducting Ceramics Prepared by Spark Plasma Sintering

To explore the possibility of improving the critical current density ( J c ) of polycrystalline La 1.84 Sr 0.16 CuO 4 (LSCO) superconducting ceramics, high‐density LSCO samples were prepared by means of spark plasma sintering (SPS) and the influence of a high‐temperature postannealing treatment (1000°C–1300°C) on these high‐density LSCO ceramics was systematically investigated. In spite of a partial surface decomposition of the LSCO pellets and changes in the ceramic density, the high‐temperature annealing significantly improved the sharpness of the superconducting phase transition and the critical temperature. The magnetic critical current density, determined from magnetization loops using the Bean model and the full sample dimensions, was markedly enhanced. After annealing at 1300°C, the maximum J c of the LSCO ceramic calculated from magnetization measurements reached nearly 60 000 A/cm 2 , which compares well to previously published values reported for LSCO single crystals with the magnetic field applied parallel to the Cu–O planes. However, granularity effects were revealed using AC‐susceptibility and Hall probe microscopy. Our investigation demonstrates that a specific postannealing treatment following SPS processing provides an effective route to achieve high critical current densities in polycrystalline high‐temperature cuprate superconductors.