In the present work, the effect of different annealing-time on the properties of Bi2Sr2Ca1Cu1.75Na0.25Oy (Bi-2212) superconducting compound is presented. First, the samples were produced by hot-pressing method under 33 MPa pressure at 750 °C in accordance with previous works. After annealing, the samples were kept at 840 °C for 15, 30 and 60 h, respectively, for postannealing process. XRD results demonstrate the formation of Bi-2212 phase in large amount in all samples. SEM images show the formation of different grain morphologies depending on the postannealing time. The sample postannealed for 60 h at 840 °C has the highest superconducting transition temperature (Tc, onset), 91 K, obtained from M–T measurements. The magnetic properties of samples have been investigated using M–H hysteresis loops at 15 K in the range − 1.6 × 106 to + 1.6 106 A/m. The widest M–H curves were obtained in the postannealed sample for 60 h at 840 °C, probably as a result of both the improvement of crystallinity, cleaner grain boundaries and better grain orientation. In addition, the widest hysteresis curve observed in that sample in the entire applied magnetic field range is an indication that it has strong pinning behavior. The critical current density (Jc) was investigated via Bean’s model from these data. Finally, the sample postannealed at 840 °C for 60 h reached a Jc value of 2.903 × 106 A/cm2 at H = 1.9 T and T = 15 K, which is, approximately, 44% higher than the determined in annealed samples (2.015 × 106 A/cm2).

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