Superconducting properties and non-isothermal crystallization kinetics of a Bi2Sr2CaCu2O8+δ (Bi2212) superconductor prepared by the Pechini sol–gel method

Abstract

Bi2212 superconductors with crystallization treatments at different temperatures were prepared by the Pechini sol–gel method, and their structural, thermal and transport properties were investigated. The X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) results revealed the high purity and sheet crystal structures of the prepared samples. The non-isothermal crystallization kinetics and process of the Bi2212 superconductor were characterized and analyzed by differential scanning calorimetry (DSC) and Jeziorny and Mo methods, respectively. The results showed that both the Jeziorny and Mo methods were well suitable for describing the non-isothermal crystallization process of the Bi2212 superconductor prepared by the Pechini sol–gel method. The Avrami exponent (n = 2) confirmed the two-dimensional sheet growth mechanism of the Bi2212 superconductor. In addition, the non-isothermal crystallization kinetic parameter Z_c increased with the increase in cooling rate. The crystallization parameter F(T) also increased with the increase in crystallinity, and the F(T) values were calculated to be 4.79 and 42.66 when the crystallinity values were 20% and 90%, respectively, indicating that for the Bi2212 superconductor, it was harder to crystallize at relatively larger crystallinity. Furthermore, the transport properties of the samples were greatly improved after the cooling crystallization process. Sample J3 had the highest onset of the superconducting transition T_(c,onset) of 80.1 K, which was higher than the 73.1 K value determined for sample J0. Also, sample J2 had the best zero resistivity superconducting transition temperature T_(c,zero) value of 70.1 K, which was higher than the value of 63.2 K for sample J0. The maximum calculated J_c value was 7.62 × 10⁴ A cm⁻² at 2 K for sample J2, which was higher than the 4.70 × 10⁴ A cm⁻² value determined for J0.