Crystalline characteristics and superconducting properties of Bi2212 thin films by Pechini sol–gel method: effect of heating rate on the film growth

High-quality c-axis epitaxial Bi2Sr2CaCu2O8+δ (Bi2212) superconducting thin films prepared by the Pechini sol–gel method using nitrates as reactants have been grown on SrTiO3(100) single-crystal substrates. The precursor sol was deposited on the substrates via spin-coating method. Through the optimization of experimental parameters, 2.0 K min−1 was found to be the optimal heating rate of pre-sintering stage. Below this heating rate of pre-sintering stage, partial composition segregation occurred in the precursor films that resulted in dispersion of impurity phases in sintered thin films and caused the degradation of superconducting properties. Above this heating rate of pre-sintering stage, the surface morphology of thin films was destroyed, as the macroscopic defects, such as cracks and holes caused by excessive gas emissions during organic matter decomposition process and a sharp increase in roughness of precursor film was observed. Furthermore, through the optimization of heating rate at sintering stage, 3.5–3.0 K min−1 was found to be an optimal heating rate range at which Bi2212 thin films exhibited excellent phase purity and crystalline properties. In optimized growth condition, T c,onset rose to above 95 K. Through the optimization of heating rates of pre-sintering and sintering stages, the excellent Bi2212 superconducting thin films without macroscopic defects were prepared by Pechini sol–gel method using nitrate as reactant.