On the roles of HEC in Pechini sol-gel method: Enhancement of stability, wettability of the sol and surface roughness of Bi2212 film

Bi2212 superconducting thin film was prepared through a modified Pechini sol-gel method called surfactant assisted Pechini. Nitrates were used as reactors, ethylenediamine tetraacetic acid (EDTA) and hydroxyethyl cellulose (HEC) was adopted as chelating agent and surfactant respectively to prepare sol for Bi2212 film. The effects of HEC on the phase formation, crystallization behavior, morphology and superconductivity of the samples were characterized using X-ray diffraction, field emission scanning electron microscope, atomic force microscope and the standard four-probe method. C-axis epitaxial Bi2212 thin film with high Bi2212 phase purity was obtained through the modified method, and the sample had good crystallization properties, smooth surface and excellent electrical transport properties. Furthermore, a model is proposed to clarify the roles of surfactant in the preparation of Bi2212 films.