Effect of pH on the synthesis of YBa<inf>2</inf>Cu3O7 by the sol-gel process

The high-temperature superconducting compound YBa2Cu3O7 (123) was synthesized through the sol-gel process using metal acetates as the starting materials. The gel samples were prepared by varying the initial pH of the aqueous solutions from 6.0 to 8.0, and their structural properties were identified using infrared (IR) spectroscopy. The 123 compounds that resulted from these gels were characterized by X-ray diffraction (XRD), scanning electron microscopy, and resistivity and susceptibility measurements. The IR spectra indicated that the gels prepared from pH 6.0 solutions did not contain any free metal acetate, while those obtained using other pH values contained individual acetates of either copper, barium or yttrium. XRD data revealed that phase-pure 123 compound was formed only from the sample prepared at pH 6.0; all other pH solutions yielded Y2BaCuO5 (211) as an impurity phase along with the 123 compound. This could be due to the homogeneous distribution of the metal ions in the gel prepared at pH 6.0, as evidenced by its IR spectrum. Resistivity and susceptibility measurements showed that all samples exhibited a superconducting transition (Tc) at 90 K, except the sample prepared at pH 7.0, which showed a Tc of 79 K. © 1994.