Synthesis of YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf> through different gel routes

High temperature superconducting YBa2Cu3O7 (123) compounds were synthesized through various sol-gel processes using acetate, nitrate-citrate, acetate-citrate and acrylamide gel routes. The gel samples were characterized using IR, electronic and electron spin resonance (ESR) spectroscopy and scanning electron microscopy and the bonding behaviour in the gels was established and correlated to the phase purity of the 123 compound. Heat-treated gel samples were characterized by X-ray diffraction and superconducting properties were evaluated by resistivity and susceptibility measurements. IR, electronic and ESR spectral studies indicated that gels derived from acetate and acetate-citrate routes contained isolated copper acetate groups, whereas homogeneous heterometal ionic networks were observed in gels derived from nitrate-citrate. The ESR spectrum of acrylamide gels suggested homogeneous distribution of the copper(II) ions in the acrylamide polymeric network giving clearly resolved parallel and perpendicular features characteristic of copper(II). The samples derived from the acrylamide gel route are found to yield single-phase 123 compound with sharp resistive and diamagnetic transitions at 90 K, whereas other gel routes yielded multiphase samples with impurities of either BaCuO2 or Y2BaCuO5 phases. © 1995.