SYNTHESIS OF YBA2CU3O7 THROUGH DIFFERENT GEL ROUTES

High temperature superconducting YBa2Cu3O7 (123) compounds were synthe sized through various sol-gel processes using acetate, nitrate-citrate , acetate-citrate and acrylamide gel routes. The gel samples were char acterized using IR, electronic and electron spin resonance (ESR) spect roscopy 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 diffra ction 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 co ntained isolated copper acetate groups, whereas homogeneous heterometa l ionic networks were observed in gels derived from nitrate-citrate. T he ESR spectrum of acrylamide gels suggested homogeneous distribution of the copper(II) ions in the acrylamide polymeric network giving clea rly resolved parallel and perpendicular features characteristic of cop per(II). The samples derived from the acrylamide gel route are found t o yield single-phase 123 compound with sharp resistive and diamagnetic transitions at 90 K, whereas other gel routes yielded multiphase samp les with impurities of either BaCuO2 or Y2BaCuO5 phases.