Preform optimization in infiltration growth process: An efficient method to improve the superconducting properties of YBa2Cu3O7−δ

The effect of compaction pressure applied to the Y2BaCuO5 (Y-211) preform during its fabrication, on the final microstructures and current densities (Jc) is investigated. The necessity for optimizing the sintering conditions in order to provide mechanical stability to the preform prior to the infiltration of liquid phases is demonstrated. The sample fabricated under optimized conditions showed Jc values better than 103 A cm−2 up to applied magnetic fields of 6.5 Tesla at 77 K. The microstructural factors influencing the field dependence of Jc 'Jc(H)' at low and high fields are investigated. Extensive nano-twinning with large number of crossing twins observed in the optimized sample and the associated high defect densities are correlated to be the source of flux pinning to high fields. The fact that YBa2Cu3O7−δ (YBCO, Y-123) superconductor obtained employing the present Preform Optimized Infiltration and Growth Process (POIGP) yields a homogenous and dense distribution of fine Y-211 particles, that creates suitable twin/defect densities to provide flux pinning at high fields, is of technical importance.