Synthesis of ultrafine Y₂BaCuO₅ powder and its incorporation into YBCO bulk by powder melting process

A solid state sintering process for the synthesis of ultrafine Y₂BaCuO₅ precursor has been developed and YBCO bulk samples containing Y₂BaCuO₅ particles less than 500 nm in diameter have been prepared successfully by powder melting process (PMP). The solid state sintering process consists of two steps: firstly, BaCuO₂ powder was synthesized by calcining the mixture of BaCO₃ and CuO powders; secondly, BaCuO₂ powder was well mixed with commercial Y₂O₃ in a molar ratio of 1:1, and sintered at 900°C for 14 h in flowing oxygen. After ball milling, ultrafine Y₂BaCuO₅ powder with an average diameter below 0.5 μm was produced. This kind of ultrafine Y₂BaCuO₅ powder was used as precursor and quasi-single crystal YBCO samples with a nominal composition of YBa₂Cu₃O_6+δ+15 wt.% excess Y₂BaCuO₅+0.5 wt.% CeO₂ were prepared by PMP. Y₂BaCuO₅ particles less than 500 nm in diameter were found within textured YBCO matrix. A high density of twins with an average spacing of about 60-80 nm was also observed. Magnetization measurements have been performed on the sample and critical current densities (J_c) have been calculated based on the extended Bean critical state model. The sample exhibits J_c values of 4.57×10⁶ and 1.85×10⁵ A/cm² in 1 T magnetic field at 20 and 77 K, respectively. Such high J_c values are attributed to the fine 211 particles and related defects.