MICROSTRUCTURE AND SUPERCONDUCTING PROPERTIES OF ATTRITION-MILLED BI2SR2CACU2OX

The microstructure and superconducting properties of Bi2Sr2CaCu2Ox (Bi -2212) during high-energy attrition milling were investigated in detai l by a combination of x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and magnetization techniques. The s tarting superconducting powder was milled in a standard laboratory att ritor using yttria-stabilized ZrO2 balls and a stainless steel tank. A fter selected time increments, the milling was interrupted and a small quantity of milled powder was removed for further analysis. It was fo und that the deformation process rapidly refines Bi-2212 into nanomete r-size crystallites, increases atomic-level strains, and changes the p late-like morphology of Bi-2212 to granular submicron clusters. At sho rt milling times, the deformation seems localized at weakly linked Bi- O double layers, leading to twist/cleavage fractures along the {001} p lanes. The Bi-2212 phase decomposes into several bismuth-based oxides and an amorphous phase after excessive deformation. The superconductin g transition is depressed by about 10 K in the early stages of milling and completely vanishes upon prolonged deformation. A deformation mec hanism is proposed and correlated with the evolution of superconductin g properties. The practical implications of these results are presente d and discussed.