Melt processing of Bi-2212 thick films and bulk components

Critical current densities of melt processed Bi-2212 on Ag-substrates are remarkably depending on the thickness in the range from 1000 mu m to 10 mu m. They increase from several 10(3) A/cm(2) to 10(4) with decreasing thickness. The most obvious microstructural feature in thin samples with high critical current densities is the pronounced alignment of the platelet like grains with their c-axis perpendicular to the substrate. This texture gets lost with increasing sample thickness. Fora fixed sample thickness, the melting temperature determines the amount of liquid and solid (second) phases in equilibrium. At the optimum melting temperature just enough liquid is formed to densify the sample without coarsening of the second phases which otherwise lead to inhomogeneous microstructures in the final product and suppressed critical current densities. There exists an optimum melting temperature window of +/-2 degrees C for thin and +/-8 degrees C for thick samples. Processing below this windows leads to porous microstructures, processing above produces coarse secondary phases, Bi-loss and loss of liquid. These conditions lead to suppressed critical current densities. Silver additions lower the solidus temperature of Bi-2212 as much as 25 degrees C and improve the critical current density in thicker components processed under oxygen. Reduced oxygen partial pressures (e.g. 0.21 atm) lower the solidus temperature of Bi-2212 also, but lead to an increased frequency of amorphous grain boundary layers and, therefore, much lower critical current densities compared to samples processed in oxygen (pO(2)=1 atm).