Microstructure development of partially-melted Bi-2212

Abstract

Sintered Bi₂Sr₂CaCu₂O₈ (Bi-2212) powder was partially-melted in air at 887°C with a soak of 30 minutes. The resulting microstructure as a function of the cooling rate was analyzed through scanning electron microscopy. At slower cooling rates of 10°C/h and 20°C/h, the Bi-2212 is single phase, homogenous, and composed of platelet type grains with nearly equilibriated growth. Grain diameter varies from a maximum diameter of 10 μm and thickness of 0.6 μm to 2 μm with thickness less than 0.1 μm. The alignment of the platelet grains is influenced by the cooling ratefrom the partial-melt temperature where the slowest cooling rate of 10°C/h resulted in a better alignment of the grains. At faster cooling rates of 50°C/h and 100°C/h, non-equilibrium cooling of the partially-melted material occurred. The resulting microstructure is composed of well-aligned, large acicular crystals with length ranging from 5 mm (100°C/h) to 15 mm (50°C/h) and width of around 0.5 mm. These crystals are aligned parallel to the length of the alumina boat.