Formation of the 110-K superconducting phase via the amorphous state in the Bi-Sr-Ca-Cu-O system

The thermodynamic and kinetic behavior of both the 85 and 110-K superconducting phases during the crystallization annealing process have been observed and analyzed using x-ray diffraction, magnetic shielding, and resistivity measurements in crystallized Bi-Sr-Ca-Cu-O glasses with nominal compositions Bi₂{Sr}₂Ca₂{Cu}₃Oₓ (2:2:2:3), Bi₂{Sr}₂Ca₃{Cu}₄Oₓ (2:2:3:4), and Bi₂{Sr}₂Ca₄{Cu}₅Oₓ (2:2:4:5). A single superconducting transition near 110 K has been observed in both resistive and magnetization shielding experiments for crystallized samples with 2:2:3:4 and 2:2:4:5 nominal compositions. Eutectic crystallization occurs during annealing of rapidly solidified glass samples. Both the 85-K and Ca₂{CuO}₃$ phases cooperatively nucleate and grow from the amorphous matrix. The 110-K phase subsequently forms at the interfaces between the eutectic products, controlled by calcium and copper diffusion. A phase-change cycling has been observed, during which the 110-K phase increases in volume percent with increasing annealing time at 870 ^∘{}C in calcium- and copper-rich samples. It then vanishes as annealing is prolonged at the same temperature. This behavior also occurs with different time periods depending on the initial calcium and copper composition of the samples. Microstructural changes associated with such cycling have also been observed. Also discussed are crystallization mechanisms, diffusion phenomena, and related superconducting properties.