Kinetics and Formation of the 110 K Phase in the Bismuth-Lead-Strontium-Calcium-Copper-Oxygen System

The kinetics and formation of the 110 K superconducting phase in the Bi‐Pb‐Sr‐Ca‐Cu‐O system have been analyzed via Avrami theory, high‐temperature X‐ray diffractometry, scanning and transmission electron microscopy, and differential thermal analysis techniques. The kinetic study indicates that the reaction is diffusion controlled for oxygen partial pressures of ˜1‐35 kPa (0.01‐0.35 atm). The appearance of liquid increases the contact area of the reactant particles, thus accelerating mass transport and the phase formation kinetics. The 110 K phase forms via reaction between the 80 K phase, secondary phases that are rich in calcium and copper, and the liquid that contains lead, calcium/strontium, and copper.