Densification behavior during hot pressing of Bi-Pb-Sr-Ca-Cu-O superconductors

Bi1.84Pb0.34Sr2.03Ca1.9Cu3.06Oy bulk superconductors with various relative densities were prepared by hot pressing in the temperature range 780 degrees C-840 degrees C and the pressure range of 4.9 MPa-24.5 MPa in air for 2 h. The relationship between porosity, p, and hot pressing conditions was formulated using the following equation: In(p) = -alpha(o) exp(-E/RT)P + In(p(o)), where P was the hot-pressing pressure, p(o) the porosity of the compact body, E an apparent activation energy for densification, T the temperature, R the gas constant, and alpha(o) a constant. The apparent activation energies were 184 KJ/mol and 526 KJ/mol in the lower- and higher-temperature ranges in comparison to 820 degrees C, respectively. The densification mechanisms in the lower and higher temperature ranges are discussed in terms of plastic flow, particle rearrangement and the formation of liquid phase.