Decomposition of (Bi,Pb)-2223 phase during sinter forging

Abstract

Sinter forging is one of the pressure sintering methods, in which the side surface of a sample is free during uniaxial pressing at high temperatures. Such a condition caused unique phenomena in the decomposition of (Bi,Pb)-2223 phase. Bi 1.84Pb 0.34Sr 2.03Ca 1.9Cu 3.06O y bulk superconductors were sinter-forged at the temperature range of 840–870°C and under the pressure of 9.8 MPa in air for 20 h. The (Bi,Pb)-2223 phase decomposed to (Sr,Ca) 2CuO 3 phase and a liquid phase at high temperatures, followed by the extrusion of the liquid phase from the inner part to the outer part of samples due to the uniaxial pressure. Therefore, the decomposition of the (Bi,Pb)-2223 phase in the sinter forging was slow compared with that in the normal sintering or the hot pressing. The critical current increased with increasing sinter forging temperature. It was worth-noting that the sample sinter-forged at 870°C had the highest J c in spite of the highest content of (Sr,Ca) 2CuO 3 phase. The high-temperature heat treatment was effective for the improvement of grain coupling. A better way in sinter forging is discussed for increasing J c.