Bi–Sr–Ca–Cu–O high-Tc superconductors produced by using a rapid thermal melt processing technique

Abstract

Bi–Sr–Ca–Cu–O high-T_c superconductors have been fabricated using a rapid thermal heat treatment technique. The conventionally sintered pellets were rapidly heat treated for 2 min at 1200 °C with a heating rate of 1000 °C min^–1 and then annealed. The rapidly heat-treated samples exhibited non-superconducting crystalline phases which became superconducting upon annealing in air. A T_c(zero) of 105 K was obtained for the sample annealed at 861 °C for 240 h. 30% Pb was substituted for Bi in order to stabilize the high-T_c(110 K) phase. Correlations between the processing conditions and the resulting properties of sintered and rapidly heat-treated samples have been studied. Based on low-field magnetization data, the low critical field, H_c1, of heat-treated samples was estimated to be 14% higher than that of the as-sintered samples. The bulk density increased by 10% after thermal heat treatments. In the rapidly heat-treated samples, 95% of the phases was estimated to be the high T_c(2223) phase. X-Ray analysis data showed that the undesirable impurity phases were eliminated after heat treatment. Additionally, the effect of the magnetic field on the electrical resistance has been studied as a function of temperature, and Hall effect measurements have been carried out down to the superconducting state from pre-onset conditions to essentially zero resistance.