Annealing time effect on Bi-2223 phase development in LFZ and EALFZ grown superconducting fibres

The application of an electrical current during solidification by laser floating zone (LFZ) technique of superconducting fibres of the Bi-Sr-Ca-Cu-O system was recently proposed as a very suitable method to improve crystal alignment. This novel electrical assisted laser floating zone (EALFZ) technique also leads to a strong modification on the phase nature. In the present study, the effect of the annealing time at 860 °C on superconducting properties of Bi₂Sr₂Ca₂Cu₄O₁₁ nominal composition fibres was investigated. Two sets of samples, grown by LFZ and EALFZ using an electric current of 150 mA, were annealed at three different times (24, 96 and 192 h). The critical current density values revealed to be strongly dependent on the 2223 phase amount and on crystal orientation. Current application during the solidification process favours the early development of the 2223 phase, while long annealing times are required in the conventional LFZ processed fibre. The highest critical current density was achieved for the EALFZ fibres annealed during 192 h due to the 2223 stoichiometry optimization and decreasing of second phases.