Phase Evolution and Superconductivity of Bi-2212 Precursor Powder Prepared by Spray Pyrolysis

Abstract:

The Bi₂Sr₂CaCu₂O_x (Bi-2212) precursor powder was prepared by spray pyrolysis. The phase evolution during the heat treatment process and the superconductivity of wires were analyzed. Results show that the powder prepared by spray pyrolysis is spherical with the average particle size of 3.03 μm and the dispersion distribution. The phase evolution during the heat treatment process of powder includes four main reaction processes. The decomposition of nitrate and the pre-reaction process between components occur firstly at 527 °C. Then the Bi₂Sr₂CuO_x (Bi-2201) phase is formed at 588 °C due to the high reactivity of spray powder. The Bi-2212 phase is generated at 780 °C, and the powder is completely melted at 834.2 °C. The heat treatment temperature window of the Bi-2212/Ag wire is very narrow. The critical current (I_c) is reduced by 31 A when the maximum heat treatment temperature (T_max) is changed by ±2 °C. When the optimal T_max of Bi-2212/Ag wire is 885 °C, the maximum I_c (4.2 K, 0 T) is 486 A. The critical current is increased to 712 A in the oxygen atmosphere during heat treatment.

Key words:Bi-2212;phase evolution;superconductivity