Synthesis of YBa2Cu3Oy superconductors via attrition-milled intermediate oxide precursor containing BaCuO2.5

YBa2Cu3Oy (Y123) phase was synthesized from the oxide precursor containing BaCuO2.5 in two distinct processes. In the first stage, a suitable amount of metallic Y, metallic Cu and barium nitrate (Ba(NO3)2) were mixed via attrition milling for 20 h. After 20 h of milling, the particle size of the powder was in the range of 0.05-0.2 μm. On subsequent heat treatment of the milled powder at 600°C for 5 h with continuous argon flow, the intermediate precursor (IP) was synthesized. The IP contained BaCuO2.5, Y2O3 and CuO and the overall composition of the IP was Y:Ba:Cu:O=1:2:3:7.4. The oxygen content of the IP was higher than that of the corresponding orthorhombic Y123 superconductor. In the second stage, the synthesized IP was converted to the superconducting Y123 phase with heat treatment at 900-1020°C in air without any additional low temperature oxygenation process. A DTA experiment at 20°C/min in air and a series of rapid heat, soak, and quench experiments showed that the BaCuO2.5 constituent of the precursor decomposed at 838°C, which is higher than that of pure BaCuO2.5 (760°C). The results of the TGA experiments suggested that the heating rate had a strong influence on the decomposition temperature of the BaCuO2.5 of the IP. At a heating rate of >50°C/min, the BaCuO2.5 did not decompose completely during heating to 1020°C and form orthorhombic YBa2Cu3O7-x.