Synthesis of Nd123 superconducting powder via oxalate coprecipitation

Abstract

The preparation of pure and fine Nd123 powder was investigated in five ways. Precursor powders were generated by the oxalate coprecipitation. Some of the powders were heated in vacuum (770°C for 20 h at 10–15 Pa), followed by calcination at different temperatures and oxygen partial pressures. The vacuum step was omitted with the remaining powders. Calcination under pure oxygen requires excessively high temperatures ( T>940°C). Under these conditions the powder is badly fused, with grain sizes in the 7–12 μm range. In addition, the orthorhombicity of this powder is low due to the formation of Nd123 solid solution — implying the presence of residual BaCuO 2. The optimal route to produce the desired powder is in a low partial pressure of 350–1000 ppm oxygen in nitrogen, without a vacuum preheating step. Similar powders can be obtained in 1% O 2 with a vacuum preheating step. At 60 ppm O 2 the reaction between Nd 1+ x Ba 2− x Cu 3O 6.5+ x/2+δ and BaCuO 2 is incomplete, with about 5% of barium cuprate remaining. Finally, the T c of the powder produced at the optimal conditions was found by DC magnetization to be ∼ 99 K.