A Study of Calcination Conditions for Synthesizing Fine Particles of (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O _y and (Nd_0.33Eu_0.33Gd_0.33)₂BaCuO₅

Abstract

The calcination temperature was studied for optimum processing conditions for preparing (Nd_0.33Eu_0.33Gd_0.33) Ba₂Cu₃O _y (NEG-123) and (Nd_0.33Eu_0.33Gd_0.33)₂BaCuO₅ (NEG-211) powders with good quality and fine size. This study used commercially available raw powders of Nd₂O₃, Eu₂O₃, Gd₂O₃, BaO₂, and CuO in a purity of 99.9 % with 3–5- μm particle size. These raw powders were carefully weighed to have the compositions of NEG-123 and NEG-211 and pressed into pellets 25 g in weight. The samples were placed in a box furnace under ambient atmosphere and heated to temperatures of 820, 840, 860, and 880 ^∘C at a rate of 100 ^∘C/h, held there for 24 h, followed by cooling at 100 ^∘C/h. X-ray diffraction analyses showed that almost all the samples are single phase except NEG-123 processed at 820 ^∘C. The average particle size of NEG-123 powders increased with increasing processing temperatures, while that of NEG-211 remained in the same range below 5 μm irrespective of the treatment temperature. Since the particle size of NEG-123 powders was around 10 mm, one need to refine the particle size below 5 μm with a technique like mechanical grinding for the production of high J _c NEG-Ba-Cu-O bulk super conductors. NEG-211 powders will be suitable for such a use in the present form. The homemade powders were used to fabricate NEG-Ba-Cu-O bulk by cold top seeding melt growth with MgO seed following by oxygen annealing treatment. The characterization of bulk demonstrated critical temperature at 65 K with maximum critical current density of 70,000 kA/cm ² at 10 K with H//c-axis.