Limited infiltration due to reactive sintering of nano-Sm < inf > 2 < /inf > O < inf > 3 < /inf > with preforms - Its effect on (Y, Sm)Ba < inf > 2 < /inf > Cu < inf > 3 < /inf > O < inf > 7-δ < /inf > superconductors

Abstract

Preform optimized infiltration growth process (POIGP) is employed to fabricate mixed rare earth (Y, Sm)Ba2Cu3O7-δ superconductors of high performance. POIGP creates wide range of pinning centres and also enables nano-particle additions to stable Y2BaCuO5 (Y-211) preforms. Nano-Sm2O3 particles (30-50 nm) were introduced in 0, 10, 20 and 30 wt.%, homogenously and without agglomeration, into the Y-211 preforms and the corresponding composites YBCO-Ar, YSm-10, YSm-20 and YSm-30 are fabricated. Though all the samples were processed in argon atmosphere to suppress the formation of solid solutions with Sm at Ba site, the effort was successful only in the YSm-20 sample, as seen from sharp diamagnetic transition and XRD studies. Magnetic property measurements were carried out on samples which showed strong (00l) texture, but were not necessarily single crystalline since no seed was used in the experiments. The calculated critical current densities (J c) are thus reflective of the values in the basal plane, in the most favourable direction. The final composites revealed YSm-20 to exhibit better J c with substantial flux pinning up to 9 T, at 77 K. Detailed examination of microstructures and field dependence of J c reveal that the addition of nano-particles is not always rewarding and can lead to reactive sintering of Y-211 and limit the extent of liquid phase inflow into preforms. This not only can lead to incomplete reaction leaving larger 211 particles in the matrix, but can also shift the composition of liquid phase such that it promotes the formation of undesired solid solutions in IG processed REBCO as seen in YSm-30. The effect of various factors like open porosity in the preform, the ease of liquid phase infiltration and the liquid phase composition on the residual 211 size in the composites, suppression of RE/Ba solid solutions, and the resultant J c versus H curves is discussed.