The spatial distribution of temperature and oxygen deficiency in spark-plasma sintered superconducting Bi-based materials

Schematic-drawing-of-the-consolidation-system — (a) Schematic drawing of the consolidation system, (b) boundary conditions, (c) simulation by FEM of the temperature distribution of the whole system (see details in the text), and (d) expanded view of the temperature distribution of the die-sample region and the radial temperature profile for z=0.

Writers: E. Govea-Alcaidea, J.E. Pérez-Fernándeza, I.F. Machadob, R.F. Jardimc,

Keywords: Bi-based superconductor; Granular material; Spark-plasma sintering; Finite element method; Transport properties

Abstract: Pre-reacted powders of (Bi–Pb)₂Sr₂Ca₂Cu₃O_10+δ (Bi-2223) were consolidated by using the spark plasma sintering (SPS) technique under vacuum and at different consolidate temperatures T_D. X-ray diffraction patterns revealed that the dominant phase in all SPS samples is the Bi-2223 phase, but traces of the Bi₂Sr₂CaCu₂O_10+x (Bi-2212) phase were identified. We have found that the transport properties of SPS samples depend on their oxygen content because the SPS process is performed under vacuum. Simulations by using the finite element method (FEM) were performed for determining the actual temperature in which powders are consolidated. From these results we have inferred that SPS samples are oxygen deficient and such a deficiency is more marked near the grain boundaries, suggesting the occurrence of grains with core–shell morphology. We also argued that the width of the shell depends on the consolidation temperature, a feature corroborated by the FEM simulations.