Effective incorporation of nanoceria into polycrystalline MgB₂

A series of polycrystalline MgB₂ samples were prepared with different amounts of nanosized CeO₂ inclusions. Samples were subjected to x-ray diffraction, scanning electron microscopy, and atomic force microscopy characterization. We found that nano- CeO₂ inclusions affect the lattice parameters as well as the microstructure of MgB₂ superconductor. An increase in the lattice parameters a and c was observed due to nanoinclusions up to 2 wt %. The morphology of the surface of pure samples reveals a considerable number of weak-links, randomly oriented grains and clean grain boundaries. While in samples with nanoinclusions, grain surfaces and boundaries were decorated with nanosized CeO₂ particles and low traces of secondary phases. A reduction in the average grain size and roughness was also observed for samples with highest inclusions. The superconducting properties have been measured using the magnetization measurement M (H) in magnetic field up to 5 T. Significant enhancement of the superconducting critical current density J_c and the pinning force F_p in applied magnetic field was observed due to nano- CeO₂ addition. However, no considerable change in the transition temperature T_c and transition width was observed. These results were interpreted in terms of the scaling of the flux pinning in granular superconducting networks which leads to a better basic understanding of the performance of MgB₂ system in relatively high applied magnetic fields.