Effect of Nano-AlN Addition on the Critical Current Density of MgB2 Superconductors

Abstract

A series of MgB2 polycrystalline pellets with and without aluminum nitride (nano)addition have been synthesized by a solid-state reaction. No detectable shift in the XRD peak position of MgB2 has been observed with AlN nanoparticles addition indicating no substitution for Mg or B. Surface morphology displays randomly oriented well-defined grains. The presence of AlN nanoparticles between the grain boundaries and also on the grain surface is observed in AlN-added MgB2. Addition of AlN nanoparticles decreases the superconducting transition temperatures from 38.5 to 37 K. Resistivity data confirm an improved connectivity of the grains in MgB2 pellets for low-level addition of AlN nanoparticles. Magnetization data measured at various temperatures between ±6 T are used to estimate the critical current density (Jc) of undoped and AlN nanoparticles doped MgB2 pellets. Jc enhances significantly up to 4 T at 20 K for MgB2 containing 0.5 wt.% AlN. Our analysis confirms excellent correspondence of the measured field dependence of critical current density (Jc) in terms of collective pinning model. A new universal scaling behavior is established between the reduced critical current density, Jn(=Jc/Jc(0)) and the reduced field hn(=H/H0) for both undoped and AlN-doped MgB2 pellets at different temperatures, where Jc(0) and H0 are the best fit parameters obtained from the collective pinning model. Our analysis further confirms the dominance of δTc-type pinning for pure MgB2, and for n-AlN-added MgB2 pellets at low temperatures the major contribution comes from δl-type pinning.