Superconductivity in porous MgB2

TL;DR

This study investigates the effects of porosity on the superconducting properties of MgB2, revealing that superconductivity persists down to a critical density and that critical temperature and current density are affected by porosity.

Contribution

It demonstrates the formation of a linked superconducting structure in porous MgB2 down to the percolation threshold and analyzes how porosity influences critical temperature and current density.

Findings

Superconductivity persists down to a normalized density of 0.16.

Critical temperature decreases with increasing porosity, reaching 32K at the threshold.

Critical current density remains high (~3×10^5 A/cm^2) at 20K for certain porosity levels.

Abstract

Porous magnesium diboride samples have been prepared by the heat treatment of a pressed mixture of Mg and MgB2 powders. It was found that linked superconducting structure is formed down to the minimum normalized density gamma= d/do= 0.16 (percolation threshold), where d is the density of MgB2 averaged over the sample, do= 2.62 g/cm3 is the X-ray density. Lattice parameters and critical temperature of the porous sample decrease with increasing porosity (decreasing gamma) and Tc2= 32K is minimal at gamma= 0.16. The grain boundaries in the porous samples are transparent for the current and Jc~3.105A/cm2 in self field at T= 20K in the samples with gamma~ 0.24.