Effects of stoichiometry, purity, etching and distilling on resistance of MgB2 pellets and wire segments

TL;DR

This study investigates how factors like stoichiometry, purity, and post-treatment affect the electrical resistance of MgB2 superconducting materials, revealing that high purity MgB2 intrinsically exhibits high RRR and low residual resistivity.

Contribution

It provides comprehensive data showing that high RRR and low residual resistivity are intrinsic properties of high purity MgB2, unaffected by non-stoichiometry or wire dimensions.

Findings

RRR varies with boron purity from ~4 to >20

Residual resistivity can be as low as 0.4 μΩ·cm

High purity MgB2 intrinsically has high RRR and low resistivity

Abstract

We present a study of the effects of non-stoichiometry, boron purity, wire diameter and post-synthesis treatment (etching and Mg distilling) on the temperature dependent resistance and resistivity of sintered MgB2 pellets and wire segments. Whereas the residual resistivity ratio (RRR) varies between RRR \~ 4 to RRR > 20 for different boron purity, it is only moderately affected by non-stoichiometry (from 20% Mg deficiency to 20% Mg excess) and is apparently independent of wire diameter and presence of Mg metal traces on the wire surface. The obtained set of data indicates that RRR values in excess of 20 and residual resistivities as low as rho{0} ~ 0.4 mu Ohm cm are intrinsic material properties of high purity MgB2.