Effect of higher borides and inhomogeneity of oxygen distribution on critical current density of undoped and doped magnesium diboride

TL;DR

This study investigates how doping and inhomogeneities like higher borides and oxygen distribution affect the critical current density in magnesium diboride, revealing new mechanisms and optimal synthesis conditions for enhanced superconducting properties.

Contribution

It introduces a novel understanding of doping effects on flux pinning and demonstrates optimal synthesis parameters for high-performance MgB2 superconductors.

Findings

SiC doping yields jc= 1,000,000 A/cm² at 1 T and 20 K

Undoped MgB2 synthesized at 2 GPa, 600°C shows jc= 100 A/cm² in 10 T

MgB12 matrix materials exhibit doubled microhardness and high superconducting volume

Abstract

The effect of doping with Ti, Ta, SiC in complex with synthesis temperature on the amount and distribution of structural inhomogeneities in MgB2 matrix of high-pressuresynthesized-materials (2 GPa) which can influence pining: higher borides (MgB12) and oxygen-enriched Mg-B-O inclusions, was established and a mechanism of doping effect on jc increase different from the generally accepted was proposed. Near theoretically dense SiC-doped material exhibited jc= 1000000 A/sq. cm in 1T field and Hirr =8.5 T at 20 K. The highest jc in fields above 9, 6, and 4 T at 10, 20, and 25 K, respectively, was demonstrated by materials synthesized at 2 GPa, 600 oC from Mg and B without additions (at 20 K jc= 100 A/sq. cm in 10 T field). Materials synthesized from Mg and B taken up to 1:20 ratio were superconductive. The highest jc (60000 A/sq. cm at 20 K in zero field, Hirr= 5 T) and the amount of SC phase (95.3 percents of shielding fraction), Tc being 37 K were demonstrated by materials having near MgB12 composition of the matrix. The materials with MgB12 matrix had a doubled microhardness of that with MgB2 matrix (25 GPa and 13.08 GPa, at a load of 4.9 N, respectively).