High-pressure synthesis of pure and doped superconducting MgB2 compounds

TL;DR

This study investigates how doping MgB2 with various elements affects its superconducting properties, finding that only aluminum effectively substitutes into the lattice without enhancing performance.

Contribution

It provides a comprehensive high-pressure synthesis analysis of doped MgB2, clarifying which dopants influence superconducting characteristics and the limitations of doping for performance improvement.

Findings

Al substitutes on Mg site, others form secondary phases

No improvement in critical current or Tc with doping

High-pressure synthesis used for sample preparation

Abstract

Superconducting properties of bulk, dense, pure MgB2 and doped (Mg1-xAx)B2 samples with A = Na, Ca, Cu, Ag, Zn and Al were studied for compositional ranges 0 < x < 0.20. The effect on pinning properties and critical current were investigated, particularly for A = aluminium. The samples were sintered and/or synthesised at high pressure - high temperature in a cubic multi-anvils press (typically : 3.5-6 GPa, 900-1000C). They were characterised by x-ray diffraction, scanning electron microscopy and their superconducting properties were investigated by a.c. susceptibility, magnetisation (VSM and SQUID) and transport measurements under magnetic field. Only Al substitutes really on the Mg site. The other elements form secondary phases with B or Mg which do not act as pinning centres. No positive effect is observed on the superconducting properties of the bulk MgB2 samples added with these doping elements : Tc, jc critical current, Hirr and Hc2. For Al, the effect on Hc2 remains small, and the irreversibility line does not move, thus not improving the critical current of the Al-doped MgB2 samples.