Chemical interactions in Ti doped MgB₂superconducting bulk samples and wires

Abstract

Magnesium diboride superconducting wires and bulk samples synthesized at high pressure have been produced with a variety of reactive metal additions. All these samples showed high critical current densities, but here we are most interested in the striking result that reactive metal additions such as titanium substantially improved the critical current values, but had little detrimental effect on Tc values. For instance, the critical current values in the wires could be increased by more than a factor of 3.5 at 4 K and 10 T by the inclusion of up to 10 wt% of Ti. In bulk materials the Jc values can be increased by even larger values, and the irreversibility field at 20 K increased to above 7 T. In a detailed study of the microstructure of these materials we have shown that PIT ex situ wires with 10 wt% titanium additions have a complicated layered microstructure around the Ti-rich particles, possibly forming titanium–boron phases, but also incorporating impurity elements including hydrogen. X-ray diffraction data, TEM and elemental mapping in the NanoSIMS confirmed the surprising suggestion that samples synthesized at high pressure from Mg and B with Ti additions contain a titanium hydride. These new compositional data support the idea that reactive metal additions are extremely beneficial in MgB2 wires and bulk materials because they preferentially adsorb deleterious impurities from the superconducting matrix.

High Critical Current Density MgB2

“…The reaction kinetics between magnesium and boron can be modified by chemical or compound dopants [66], which influence the grain shape and size [67,68], the secondary phases [69], MgB 2 density [70], and the element stoichiometry [71]. Carbon doping is one of the most promising methods to improve the superconducting performance of MgB 2 .…”

Formation of Higher Borides During High-Pressure Synthesis and Sintering of Magnesium Diboride and Their Positive Effect on Pinning and Critical Current Density

“…Ta and Ti transform into hydrides by adsorbing impurity hydrogen (which may come from the high-pressure cell materials), thus preventing the formation harmful for [5], [6]. The formation of only at 800 , 2 GPa was confirmed by TEM and NanoSIMS ion mapping [13]. may increase the nucleation barrier of restricting its formation, but this calls for further study.…”

Modern superconductive materials for electrical machines and devices working on the principle of levitation

“…The presence of TiH 1.924 has been a surprise since titanium hydrides are relatively unstable compared to the more common titanium compounds, particularly the oxide phases for which we expect the constituent elements to be readily available in these impure ceramics. Enthalpy of formation values illustrating the relatively low stability of this titanium hydride is given in Table 2 [23].…”