Grain boundaries and pinning in bulk MgB₂

Abstract

We report the grain size dependence of critical current and grain boundary pinning in bulk MgB2. By combining polarized optical microscopy and electron backscatter diffraction, we obtain evidence of special grain boundaries with a high density of dislocations that are able to provide high critical current in MgB2 polycrystals. We argue that reduction of grain size to the nanoscale level is sufficient to provide the critical current densities required for large-scale applications at the boiling temperature of liquid hydrogen.

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

“…17,18 Carbohydrates easily decompose at, or even below 650 1C, the melting temperature of magnesium, which enables low sintering temperature fabrication to suppress grain growth. Smaller grains are related to larger pinning force and higher critical current, [19][20][21][22] according to grain boundary pinning models. It is also claimed that more homogeneous mixing is possible than with other doping methods.…”

Critical current density and flux pinning in Zr0.96V0.04B2 superconductor with AlB2 structure

“…This microstructure could have an influence on flux pinning and critical current density. 24 Figure 2(a) presents a well defined superconducting transition of a new superconducting Zr 0.96 V 0.04 B 2 compound. The temperature dependences of its magnetization (M) were measured in a field of 0.5 Oe.…”

Permanent magnet with MgB2 bulk superconductor

“…Because of its high T c (40 K) and recent progress in high-performance cryocoolers, it is a strong contender for future cryocooled, liquid-helium-free applications at 5-30 K. In practice, the distinct advantage of MgB 2 is that its metallic superconductivity (i.e., it's simple and symmetric pairing mechanism, high carrier density, and long coherence length) drives a weak-link-free supercurrent flow across grain boundaries, and this occurs even in untextured polycrystalline bulks [20] . Moreover, the nanoscale grain boundaries strongly pin the flux quantum [21][22][23][24] , and in superconducting bulk magnets, this effect is expected to yield strong, uniform, and stable magnetic fields. We recently found that a MgB 2 bulk with a large trapped magnetic field can be synthesized by simple sintering; a technique that can lead to the low-cost, high-yield, and scalable production of superpowerful liquid-helium-free magnets.…”