Confinement of self-generated Mg(BH4)2 particles for simultaneously enhanced flux pinning and grain connectivity in polycrystalline H-doped MgB2

Abstract

The present study reports a simple quenching method to simultaneously improve flux pinning and grain connectivity in polycrystalline H-doped MgB2, which was ex-situ synthesized at 350 °C under the H2 pressure of 3 MPa. Quenching prevented the phase transformation of β-Mg(BH4)2→α-Mg(BH4)2 upon cooling, and the dominant point-pinning effects originated from the self-generated nano-sized β-Mg(BH4)2 particles that were confined within the MgB2 grains. A semi-coherent relationship was found between MgB2(100) and Mg(BH4)2() planes. Meanwhile, the precipitation-induced expansion of the MgB2 grains remained at room temperature, leading to an increasing number of contact points as well as grain connectivity. Compared with the un-doped MgB2, the quenched H-doped one exhibited enhanced critical current density over the entire field. These results are expected to guide the design of flux pinning centers for improving the J c performance of standard type II superconductors.