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

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 degrees C under the H-2 pressure of 3 MPa. Quenching prevented the phase transformation of beta-Mg(BH4)(2) -> alpha-Mg(BH4)(2) upon cooling, and the dominant point-pinning effects originated from the self-generated nano-sized beta-Mg(BH4)(2) particles that were confined within the MgB2 grains. A semi-coherent relationship was found between MgB2(100) and Mg(BH4)(2)((1) over bar1 (4) over bar) 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.