Dense MgB2 Ceramics by Ultrahigh Pressure Field-Assisted Sintering

Magnesium diboride (MgB2) ceramics, due to their impressive transition temperature of 39 K for superconductivity, have been widely investigated. The possibility to obtain highly dense MgB2 ceramics with fine microstructure and grain boundaries acting as pinning sites by novel high-pressure-assisted spark plasma sintering (HP-SPS) is reported in this article. HP-SPS was employed to reach 100% density in MgB2 ceramics, and high pressure was utilized in the consolidation of MgB2. An increase in pressure helped in stabilizing the MgB2 phase above thermal decomposition, thus avoiding the formation of non-superconducting phases such as MgO and MgB4. Pressure allowed strengthening of the covalent bond (condensation effect) to increase the thermal stability of MgB2. HP-SPS yielded high mechanical hardness in MgB2 (1488 HV). For better electrical connectivity, which leads to large magnetic moments in high density samples were obtained with the beneficial effect of high applied pressure (1.7–5 GPa) at high temperature (>1000 °C). The combination of the SPS process and high pressure ensured retention of the homogeneous fine microstructure required to obtain high current density and high hardness.