Abstract
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.
Highlights
Superconductors are materials whose conductivity tends to infinite as resistivity tends to zero at a critical temperature
Dense MgB2 polycrystalline samples were prepared by an in-house built ultrahigh pressure
MgB2 fully dense ceramics were obtained by maintaining the microstructured grains and by stabilizing the initial MgB2 phases
Summary
Superconductors are materials whose conductivity tends to infinite as resistivity tends to zero at a critical temperature. MgB2 is one of the potential light materials with a medium critical temperature (Tc = 39 K) for diverse applications requiring improvement of the superconducting properties. It has a high charge carrier density, 1.7–2.8 × 1023 A/cm , a high critical current density Jc of about 107 A/cm (4.2 K, 0 T), as well as high coherency lengths ξab (0) = 37,120 Å and ξc (0) = 16–36 Å. MgB2 can be used as an alternative to other low-temperature superconductors such as NbTi and. MgB2 has a hexagonal crystal structure and is an intermetallic with simple stoichiometry [1,2]
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