Microstructure and critical current of bulk MgB₂ superconductor

Abstract

The structure of bulk MgB2 specimens after cold deformation in Bridgeman anvils and “Toroid” chamber and following recovery annealings has been studied by scanning and transmission electron microscopy. It is demonstrated that in spite of the matrix phase grain coarsening by 5-7 times under annealing compared to the as-deformed state, the critical current density increases by a factor of 3 (6.7×104 A/cm2 at 30 K after deformation in the “Toroid” chamber and recovery annealing).

Dense MgB2 Ceramics by Ultrahigh Pressure Field-Assisted Sintering

“…From the literature review [1][2][3][4][5][6][7][8][9][10][11][12], it can be inferred that the thermal decomposition of MgB 2 starts around 830 • C. We performed conventional SPS experiments at 100 MPa with a dwell time of 5 min and observed that thermal decomposition appeared at 1050 • C. The shift of this thermal decomposition to a higher temperature can be attributed to the benefit of 100 MPa pressure under pulse electric current. We further observed by conventional SPS that when the applied pressure was increased, the crystallite size decreased at 950 • C, as shown below.…”

“…Various research teams reported on employing recent techniques such as field-assisted sintering or high-pressure-assisted sintering techniques [8][9][10][11][12] to obtain MgB 2 dense compact samples with relative densities greater than 95%, in comparison with other conventional pressureless sintering techniques. The influence of the sintering parameters in field-assisted sintering, such as pressure, dwell time, temperature, and heating/cooling rate, on the structural, microstructural, and superconducting properties of MgB 2 have been studied [8][9][10][11][12]. An increase in the relative density of MgB 2 up to 99% was achieved when the sintering temperatures were in the range of 900-1050 • C [5].…”

“…The application of pressure (as a "driving force") manifests itself in different ways such as reduced sintering temperature leading to conservation of grain size and sintering the high-pressure structural phase of alumina [15]. Krinistina et al [12] reported on obtaining dense MgB 2 samples by employing high-pressure deformation and annealing, which also resulted in obtaining nanostructured ceramics with increased critical current density in spite of the presence of MgO formed in the grain boundaries. Application of high pressure leads to increased critical current density, necessary for the superconducting properties of MgB 2 ceramics.…”

“…In the present work, we used our in-house built high-pressure SPS equipment [8][9][10][11][12], which enables a maximum pressure of 6 GPa and temperatures up to 1800 • C to be reached, given its versatility, for the synthesis and sintering of highly dense MgB 2 ceramics at low temperature. Our HP-SPS equipment, capable of reaching 3000 A for 10 V with a pulse of 3.3 ms, was employed by using the Belt system to generate a high pressure up to 6 GPa, but other possibilities such as the Bridgman system could also be employed [13].…”