Critical current densities of superconducting MgB2 tapes prepared on the base of mechanically alloyed precursors

High Critical Current Density MgB2

“…A high temperature heat treatment is necessary for the ex-situ process to improve the connectivity [99][100][101][102]. This heat treatment leads to recrystallization and H c2 reduction [25]. It is concluded that disorder induced by the low temperature processing is insufficient for high superconducting performance of the ex-situ MgB 2 .…”

“…On the other hand, dirty grain boundaries do potentially reduce the critical current [21]. Insulating phases on the grain boundaries, such as MgO, boron oxides [22] or boron carbide [23], normal conducting phases [24], porosity, and cracks [25], can further reduce the cross-section effective of supercurrents. The high porosity in in-situ prepared MgB 2 is responsible for its low density, only about half (or less) of its theoretical value [26].…”

“…The in-situ route is a practical technique to improve the H c2 and J c performance of MgB 2 using magnesium or MgH 2 as the precursor material [30][31][32][33][34][35][36][37][38][39], which reacts with boron after mixing and compacting. Low annealing temperature generates MgB 2 samples with small grains [25,[40][41][42][43][44][45][46][47][48][49][50][51][52] due to the poor crystallinity, and the great amount of grain boundaries result in strong pinning and high H c2 . Magnesium deficient samples can be fabricated by adjusting the stoichiometry of the precursor materials.…”

In-situ studies of Fe2B phase formation in MgB2wires and tapes by means of high-energy x-ray diffraction

“…[12] Fischer et al [13] Xu et al [14] Interface reaction layer thickness [μm] Sintering temperature [ example. On the other hand, the samples prepared from pre-reacted MgB 2 powders (ex-situ process) show a clearly different behaviour, the interface reaction taking place at higher temperatures.…”

Effect of fabrication process on the superconducting properties of MgB2 tapes

“…Based on these factors, various methods have been tried to improve the J c characteristic of MgB 2 [4][5][6][7]. On the other hand, the superconducting properties of MgB 2 were also affected by the fabrication technique [8] and the starting material processing technique [9].…”