Fabrication of C Doped ${\hbox {MgB}}_{2}$ Wire Using a Mixture of In-situ and Ex-situ P

MgB₂ wires were fabricated using a mixture of doped in-situ and ex-situ powders. The effects of the ratio of ex-situ to in-situ powders on the microstructure and critical properties were evaluated. The wires were processed using a powder-in-tube technique with a series of (MgB₂)_x + (Mg + 1.99B + 0.01C)_1-x, where x = 0, 0.3, 0.5, 0.7, and 1.0. The critical current density (J_c) was measured using both magnetization (5 and 20 K, 1-6.5 T) and transport methods (4.2 K, 4-10 T). Microstructural observations revealed a decrease in the number of Kirkendall voids and an increase in core density, while cracks grew along the longitudinal direction of the wire with increasing x. In addition, the Mg from the in-situ powder acted as a sintering aid, healing cracks and enhancing the connection between the in-situ and ex-situ regions. At x = 0.5 and 1.0, the sample had the highest and lowest T_c and J_c, respectively. On the other hand, the other samples produced using the mixed powders had moderate critical properties, probably due to the mixed morphology of the in-situ and ex-situ microstructure.