Synthesis temperature effects on ex-situ manufactured MgB2 wires useful for power applications

• We investigate superconducting properties of ex-situ MgB2 wires made from laboratory-synthesized boron.
• We investigate the influence of temperature synthesis of MgB2 on the superconducting and morphological properties.
• It has been found the suitable synthesis procedure to enhance critical current density.
• A correlation between synthesis temperature and average grain size has been given, using different procedure.

Ex-situ powder in tube manufacturing process is based on the filling of a metal sheath with pre-synthesized MgB2 powders. It is necessary for MgB2 used in wire manufacturing to have the required properties of grain size and connectivity. Synthesis temperature for MgB2 is an important parameter to improve the quality of powders and subsequently enhance performances of wire for large-scale applications. In this work we investigated the effect of synthesis temperature on morphology, and how this is reflected on superconducting properties. A detailed study on the influence of MgB2 synthesis temperature on grain size has been given, evaluated through SEM images and magnetic measurement. As predicted higher synthesis temperature led to an enhancement in average grain size, but the effect is slightly appreciable. It has been applied a model for average grain size distribution based on the penetration of magnetic field in the superconductor, that was found to be in agreement with several other methodologies, in order to have a confirm of image analysis. Engineering current density has been evaluated from direct measurement using a four-probe configuration, where best results have been reported for sample synthesized at 950 °C, with engineering current density of 3 × 105 A/cm2 at 2 T, almost two times the value of sample synthesized at 750 °C at the same field.