Influences of heat treatment and doping on microstructure and superconducting properties of MgB₂ superconductor

The microstructure and superconducting properties of pure, Ti and Zr doped MgB₂, which synthesized by solid reaction method. The heat treatment temperature are varied from 650 to 800 °C at ambient pressure. It is found that heat treatment temperature have obvious effect on grain size and MgB₂ grains are greatly refined at 750 °C. Besides, Zr does not occupy the atomic site in the MgB₂ crystal structure, but forms ZrB₂ particles in the MgB₂ matrix. The results of superconducting properties show that Mg_0.9Zr_0.1B₂ have the highest J_c value sintered at 800 °C. It is argued that the microstructure features with good grain connectivity of the Zr doped MgB₂ fabricated at optimize heat treatment temperature may take the responsibility for the enhancement of J_c in Zr-doped MgB₂ bulk superconductor. The results show a good potential to fabricate high performance MgB₂ bulks and wires at ambient pressure on an industrial scale.