Effects of Nano-Al doping on superconductivity and microstructure of MgB2 bulk superconductors

Nano-size Al powders were dispersed by ultrasonic vibrations to avoid reuniting and could be doped into the MgB2 bulk materials uniformly. The effects and mechanism of doping were studied. The phase analysis and microstructure analysis show that, Al atoms can enter into the lattice of MgB2 and substitute the site of Mg atoms. The crystal parameters a and c of the MgB2 phase decrease gradually with increase of Al addition, and the value of c is depressed more. The critical temperature T-c drops with the increase of Al addition. The value of T-c is 35.5K for the superconductor with 8mol% addition, while 38.5K for the pure MgB2 bulk superconductor. The properties of critical current density J(c)(B) can be improved at low level doping such as 1mol%,2mol% addition. The results demonstrate that the superconductivity of MgB2 with nano-Al doping is improved at the conditions of low temperature, high magnetic field and low level addition.