Superconducting properties of Zn and Al double-doped Mg 1− x(Zn 0.5Al 0.5) xB 2

Abstract

A series of polycrystalline samples of Mg 1− x (Zn 0.5Al 0.5) x B 2 (0⩽ x⩽0.8) were prepared by solid state reaction method and their structure, superconducting transition temperature ( T c) and transport properties were investigated by means of X-ray diffraction (XRD), ac susceptibility, magnetization and resistivity. The double doping leads to decreases in both the lattice parameters a and c, and the T c decreases with increasing dopant content. A systematical comparison with Al doped- and Li, Al double doped MgB 2 of structure, superconducting transition and critical current density ( J c) is made. It is suggested that the chemical pressure effect plays a more important role influencing the normal state transport and T c than the change of carrier concentration, and the introduction of disorder into the Mg layers shows little influence improving the irreversibility field and J c.