Superconducting Properties of Carbon and Zn Double-doped Mg1−xZnx(B1−xCx)2

A series of polycrystalline samples of Mg 1− x Zn x (B 1− x C x ) 2 ( x =0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) were synthesized by a conventional solid-state reaction method under a background pressure about 10 −3 Pa. Phase identification, crystal structure and superconducting transition temperature ( T c ) were studied by means of X-ray diffraction (XRD) and resistivity measurements. The results indicated that the lattice parameters a and c show no clear trend in their changes with increasing doping level, and it turned out that the dopants had a marked effect on the crystal-lattice parameters and changed the crystal structure of the samples. The T c for Mg 1− x Zn x (B 1− x C x ) 2 decreased with C and Zn doping, but the rate of decrease was slower than single C-doped. We propose that the suppression of T c by doping originates largely from the structural change.