Structure and Superconductivity of (MgB2−xCx)0.97Cu0.03

A series of samples of (MgB2−xCx)0.97Cu0.03 (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) and MgB2 were synthesized by a solid state reaction method. The structure, superconducting transition temperature and transport properties of the samples were studied by means of X-ray diffraction (XRD) and resistivity measurements. It is found that the c-axis of the lattice remains unchanged with increasing C doping, while the a-axis shows a small decrease. The Tc of the samples steadily decreases with increasing C doping. It is suggested that the chemical pressure effect plays a more important role influencing the normal state transport and Tc than the change of carrier concentration.