Substitution effect of Zn and Cu in MgB2 on Tc and structure

The investigation of Zn substitution in MgB2 polycrystalline samples shows that about 0.1 Zn can be substituted in the structure of Mg deficient samples while it can not be substituted in stoichiometric MgB2. As a result of the isovalent Zn substitution into the Mg position of Mg deficient samples the a and c lattice constants increase by about 0.17% and 0.2% respectively. Susceptibility measurements show a slight lowering of T,by about 0.5 K for 0.05 Zn, which decreases to 0.2 K for 0.1 Zn substitution. Investigation of the pressure derivative of T-c shows dT(c)/dp = -0.15 K/kbar independent of Zn content. Substitution of Cu leads to multiphase samples without any changes of lattice constants, which indicates that Cu does not enter the structure of MgB2. The Cu substitution broadens the superconducting transition considerably, while the onset remains unchanged. (C) 2001 Elsevier Science Ltd. All rights reserved.