Chemical pressure effect on the superconductor MgCNi3

In order to investigate the positive and negative pressure effects on superconducting properties for MgCNi3, chemical pressure was applied by means of Zn-doping to Mg site (Mg1−xZnxCNi3) and by substituting Mg with Cd (CdCNi3). The lattice constant decreases (increases) with increasing Zn (Cd) content. In the magnetic measurements, superconducting transition temperature (Tc) is decreasing with increasing Zn content and disappears at x > 0.3. While for CdCNi3, Tc also decreases down to 3.4 K. The result seems not to be fully understandable in the case of CdCNi3 since Tc seems to rise owing to the increase of density of states at Fermi energy caused by lattice expansion.