Substitute effects of Ga on in superconducting Zr2(Co1−xGax)

As revealed in the powder X-ray diffraction and crystallographic data, the body-centered tetragonal structure of the parent compound Zr2Co is retained in Zr2(Co1−xGax) up to the solubility limit near x = 0.3 . Variation of room temperature lattice parameters indicates that parameter a increases linearly with increasing x up to x = 0.2 then saturates while c and c / a values decrease linearly with x up to x = 0.3 due to doping with Ga. A prominent maximum in the unit cell volume v versus x curve therefore appears around x = 0.2 . Magnetic and electrical measurements show that there is an explicit maximum T c close to x = 0.05 . This demonstrates that the superconducting transition temperature of the pseudo-binary system Zr2(Co1−xGax) is not a monotonic function of the lattice constants a , c , c / a , or v . As compared with the Zr2(Co1−xNix) system, it is suggested that the superconducting transition temperature in Zr2(Co1−xGax) may relate more to the spin density fluctuations than to the density of states at the Fermi level.