Substitute effects of Ga on Tc 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 Zr-2(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 Zr-2(Co1-xGax) is not a monotonic function of the lattice constants a, c, c/a, or e. As compared with the Zr-2(Co1-xNix) system, it is suggested that the superconducting transition temperature in Zr-2(Co1-xGax) may relate more to the spin density fluctuations than to the density of states at the Fermi level. (C) 2010 Elsevier Ltd. All rights reserved.