Superconductivity in non-cubic crystal structures

Superconductivity has been observed in alloy samples of the zirconium-germanium, hafnium-germanium, yttrium-germanium and lanthanum-germanium systems. The samples were prepared on heated substrates, under varying conditions by r.f. sputtering technique. The composition span was from 20 to 90 at.% Ge. Superconductivity was found in all four of these systems and was identified with the digermanide phase by X-ray analysis. Four terminal resistive measurements show the following superconducting transitions: 8 K (ZrGe2), approximately 2.2 K (HfGe2), 3.8 K (YGe2) and 2.65 K (LaGe2). Annealing studies indicate that the superconducting ZrGe2 and HfGe2 phases are metastable, and depend strongly on the conditions of synthesis. (author)