Solid Solubility In Cu-5 Gd1-Xcax System: Structure, Stability, And Hydrogenation

We report on synthesis and characterization of a novel group of compounds based on copper, gadolinium, and calcium. Cu-Ca and Cu-Gd binaries were previously studied while Ca and Gd are known to be immiscible themselves. The effects of substituting Gd with Ca in Cu5Gd1-XCaX compounds (0 <= X <= 1) were studied by investigating the phase stability and crystal structure of the resulting new compounds in five specimens with X = 0, 0.33, 0.50, 0.66, and 1, respectively. The samples produced by melt-spinning had hexagonal P6/mmm structure, irrespective of Ca amount (..), where lattice parameters varied with.. linearly. This is an indication of good solid solubility under the preparation conditions. A slower cooling upon arc-melting caused the liquid phase separation into Cu4.5Gd and Cu- Ca compounds. Using TEM, rapidly solidified ribbons (Cu5Gd0.5Ca0.5) were investigated and the formation of a homogeneous ternary phase with a nearly nominal stoichiometric composition and minor amounts of Cu- Ca secondary phase was observed. Using DSC and HT XRD, we found that these systems are stable at least up to 400 degrees C. Upon a 16-hour hydrogenation at 1 bar and 300 degrees C, all specimens absorbed about 0.5wt.% of hydrogen. This caused changes in structure with the formation of pure Cu and H(2)Gd1(-X)Ca(X) solid solution.