Solid Solubility in Cu5Gd1−xCax System: Structure, Stability, and Hydrogenation

Abstract EN

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 (x), where lattice parameters varied with x 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°C.

Upon a 16-hour hydrogenation at 1 bar and 300°C, all specimens absorbed about 0.5 wt.% of hydrogen.

This caused changes in structure with the formation of pure Cu and H2Gd1-xCax solid solution.