Cu5In3‐Cu3In2 Revisited

Abstract

The η‐phase field of the Cu–In system is unusually rich and shows wealth of phases that are all related to the B8 (NiAs/Ni2In) type. Previous electron diffraction work has revealed extensive super structure ordering; in this study, we report single crystal diffraction experiments on high‐quality samples of two of the phases in the system, ht1‐Cu5In3 and ht2‐Cu5In3. Both these phases constitute super structures, caused by the ordering of interstitials. The structure ht2‐Cu5In3 is a relatively simple structure with a bidimensional modulation but where only first order satellites are visible, indicating incomplete order whereas ht1‐Cu5In3 displays many high order satellites and the refined structure exhibit nearly perfect order with step‐function‐like occupancy domains. The refinement of the structure of ht1‐Cu5In3 is challenging for several reasons. It is difficult to integrate the data because of the unusual combination of very closely spaced satellites caused by q‐vectors close to (1/3 1/3 0) and a paucity of reflections in total, caused by the small substructure. A second challenge is the refinement of what amounts to a two‐dimensional step function. In effect, the shape of a two‐dimensional occupation domain is defined by a Fourier series and the problem of defining that shape is non‐trivial.