New clathrate-like compound Eu7Cu44Sb23-δ: synthesis, crystal and electronic structure, and the effect of As-for-Sb substitution on the magnetic properties

A new intermetallic compound, ternary antimonide Eu7Cu44Sb23-δ [Fm-3m, a = 17.4346(1)Å, δ = 0.5(1)] is reported. The compound forms a continuous substitutional solid solution with its Eu7Cu44As23 archetype. The gradual substitution of Sb for As evokes partial disorder in the copper-pnictogen framework that becomes more pronounced with an increase of the Sb content and changes magnetic properties. Whereas Eu7Cu44As23 is metallic ferromagnet below 17 K, Eu7Cu44Sb23-δ shows paramagnetic behavior down to 1.8 K according to the magnetic measurements, while retaining metallic properties according to the DFT calculations. The origin of the disorder, the structure-property relationships, as well as prospects of further substitution in the anionic sublattice are discussed.