Ca 3 Ag 1+ x Ge 3– x ( x = 1/3): New Transition Metal Zintl Phase with Intergrowth Structure and Alloying with Aluminum Metal

Abstract. The ternary Zintl phase Ca 3 Ag 1+ x Ge 3– x ( x = 1/3) was synthesized by the high‐temperature solid‐state technique and its crystal structure was refined from single‐crystal diffraction data. The compound Ca 3 Ag 1.32 Ge 2.68(1) adopts the Sc 3 NiSi 3 type structure, crystal data: space group C 2/ m , a = 10.813(1) Å, b = 4.5346(4) Å, c = 14.3391(7) Å, β = 110.05(1)° and V = 660.48(10) Å 3 for Z = 4. Its structure can be interpreted as an intergrowth of fragments cut from the CaGe (CrB‐type) and the CaAg 1+ x Ge 1– x (TiNiSi‐type) structures, and it therefore represents an alkaline‐earth member of the structure series with the general formula R 2+ n T 2 X 2+ n with n = 4. Unlike the rare‐earth homologues that are fully ordered phases, one seventh of the atomic sites in the unit cell of the title compound are mixed occupied (roughly 2/3Ge and 1/3Ag), and this can be explained by the Zintl concept. The alloying of this phase using aluminum metal yielded the isotypic solid solution Ca 3 (Ag/Al) 1+ x Ge 3– x , in which the aluminum for silver substitution is strictly localized in the TiNiSi substructure, revealing the very different functionality of the two building blocks.