Adaptation of the BaAl4 Type to Small Cations: The Case of NaGa4

Abstract Single‐phase NaGa 4 samples were prepared by annealing stoichiometric element mixtures at 200 °C, 300 °C, and 450 °C in closed tantalum ampoules. No compositional homogeneity range was detected. While single crystals annealed at 200 °C feature a fully ordered crystal structure, a crystal annealed at 300 °C reveals a defect with mutual exchange of Na atoms and Ga 2 dumbbells. The structure motif caused by the violation of translational symmetry resembles the CeMg 2 Si 2 type of structure. The NaGa 4 structure constitutes a branch of the BaAl 4 type distinguished by a notably high c / a ratio (space group I 4/ mmm ; a =4.2261(1) Å, c =11.2633(6) Å, c / a =2.67). This distortion enables the adaption of the BaAl 4 ‐type to small cations, when the further shortening of the apical–apical distance d (Ga–Ga) is not possible any more. Therefore, NaGa 4 offers an adaption alternative to the monoclinic distortion observed in CaGa 4 and YbGa 4 . Conductivity measurements validate the metallic behavior anticipated by NMR measurements in earlier studies.