Synthesis, structural characterization and properties of SrAl4−xGex, BaAl4−xGex, and EuAl4−xGex (x≈0.3–0.4)—Rare examples of electron-rich phases with the BaAl4 structure type

•Three BaAl4-type ternary aluminum germanides have been synthesized with Eu, Sr and Ba.•Eu, Sr and Ba cations have no apparent influence on the solubility of Ge.•The Ge atoms substitute Al on one of two framework sites, thereby strengthening the interactions between the cations and the polyanionic framework.

Three solid solutions with the general formula AEAl4−xGex (AE=Eu, Sr, Ba; 0.32(1)≤x≤0.41(1)) have been synthesized via the aluminum self-flux method, and their crystal structures have been established from powder and single-crystal X-ray diffraction. They are isotypic and crystallize with the well-known BaAl4 structure type, adopted by the three AEAl4 end members. In all structures, Ge substitutes Al only at the 4e Wyckoff site. Results from X-rays photoelectron spectroscopy on EuAl4−xGex and EuAl4 indicate that the interactions between the Eu2+ cations and the polyanionic framework are enhanced in the Ge-doped structure, despite the slightly elevated Fermi level. Magnetic susceptibility measurements confirm the local moment magnetism, expected for the [Xe]4f7 electronic configuration of Eu2+ and suggest strong ferromagnetic interactions at cryogenic temperatures. Resistivity data from single-crystalline samples show differences between the title compounds, implying different bonding characteristics despite the close Debye temperatures. A brief discussion on the observed electron count and homogeneity ranges for AEAl4−xGex (AE=Eu, Sr, Ba) is also presented.

Graphical abstractAEAl4−xGex (AE=Eu, Sr, Ba; 0.32(1)≤x≤0.41(1)), three “electron-rich” phases with BaAl4 structure type have been synthesized and characterized.Figure optionsDownload full-size imageDownload as PowerPoint slide