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.

AEAl4−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 as PowerPoint slide