The ternary intermetallic compounds $MAB=\text{CaAlSi}$, SrAlSi, BaAlSi, CaGaSi, SrGaSi, BaGaSi, SrAlGe, BaAlGe, CaGaGe, SrGaGe, BaGaGe, BaInGe, BaAlSn, CaGaSn, SrGaSn, and BaGaSn have been prepared by arc-melting stoichiometric elemental mixtures and structurally characterized by a combination of x-ray powder and electron diffraction. They crystallize as variants of the simple hexagonal ${\text{AlB}}_2$ structure type where trivalent and tetravalent $A$- and $B$-type atoms, respectively, form commonly a planar hexagon layer, and structural variations arise from $A/B$ ordering and/or puckering of hexagon layers. The silicides $\left(B=\text{Si}\right)$ were previously investigated for their superconducting properties. By dc magnetization measurements it is demonstrated that also the germanides SrAlGe, BaAlGe, SrGaGe, and BaGaGe and the stannide BaAlSn are superconductors above 2 K.

• Received 8 April 2009

DOI:https://doi.org/10.1103/PhysRevB.80.064514