  Ternary silicides MI(MII0.5, Si0.5)2 (MI=Sr and Ba, MII=Al and Ga) were
prepared by Ar arc melting. Powder X-ray diffraction indicates that they have
the AlB2-type structure, in which Si and MII atoms are arranged in honeycomb
layers and MI atoms are intercalated between them. Electrical resistivity and
dc magnetization measurements revealed that Sr(Al0.5, Si0.5)2 is
superconductive, with a critical temperature for superconductivity (TC) of 4.2
K, while Ba(Al0.5, Si0.5)2 is not at temperatures ranging above 2.0 K.
Sr(Ga0.5, Si0.5)2 and Ba(Ga0.5, Si0.5)2 are also superconductors, with TCs of
5.1 and 3.3 K, respectively.
