Metal Flux Growth of Complex Alkaline Earth/Rare Earth Metal Silicides with a Homologous Series of Metal Phosphide Structure Types

Three new metal silicides
were grown as competing products from
reactions of silicon with barium and ytterbium in Mg/Al flux; the
dominant product is determined by the heating profile as well as by
the reactant ratio. The compounds Ba2Yb0.88Mg11.12Si7, Ba5Yb2.26Mg16.73Si12, and Ba20Yb4.7Mg61.3Si43 all exhibit hexagonal crystal structures
that are analogous to those of ternary metal phosphides (Zr2Ni12P7, Ho5Ni19P12, and Ho20Ni66P43, respectively).
The structures feature building blocks composed of silicon anions
surrounded by nine metal cations; these tricapped trigonal prismatic
Si@(Mg/Yb/Ba)9 polyhedra share faces to form the overall
structures. Magnetic susceptibility measurements show Pauli paramagnetic
behavior for all three compounds, indicating the ytterbium is divalent.
The silicides have a 2:1 ratio of metal cations to silicide anions
and are therefore charge-balanced. This should result in semiconducting
or semimetallic behavior; the latter is supported by electronic structure
calculations. The formation of these compounds indicates that a large
family of complex silicides is accessible from reactions of silicon
and divalent metals (Ca, Sr, Ba, Eu, Yb) in magnesium-based fluxes.