Silicide
A
silicide is a compound that has silicon with more electropositive elements. Silicon is more electropositive than carbon. Silicides are structurally closer to borides than to carbides. Similar to borides and carbides, the composition of silicides cannot be easily specified as covalent molecules. The chemical bonds in silicides range from conductive metal-like structures to covalent or ionic. Silicides of all non-transition metals, with exception of beryllium, have been described. Mercury, thallium, bismuth, and lead are nonmiscible with liquid silicon. Silicon atoms in silicides can have many possible organizations: ▪ Isolated silicon atoms: electrically conductive Cu5Si, 3Si, Fe3Si, Mn3Si, and nonconductive 2Si, 2Si ▪ Si2 pairs: U3Si2, Hf and Th silicides ▪ Si4 tetrahedra: KSi, RbSi, CsSi ▪ Sin chains: USi, Si, CaSi, SrSi, YSi ▪ Planar hexagonal graphite-like Si layers: β-USi2, silicides of other lanthanoids and actinoids ▪ Corrugated hexagonal Si layers: CaSi2 ▪ Open three-dimensional Si skeletons: SrSi2, ThSi2, α-USi2 A silicide prepared by a self-aligned process is called a salicide.