RE5Co4Si14 (RE = Ho, Er, Tm, Yb):  Silicides Grown from Ga Flux Showing Exceptional Resistance to Chemical and Thermal Attack

The compounds RE5Co4Si14 (RE = Ho, Er, Tm, and Yb) have been synthesized from a Ga flux and characterized by X-ray diffraction. They can also be made by direct combination of the elements with arc melt alloying. All crystallize in the Lu5Co4Si14 structure type in the monoclinic space group P21/c with lattice parameters: a = 12.3765(15) Å, b = 7.8142(9) Å, c = 7.7330(9) Å, β = 98.867(2)°; a = 12.337(2) Å, b = 7.7990(14) Å, c = 7.7144(15) Å, β = 98.85(3)°; a = 12.3140(16) Å, b = 7.778(1) Å, c = 7.705(1) Å, β = 98.815(2)°; and a = 12.255(3) Å, b = 7.7537(16) Å, c = 7.6730(15) Å, β = 98.95(3)° for Ho5Co4Si14, Er5Co4Si14, Tm5Co4Si14, and Yb5Co4Si14, respectively. The compounds are composed of a dense Si/Co framework that is assembled from [Co4Si10] slabs and [Si4] zigzag chains. Crystals of the title compounds proved to be remarkably resistant to thermal oxidative attack (up to 1000 °C) as well as chemical attack from concentrated mineral acids and bases. The origin of this behavior can be traced to the details of the crystal structure and the Si-rich nature of the crystal framework.