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 Lu₅Co₄Si₁₄structure 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.