Atomic ordering in the Laves phases L1 V(Co1–xSix)2 (x = 0.43 and 0.56)

Abstract

Abstract The synthesis, phase relations, and crystal structures of two truly ternary, partially ordered Laves phases occurring in the V—Co—Si system are reported. The phases termed L1 V(Co1–xSix)2 are found in two distinct phase fields next to TiMnSi-type VCoSi. This so-called E-phase emerges in the centre of the miscibility gap which separates the Co- and Si-rich Laves phase fields. Both fields accommodate several structurally distinct L-phases. The L1-phases V(Co1–xSix)2 (x = 0.43 and 0.56) crystallise in √3a × √3a superstructures of the hexagonal MgZn2 structure type. A rigorous symmetry-based analysis reveals that, at the given compositions, this type of superstructure affords sufficient structural degrees of freedom for ordering of Co and Si atoms on 4 different sites in a manner that enables tuning of hetero-atomic Co—Si interactions to an optimum.