Ternary transition metal gallides with TiNiSi, ZrBeSi and MgZn${}_2$-type structure

A series of ternary transition metal gallides around the equiatomic composition have been synthesized from the elements by arc-melting and subsequent annealing. The compounds crystallize with site occupancy variants of the hexagonal Laves phase MgZn${}_2$, with the hexagonal ZrBeSi or the orthorhombic TiNiSi type. All samples have been characterized on the basis of their lattice parameters, determined by X-ray powder diffraction (Guinier technique). The structures of NbCr${}_{1.58}$Ga${}_{0.42}$ and NbFe${}_{1.51}$Ga${}_{0.49}$ (MgZn${}_2$ type, P6${}_3$/mmc), NbRhGa (ZrBeSi type, P6${}_3$/mmc), and ScNiGa, ScPtGa and ScAuGa (TiNiSi type, Pnma) were refined from single crystal X-ray diffractometer data. The ScPtGa and ScAuGa crystals showed trilling formation. Mixed site occupancies were only observed in the Laves phases while all other crystals were well ordered. A striking structural motif of NbRhGa is the formation of niobium chains (264 pm Nb-Nb) along the c axis. Several gallides were magnetically characterized. They are Pauli paramagnets. The two crystallographically independent iron sites in the Laves phase TaFeGa could be distinguished in the ${}^{57}$Fe Mössbauer spectrum. The isomer shifts of 0.06(3) (Fe1) and -0.02(3) (Fe2) mm s${}^{\text{â}\text{ˆ}\text{’}1}$ indicate metallic iron.