Crystal structure of hafnium palladium gallium, HfPdGa

ZrNiAl-type gallides with pronounced metal-metal bonding, and the dimorphism of ScPdGa

The ZrNiAl-type (space group P6̅2m) gallides TIrGa (T=Zr, Nb, Hf, Ta), ZrNiGa and ScPdGa were obtained by arc-melting of the elements, followed by annealing in sealed silica tubes. The samples have been characterized through their Guinier powder patterns. The structures of ZrNiGa, NbIr1.08Ga0.92 and TaIr1.10Ga0.90 were refined from single-crystal X-ray diffractometer data. Refinements of the occupancy parameters indicate the formation of solid solutions for the niobium and the tantalum compound. Within the huge family of ZrNiAl-type phases, NbIr1.08Ga0.92 and TaIr1.10Ga0.90 have the smallest c/a ratios; however, no structural distortions or superstructure formation have been observed. Electronic structure calculations were exemplarily carried out for NbIrGa, substantiating the dominance of the Ir–Ga and Nb–Ir bonding interactions. Temperature dependent magnetic susceptibility measurements of LT-ScPdGa, ZrIrGa, NbIrGa and HfIrGa have shown Pauli paramagnetism. ScPdGa is dimorphic with an orthorhombic TiNiSi-type high-temperature modification (arc-melting and quenching; space group Pnma) which transforms to the hexagonal ZrNiAl-type low-temperature modification upon annealing at 1023 K. Both structures were refined from single-crystal X-ray diffractometer data. HT-ScPdGa exclusively shows Pd–Ga bonding within the three-dimensional [PdGa] polyanionic network, while additional weak Pd–Pd and Ga–Ga interactions occur in LT-ScPdGa.