Ca2Pd3Ge, a new fully ordered ternary Laves phase structure

The title compound, Ca2Pd3Ge, was prepared as a part of a systematic investigation of the Ca–Pd–Ge ternary phase diagram. The structure was determined and refined from single-crystal X-ray diffraction data. It is a new fully ordered ternary Laves phase with the space group R-3m, Z=3, a=5.6191 (5) Å, c=12.1674 (7) Å, wR2=0.054 (all data) and is isostructural to Mg2Ni3Si (Noréus et al., 1985 [17]) but due to the larger size of all elements in Ca2Pd3Ge, the cell axes are approximately 10% longer. The compound may formally be considered as a Zintl compound, with [Pd3Ge]4− forming a poly-anionic network and divalent Ca cations located in truncated tetrahedral interstices. The electronic structure and chemical bonding of Ca2Pd3Ge is discussed in terms of LMTO band structure calculations and compared with CaPd2 (MgCu2-type).

The title compound, Ca2Pd3Ge is a new fully ordered ternary Laves phase which may formally be considered as a Zintl compound, with [Pd3Ge]4− forming a poly-anionic network and divalent Ca cations located in truncated tetrahedral interstices. The structure is composed of Kagomé net layers, consisting of Pd atoms only, which are stacked in an ABC sequence. Band structure calculations show that the Fermi level is located at a local minimum of the DOS (pseudo-gap) indicating that the charge is roughly optimized in the structure.Figure optionsDownload as PowerPoint slideHighlights
► Site specific segregation in a Laves phase that is also a Zintl phase.
► Pseudo-gap at the Fermi level in a Laves phase.
► Distorted Frank–Kasper polyhedron.