The Gd₁₄Ag₅₁ structure type and its relation to some complex amalgam structures

Highlights: • The Gd₁₄Ag₅₁ structure type has been revisited on the basis of single crystal diffraction data. • Symmetry analysis from electron density and TEM shows the space group P6/m to be true. • Gd₁₄Ag₅₁ shows good metallic behaviour. • Structure relations to alkali, alkaline-earth and rare-earth metal amalgams can be established. • Complexity values for the RE₁₄Ag₅₁ structure family were calculated. - Abstract: A plethora of binary and ternary intermetallic compounds has been assigned to the Gd₁₄Ag₅₁ structure type, crystallising in the hexagonal system (space group P6/m, a = 1264.30(18) pm, c = 933.58(11) pm for Gd₁₄Ag₅₁). Starting in the late 1960s, much work has been invested in the structural elucidation of these crystal structures. However, reliable single crystal data are scarce, and most structure type assignments have been performed merely on the basis of powder data. We have redetermined four representatives of the binary RE₁₄Ag₅₁ structure type (RE = Y, Ce, Gd, Tb) with modern high-precision single crystal X-ray methods. The assignment of the Gd₁₄Ag₅₁ structure type to space group P6/m was additionally verified by careful analysis of high resolution transmission electron micrographs. We emphasise the close relation of the Gd₁₄Ag₅₁ structure type to the structures of some recently described amalgams of similar composition focussing on disorder phenomena and structural complexity. Furthermore, we provide detailed information on synthesis as well as electrical and magnetic properties for Gd₁₄Ag₅₁, the parent compound of this structure family