From simple to complex crystal chemistry in the RE–Au–Tt systems (RE = La, Ce, Pr, Nd; Tt = Ge, Pb)

Polar intermetallics are an intriguing class of compounds with complex relationships between composition and structure that are not fully understood. This work reports a systematic study of the underexplored ternary composition space RE–Au–Tt (RE = La, Ce, Pr, Nd; Tt = Ge, Pb) to expand our knowledge of the intriguing chemistry and diversity achievable with these metallic constituents. These composition spaces are particularly interesting because of the potential to find Au-bearing, highly polar intermetallic compounds. The elements were first reacted through arc welding under an inert atmosphere, followed by annealing at 850 °C. X-ray diffraction of the products identified seven unreported compounds ranging from the simple NaTl-type compounds La_1.5Au₂Pb_0.5 and Nd_2–xAu₂Pb_x to the more structurally complex La₅AuPb₃ in the Hf₅CuSn₃-type structure and Pu₃Pd₄-type RE₃Au₃Ge (RE = La, Ce, Pr, Nd). First-principles electronic structure calculations investigate the combination of Fermi surface–Brillouin zone interactions, electrostatic interactions, and delocalized metallic bonding that contributes to the formation of these phases. These calculations show that a mixture of electrostatic and metallic bonding plays a dominant role in these phases. The RE–Au–Tt composition space remains full of potential for discovering materials with relevant magnetic and quantum properties, provided the crystal chemistry can be comprehended.