From simple to complex crystal chemistry in the RE−Au−Tt systems (RE = La, Ce, Pr, Nd, Ho; Tt = Ge, Sn, 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, Ho; Tt = Ge, Sn, 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 unreported eight compounds ranging from the simple NaTl-type compounds La1.5Au2Pb0.5, Nd2-xAu2Pbx, and Ho2-xAu2Snx, 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 revealed that a combination of Fermi surface-Brillouin zone interactions, electrostatic interactions, and delocalized metallic bonding 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.