Pt-Driven Stable and Metastable Ternary Compounds with Tunable Partial Flat Bands in Immiscible Si–Sn System

A combined machine learning approach and first-principles calculations are employed to efficiently explore energetically favorable ternary compounds involving Pt and an immiscible Si-Sn pair of elements. We predict two stable Pt-Si-Sn ternary compounds (Pt₂Si₂Sn and Pt₈SiSn₂) and reproduce the experimentally synthesized Pt₅SiSn. The crystal structures of Pt₅SiSn and Pt₈SiSn₂ are composed of a SiPt₈ cube and SnPt₁₂ cuboctahedron. Based on these structural motifs, we design a series of Pt-Si-Sn ternary compounds that contain SiPt₈ and SnPt₁₂ units and discover some stable and metastable compounds. Partial flat bands near the Fermi level appear in these compounds, and the positions of partial flat bands move upward with increasing the Pt content. The partial flat bands are dominated by Pt atoms. These Pt-Si-Sn ternary compounds provide a platform to study flat band-related properties. Our results open a way to design new compounds in the ternary system.