Forming Platinide Phases under Pressure in the Cs–Pt System
2022
Arrieta, Roy | Brgoch, Jakoah
A series of platinide-containing phases were identified as thermodynamically favorable compounds at high pressure (10 GPa) using an unbiased automatic crystal structure searching method. Density functional theory paired with a particle swarm optimization (PSO) algorithm supports the formation of Cs₂Pt at ambient pressure, agreeing with experimental observations. The calculations then revealed that applying 10 GPa of pressure should result in three new phases: Cs₂Pt with the Fe₂P-type structure (space group P6̅2m; No. 189), Cs₂Pt₃ (space group Cmm2; No. 38), and CsPt₃ (space group C2/m; No. 12). Subsequent hybrid electronic structure calculations showed that Cs₂Pt is a semiconductor with the Fermi level falling in a band gap of 2.18 eV, whereas the Fermi level for Cs₂Pt₃ and CsPt₃ falls into a pseudogap, suggesting a metallic character. Examining the chemical bonding in the Cs-rich phase (Cs₂Pt) indicated that Cs–Pt ionic interactions dominate this structure, while Pt–Pt interactions are primary interactions in Pt-rich phases (Cs₂Pt₃ and CsPt₃). Interestingly, the ambient pressure phase and all three high-pressure phases exhibit unusual oxidation states on transition-metal atoms. The Pt charge is approximated to approach −1 due to charge transfer between Cs and Pt, as illustrated by Bader’s QM-AIM charge analysis and electron localization function (ELF) calculations. These results support the presence of a rare pressure-stabilized platinide anion.
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