Forming Platinide Phases under Pressure in the Cs–Pt System

Abstract

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.

High-Temperature Oxidation-Resistance of Rare-Earth Transition Metal Silicides: Crystal Chemistry Insights from the Sc–Os–Si System

“…The MgZn 2 -type structure is a classic representation of the C14 Laves phase (Figure 3a) with two distinct structural units: trigonal-bipyramidal Zn units that share vertices extending into the c-axis, and Mg centering a face-sharing Friauf truncated tetrahedron. 55,56 The literature indicates that Sc can occupy the Mg site and Os can occupy the Zn sites forming ScOs 2 . Prior research has also demonstrated that the Zn sites can accommodate mixed occupancy of transition metal atoms and silicon atoms, resulting in the ordered variant Mg 2 Cu 3 Si-type structure.…”