Thermodynamic properties of platinum-rich intermetallics in the Pt-Gd system

Abstract

Phase relations in the Pt-GdPt portion of the system have been determined at 1100 K by X-ray and microscopic examination of quenched samples equilibrated for 610 ks. Five compounds have been identified; GdPt₅, `GdPt₃', GdPt₂, Gd₃Pt₄ and GdPt. The phase GdPt3 with AuCu₃ type structure has not been reported earlier. The compound GdPt₃ is nonstoichiometric with a homogeneity range extending from 23 to 28 mol% Gd. The phase GdPt₂ has a narrower nonstoichiometric range varying from 32 to 33 mol% Gd. The relative partial Gibbs' energy of Gd in the two-phase fields has been determined in the temperature range 925-1125 K using solid state galvanic cells incorporating single crystal CaF₂ as the solid electrolyte and an equimolar mixture of Gd + GdF₃ as the reference electrode. The Gibbs' energy formation of the intermetallic phases per mol has been derived from these measurements: Gd_0.17Pt_0.83:ΔG^M = -60650+1.30 T(±80) J/mol Gd_0.23Pt_0.77:ΔG^M = -78220+1.81 T(±180) J/mol Gd_0.28Pt_0.72:ΔG^M = -91686+2.077 T(±290) J/mol Gd_0.32Pt_0.68:ΔG^M = -94750-2.53 T(±300) J/mol Gd_0.33Pt_0.67:ΔG^M = -96135-2.11 T(±310) J/mol Gd_0.43Pt_0.57:ΔG^M = -103575-1.31 T(±360) J/mol Gd_0.50Pt0.50:ΔG^M = -104000+0.80 T(±380) J/mol