Thermodynamic Properties of Platinum-rich Intermetallics in the Pt–Gd System

抄録

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_0.50Pt_0.50:ΔG^M=−104000+0.80 T(±380) J/mol