Thermodynamic properties of Pt₅La, Pt₅Ce, Pt₅Pr, Pt₅Tb and Pt₅ Tm intermetallics

Abstract

The Gibbs’ energies of formation of Pt₅La, Pt₅Ce, Pt₅Pr, Pt₅Tb and Pt₅ Tm intermetallic compounds have been determined in the temperature range 870–1100 K using the solid state cell: Ta,M+MF₃/CaF₂/Pt₅M+Pt+MF₃,Ta The reversible emf of the cell is directly related to the Gibbs’ energy of formation of the Pt₅M compound. The results can be summarized by the equations: ΔG_f∘Pt₅La=−373,150+6⋅60T±300Jmol⁻¹ ΔG_f∘Pt₅Ce=−367,070+5⋅79T±300Jmol⁻¹ ΔG_f∘Pt₅Pr=−370,540+4⋅69T±300Jmol⁻¹ ΔG_f∘Pt₅Tb=−372,280+4⋅11T±300Jmol⁻¹ ΔG_f∘Pt₅Tm=−368,230+4⋅89T±300Jmol⁻¹ relative to the low temperature allotropic form of the lanthanide element and solid platinum as standard states The enthalpies of formation of all the Pt5M intermetallic compounds obtained in this study are in good agreement with Miedema’s model. The experimental values are more negative than those calculated using the model. The variation of the thermodynamic properties of Pt₅M compounds with atomic number of the lanthanide element is discussed in relation to valence state and molar volume.