Thermodynamic Properties of Holmium Germanides

Abstract

The Gibbs free energy, enthalpy, and entropy for formation of holmium germanides HoGe_3–x (HoGe_2,7), HoGe_2–y (HoGe_1,8), HoGe_2–a (HoGe_1,7), HoGe_2–b (HoGe_1,5), Ho₃Ge₄, HoGe, Ho₁₁Ge₁₀, Ho₅Ge₄, and Ho₅Ge₃ are determined by measuring electromotive forces in the temperature range 770–970 K. The negative values of the Gibbs free energy and enthalpy of formation increase with the holmium content in a compound and reach extreme values for Ho₅Ge₃ which has the highest melting point and is the only congruently melting compound in the Ho–Ge system. The thermodynamic properties for formation of solid and liquid alloys of holmium with germanium are compared. Like the solid alloys, the highest enthalpy of mixing is in the range of Ho-rich compositions. Standard enthalpy and entropy of formation of HoGe_1,5, HoGe, and Ho₅Ge₃ are calculated.