Thermodynamic and phase relation study of the Ni - Ge - O system in the solid state

Abstract In order to clarify the phase relation in the Ni–Ge–O system and to obtain the activity of germanium in solid Ni–Ge alloys, phase equilibrium experiments and EMF measurements with a zirconia-based solid electrolyte are performed from 950 to 1100 K. The results are as follows: 1) Ni-rich alloys with less than 24.0 at.% Ge cannot coexist with GeO2 (tetragonal). 2) In solid Ni–Ge alloys with 24.0–44.7 at.% Ge, the activity of Ge changes sharply in the Ni5Ge3 phase region and the temperature dependence of the activity is very small. 3) Equilibrium oxygen partial pressures are obtained in the whole composition range in the ternary Ni–Ge–O system at 1050 K.