Ayako Kushida, Teruyuki Ikeda Hiroshi Numakura and Masahiro Koiwa
Department of Materials Science and Engineering, Kyoto University, Kyoto 606--8501
Thermodynamic activity of Ga in the L12--ordered intermetallic phase Ni3Ga has been determined by measuring the electromotive force of a galvanic cell with zirconia solid electrolyte,
Ni--Ga, Ga2O3|ZrO2(+Y2O3)|Ga, Ga2O3
in the temperature range of 1050--1350 K for six compositions. The activity of Ga varies with composition most steeply at the stoichiometry composition (25%Ga). The dependence on composition is more pronounced at low temperatures. The effective pair interaction energy has been determined to be 9.75±0.19 kJ/mol by applying a thermodynamic model based on Bragg--Williams approximation (Ikeda et al., Acta. Mater., 46(1998), 6605--6613). The thermodynamic factor in diffusion has been derived from the composition dependence of the thermodynamic activity.
(Received December 13, 1999; In Final Form February 16, 2000)
intermetallic compound, solid--electrolyte cell, electromotive--force method, composition--dependence of thermodynamic activity, interatomic interaction energy, thermodynamic factor in diffusion
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