Magnetic properties of dilute MgCe alloys

Abstract

The cerium + oxygen system has been studied by investigating the vaporization behavior of the sesquioxide phase as a function of temperature and composition employing mass effusion and mass-spectrometric techniques. The congruently vaporizing composition of the sesquioxide phase is slightly super-stoichiometric, varying from CeO1.51 at 2000 K to CeO1.53 at 2300 K. The composition of the lower phase boundary varies from near CeO1.50 at 1600 K to CeO1.34 at 2000 K. The partial pressures of CeO(g) and CeO2(g) over the congruently vaporizing sesquioxide were measured over the temperature range 1825 to 2320 K in the presence of both tungsten and rhenium and the partial molar enthalpies were determined for the composition CeO1.52. The partial pressures of Ce(g) and CeO(g) over the liquid metal + sesquioxide system were measured over the temperature range 1550 to 2040 K. The equilibrium constants for the isomolecular exchange reactions: Ce(g) + LaO(g) = CeO(g) + La(g) and Ce(g) + YO(g) = CeO(g) + Y(g), were evaluated as a function of temperature. The following thermochemical quantities were determined: ΔGfo(CeO,g)/calmol−1=−37360−10.80T/K,andΔGfo(CeO2,g)/calmol−1=−131350+6.98T/K.The standard Gibbs energy of formation of the sesquioxide at the lower phase boundary was calculated as a function of temperature; a calculated value of − 281.1 kcal mol−1, corresponding to the composition CeO1.40, is about 18 kcal mol−1 less negative than that of the stoichiometric sesquioxide CeO1.5.