Oxygen potential of solid solution Eu_yU_1-yO_2+x

The oxygen potential, ΔḠ_O2, of Eu_yU_1-yO_2+x solid solution was measured as a function of x value for y = 0.05 and 0.1 at 1000, 1100 and 1200°C using an electrobalance. With the addition of europium, a significant increase in ΔḠ_O2 was observed in the hypostoichiometric region, but its effect was almost the same for y = 0.05 and 0.1 in the hyperstoichiometric region. The O/M (M=Eu + U) ratio, which yields the steepest change of ΔḠ_O2, decreased with decreasing temperature in the range ca.1000-1400°C for y = 0.1, although this effect was not seen for y = 0.05. The temperature dependence of this decrease seemed to be enhanced as the y value increased. Both the partial molar entropy and enthalpy of oxygen (ΔS̄_O2 and ΔH̄_O2) for y = 0.1 solid solution showed sharp large peaks at O/M ratios slightly less than 2. Such peaks emerge as a result of the above decrease of the O/M ratio for steepest change of ΔḠ_O2, with decreasing temperature.