Oxygen potential measurements of fluorite-type Zr0.5Pu0.5O2−y by EMF method

The dependence of the oxygen potentials (g(O2)) on oxygen non-stoichiometry (y) and temperature (T) of oxygen-deficient fluorite-type (F-type) plutonium zirconate Zr0.5Pu0.5O2−y has been elucidated by electromotive force (EMF) measurements: (Pt) air ∣Zr(Ca)O2−x∣ Zr0.5Pu0.5O2−y (Pt). The y value of Zr0.5Pu0.5O2−y was varied at 1078 K over 0 ⩽ y < 0.10 and the isothermal g(O2) were measured by applying the coulomb titration method. The temperature dependence of the g(O2) was also measured for each y by performing the temperature scan down to 793 K (793 ⩽ T ⩽ 1078 K). It was found that the g(O2) decreased from ∼0 to −480 kJ/mol with increasing y from ∼0 to 0.1 at 1078 K and that the isothermal g(O2) as a function of y exhibited a simple concave curve. The powder XRD results showed that Zr0.5Pu0.5O2−y maintained its single F-type structure over 0 ⩽ y < 0.10 at 1078 K. The lattice parameters (a0) in this system were found to increase almost linearly with y over 0 ⩽ y < 0.10.