Modeling the thermochemical behavior of AmO2−x

A thermochemical representation of the fluorite structure AmO2−x phase was developed using the compound energy formalism approach assuming constituents of (Am4+)1(O2−)2, (Am4+)1(Va)2, (Am3+)1(O2−)2, and (Am3+)1(Va)2. The Gibbs free energies for the constituents and a set of interaction parameters were determined using reported oxygen potential–temperature–composition data. A good fit to the experimental information was obtained which well-reproduces the behavior. The representation is also in a format that will allow incorporation of other dissolved metals and thus will be useful in generating multi-component compound energy formalism representations for complex oxide nuclear fuel and waste systems. A full assessment relating the fluorite structure phase to the phase equilibria for Am–O, however, must await adequate data for the remainder of the system.