PuO2x

PuO2x is a non-stoichiometric form of plutonium oxide in which the oxygen content deviates from the ideal PuO2 composition. In the literature, PuO2+x (or PuO2−δ) is used to denote solid solutions where the amount of oxygen can be tuned around the PuO2 baseline. The variable x (or δ) indicates either excess oxygen (x > 0) or an oxygen deficiency (δ > 0) relative to PuO2.

Crystal structure and defects are central to PuO2x. PuO2 itself adopts a fluorite-type structure with plutonium atoms in a face-centered cubic arrangement and oxygen occupying tetrahedral sites. Non-stoichiometry is accommodated by point defects in the oxygen sublattice, including oxygen interstitials and vacancies. These defects influence lattice parameters, thermodynamic stability, and electronic structure. Under oxidizing conditions, oxygen interstitials form PuO2+x, potentially stabilizing higher plutonium oxidation states; under reducing conditions, oxygen vacancies form PuO2−δ. The fluorite framework generally remains intact over a wide range of x, though large deviations can lead to structural changes and phase transitions.

Occurrence and relevance are closely tied to processing and storage of plutonium materials. PuO2+x can arise during high-temperature annealing in oxygen, corrosion in air, or long-term storage under varying oxygen potentials. The degree of non-stoichiometry affects properties such as diffusion rates of oxygen and fission products, electrical conductivity, and radiation stability. In nuclear science and actinide chemistry, PuO2x informs models of fuel performance, waste immobilization, and redox behavior of plutonium oxides.

Safety and handling considerations are important, as plutonium oxides are radioactive and require licensed facilities and specific containment protocols.