ANO2

AnO2 is a general formula used for a family of actinide dioxides, where An stands for an actinide element such as uranium, plutonium, americium, or curium. The most prominent members are UO2 and PuO2. These compounds crystallize in the fluorite structure, with the actinide ions forming a face-centered cubic lattice and oxide ions occupying the tetrahedral sites, giving the stoichiometry AnO2. The nominal oxidation state is +4 for the actinide.

The composition can deviate from strict stoichiometry under certain conditions. Non-stoichiometric variants include AnO2+x, with oxygen interstitials, or AnO2−y, with oxygen vacancies. Such defects influence properties like electrical conductivity, diffusion, and phase stability. Lattice parameters and bonding characteristics vary across the actinide series, reflecting differences in ionic radii and electronic structure.

Physical properties of AnO2 compounds typically include high melting points and high densities. They are generally insulating to semiconducting, with electronic behavior strongly affected by 5f electron localization and defects. Some examples show magnetic ordering at low temperatures (for instance, UO2 is antiferromagnetic below about 30 K), while others (such as PuO2) are non-magnetic in the bulk. Thermal and radiation effects can influence phase stability and defect populations.

Applications center on nuclear materials science. UO2 is the standard fuel in many light-water reactors, and PuO2 is used in mixed-oxide (MOX) fuels and various research contexts. Other actinide dioxides are studied for fundamental properties, actinide cycling, and potential future fuel concepts.

Safety considerations are significant, as actinide dioxides are highly radiotoxic and require specialized handling, containment, and waste management practices.