High Pressure Cotunnite Structure of ThO2: A DFT Study

Thorium dioxide (ThO2) is most commonly used nuclear fuel with UO2 and PuO2 in thermal breeder nuclear reactor. ThO2 has fluorite type structure at normal pressure, but at higher pressure it shows transition from fluorite type structure to cotunnite type structure. We have considered cotunnite type ThO2 structure to study the electronic and optical properties using first principles method. This high pressured ThO2 structure shows direct band gap of 3.43 eV. Density of states shows major contribution of 2p orbital in valence band while conduction band is dominated by 5f orbital near the Fermi energy level. Static dielectric constant and refractive index are found to be 2.86 and 1.67. Absorption spectra show absorption in UV region with a sharp peak at 5.67 eV.