Evolutionary Search for Novel Thorium Borides toward Advanced Nuclear Fuels

Thorium (Th)-based fuels are considered as promising candidates for generation-IV reactors. To explore potential thorium boride (ThxBy) structures and to obtain physical properties of these thorium borides, in our work, a variable-composition evolutionary algorithm prediction method implemented in the Universal Structure Predictor: Evolutionary Xtallography code was adopted to search stable binary compounds in the Th–B system. Six stable and metastable Th–B binaries with different chemical compositions were predicted, in which three hitherto-unknown phases ThB2, Th3B4, and ThB were discovered. The electronic, mechanical, and thermal properties of these thorium borides were studied in detail based on the first-principles method. ThB is the only ionic compound, and the other compounds exhibit metallic and covalent properties. All the thorium borides except for Th3B4 exhibit excellent thermal conductivity. In addition, ThB4 and ThB12 have outstanding mechanical properties. ThB2, ThB4, and ThB12 are expected to be promising candidates for new nuclear fuels due to their appropriate mechanical and thermal properties.