Targeting complex plutonium oxides by combining crystal chemical reasoning with density-functional theory calculations: the quaternary plutonium oxide Cs2PuSi6O15

Abstract

The stability of the novel Pu(IV) silicate, Cs₂PuSi₆O₁₅, was predicted from a combination of crystal chemical reasoning and DFT calculations and confirmed by its synthesis via flux crystal growth. Formation enthalpies of the A₂MSi₆O₁₅ (A = Na–Cs; M = Ce, Th, U–Pu) compositional family were calculated and indicated the Cs-containing phases should preferentially form in the Cmc2₁ structure type, consistent with previous experimental findings and the novel phases produced in this work, Cs₂PuSi₆O₁₅ and Cs₂CeSi₆O₁₅. The formation enthalpies of a second set of compositions, A₂MSi₃O₉, were also calculated and a comparison between the two compositional families correctly predicted A₂MSi₆O₁₅ to be on average more stable than A₂MSi₃O₉.