First-principles computational study of defect clustering in solid solutions of ThO$_{2}$ with trivalent oxides

摘要

The energetics of mixing and defect ordering in solid solutions offluorite-structured ThO$_{2}$ with oxides of trivalent cations (Sc, In, Y, Nd,La) are investigated by electronic density-functional-theory (DFT). Through DFTcalculations of structures enumerated by lattice-algebra techniques, weidentify the lowest-energy patterns for defect clustering for four separatedopant concentrations. The most stable structures are characterized by arepulsive interaction between nearest-neighbor vacancies on the oxygensublattice. The enthalpies of formation with respect to constituent oxides arepositive for all dopants considered, and show a tendency to decrease inmagnitude as the size and electronegativity of the trivalent dopant decrease.Due to the small positive formation enthalpies and low oxygen-vacancy bindingenergy with La dopants, La$_{2}$O$_{3}$-ThO$_{2}$ solid solutions are predictedto have relatively high ionic conductivities relative to those for the otheraliovalent dopants considered. Our results are compared with those for the morewidely studied ZrO$_{2}$ and CeO$_{2}$ fluorite-structured solid solutions withtrivalent cations.