Predicted structure and stability of A4B3O12 -phase compositions

A combination of atomistic simulation techniques has been employed to predict ordered structures for a series of
A₄B₃O₁₂- phase compounds, where A is a 3+ cation ranging in size from Sc³⁺to Ho³⁺ and B is a 4+cation ranging from Ti⁴⁺ to Zr⁴⁺. Experimentally, a fully ordered cation structure has yet to be resolved for any of these compounds. Monte Carlo energy-minimization calculations using short-range pair potentials identified three low-energy arrangements of A³⁺and B⁴⁺cations. The details of these three structures were analyzed with the layer motif method. To quantitatively determine the -phase structure of each composition, the three configurations were reevaluated with density-functional theory. We also used special quasirandom structuresto compare the ordered low-energy configurations to cation disorder. For all compositions considered, we find that at least one of the three ordered structures is lower in energy than the disordered structure, suggesting the thermodynamic stability of an ordered phase. Of the three ordered structures identified by this approach, one has not been identified previously in the literature for any composition. In addition, we discuss the stability of -phase compounds with respect to other ABO_{4 x} fluorite-derivative compositions and predict the structure of compositions for which none has been reported.