Molecular Dynamics Studies of Ordered and Disordered Lanthanum Cerate: Thermodynamic Stability, Heat Capacity, and Oxygen Diffusivity

Oxides with the formula A 2 B 2 O 7 may crystallize either as ordered pyrochlores or as oxygen‐deficient defect fluorites. Lanthanum cerate is a material for which both structures have been proposed in the literature. In this study, molecular dynamics (MD) simulations with many‐body potentials are used to examine as a function of temperature the relative stability of the two phases, as well as of intermediate phases with varying degrees of cation disorder . The simulations also yield as a function of and the isobaric heat capacity and the oxygen tracer diffusivity . Taking the calculated cell energies and considering in addition configurational entropy, we find that defect fluorite structures are thermodynamically favored for lanthanum cerate. data for ordered structures exhibit an anomalous increase at higher temperatures, indicative of anti‐Frenkel disorder. Converting calculated oxygen tracer diffusion coefficients into ionic conductivities and comparing with reported experimental data, we find good agreement, especially concerning the activation enthalpy, with data for the defect fluorite structure.