Density-Functional Study Of The La2zr2o7 (001) And (011) Surfaces And Bulk

Lanthanum zirconate (La2Zr2O7, LZ)-based compounds are of interest for their catalytic activity. Accordingly, the low index (001) and (011) surfaces of LZ are studied at the level of density-functional theory, representing the first theoretical attempt to characterize the surfaces of this compound. All possible surface terminations of the (001) and (011) surfaces formed by cleaving a perfect crystal are considered. These surfaces are termed ideal. In addition, judiciously chosen defective (001) and (011) surfaces are examined. The expression for the free energy of a LZ surface is derived, and it is a function only of temperature and oxygen gas partial pressure for all surfaces considered. Both surface energies and surface free energies are computed. A defective (001) surface is shown to be thermodynamically preferred to any ideal (001) surface over a wide range of temperatures and oxygen gas partial pressures. Thus, the first evidence is provided for a (001) surface that is defective or otherwise not ideal, for example, reconstructed. Results are discussed in the context of a proposed comparison of predicted relative crystallite thicknesses perpendicular to (001) and (011) surfaces to experimental results. However, the experimental results still need to be obtained to permit this comparison.