Structural,electronic, stability and reduction properties of perovskite surfaces: The case of rhombohedral BaCeO3

The (100), (110) and (111) surfaces of rhombohedral phase BaCeO₃ perovskite with two kinds of surface terminations are investigated using a periodic DFT + U method. We show that the lowest energy for surface formation via crystal cutting (cleavage energy) corresponds to (100) terminations. Out of all studied terminations, only BaO(100) and BaCeO(110) are stable with respect to precipitation of oxide phases and metals in respective ranges of oxygen chemical potentials, whereas CeO2(100) termination is not stable with respect to CeO₂ precipitation for all temperatures and oxygen partial pressures. Analyzing the electronic properties of the surfaces, we have established that reduction of the cerium oxidation state occurs in response to the local stoichiometry (lack of surface oxygen's, etc.) rather than as a result of breaking of cerium–oxygen bonds and formation of under-coordinated cerium ions. This equally applies to cerium reduction in the case of surface vacancy formation. We have calculated the vacancy formation energies as these can be viewed as a measure of surface activity in the catalytic reaction with various adsorbates. We find that CeO2 termination of the (100) surface and modified O2 termination of the (110) surface (O termination) have the lowest vacancy formation energies.