Surface phase diagrams of La-based perovskites towards the O-rich limit from first principles
Journal article, Peer reviewed
MetadataShow full item record
Original versionPhysical Chemistry, Chemical Physics - PCCP. 2019, 21 (24), 12859-12871. 10.1039/c9cp02288k
The exposed termination of transition-metal oxide surfaces plays a major role in determining the catalyst performance in redox reactions. In this contribution, the surface phase diagrams of LaMO3(001) (M = Sc–Fe) and LaMO3(110) (M = Co–Cu) are constructed by using the DFT+U method. The stabilities of six terminations derived from the stoichiometric MO2 and LaO surfaces are determined over a wide range of temperatures and oxygen partial pressures. The surface phase diagrams are calculated towards the O-rich limit in which the chemical potential of oxygen anions of perovskites equals that of gas-phase oxygen while the chemical potential of M cations is limited by thermodynamic boundary conditions. It is found that the surface phase diagrams are closely related to the reducibility of M cations, which is reflected in the oxygen adsorption energy and oxygen vacancy formation energy on the MO2- and LaO-terminated surfaces and can be measured by the third ionization energies of the M2+ cations. According to the surface phase diagrams, the most stable surface termination is predicted to be of MO2 type for LaMO3 (M = Sc–Fe) and LaO type for LaMO3 (M = Co–Cu) under solid oxide fuel cell operating conditions. Because the M cations become more readily reduced on going from left to right across the period, LaCoO3 may form an oxygen-deficient crystal structure at high temperatures and LaNiO3 and LaCuO3 would be decomposed into oxides containing the transition metals in a lower oxidation state.