DEFECT CHEMISTRY OF LA2NI1-XMXO4 (M = MN, FE, CO, CU) : RELEVANCE TO CATALYTIC BEHAVIOR

Atomistic computer simulation techniques are used to investigate the defect properties of the La2Ni1-xMxO4 (M = Mn, Fe, Co, Cu) layered perovskite which are related to the mode of operation of the catalyst. The theoretical techniques are based upon efficient energy minimization procedures and Mott−Littleton methodology for accurate defect modeling. Effective ionic pairwise interatomic potentials correctly reproduce the tetragonal crystal structure. The formation energy of intrinsic atomic defects of the Schottky and Frenkel type are not particularly favorable. The oxidation of La2NiO4+δ was found to be an exothermic process with charge compensation occurring via hole formation preferentially on the Ni site. The highest solubility, for a range of dopants, is calculated for Sr and Ca, in accord with observation. Hole formation was most favorable for Mn > Fe > Co > Ni(undoped) > Cu, demonstrating that Mn and Fe enhance Ni(III) hole formation, which is believed to be an important factor in the observed cataly...