Structural and surface characterization of perovskite-type oxides; influence of A and B substitutions upon oxygen binding energy

Monophasic samples of seven different oxides with perovskite structure, and also gamma-NaAlO2 have been prepared for catalytic applications. They have been characterized by X-ray diffraction and electron microscopy, then by X -ray photoelectron spectroscopy (XPS). The XPS spectra of LaAlO3, La0.9Sr0. 8Al0.8Cu0.1Ru0.1O3, La0.8Sr0.2Al0.8Cu0.1Ru0.1O3 and gamma-NaAlO2 contained only one well-defined O 1s peak. The binding energy obtained from the oxyge n peak of the perovskites (529.8 eV) was, however, significantly different from that of gamma-NaAlO2 (532.2 eV). The other perovskite oxides, La0.9Ca0 .1AlO3, La0.8Ca0.2AlO3, La0.8Sr0.2AlO3 and LaAl0.8Cu0.2O3 had two more or l ess well-resolved O 1s peaks separated by 2.4 eV. Tentatively, we have inte rpreted these observations to mean that, in the latter compounds, the surfa ce is reconstructed so that the Al3+ ions have changed their coordination f rom octahedral to tetrahedral. (C) 1998 Kluwer Academic Publishers.