Passivation of the La2NiMnO6 double perovskite to hydroxylation by excess nickel, and the fate of the hydroxylated surface upon heating

Abstract The double perovskites with a total elemental content of LaNi 0.5 Mn 0.5 O 3 and LaNi 0.75 Mn 0.25 O 3 were synthesized by solid state methods, although the LaNi 0.75 Mn 0.25 O 3 material underwent phase separation into NiO, LaNiO 3 and LaNi 0.5 Mn 0.5 O 3 . Auger Electron Spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) indicated substantial lanthanum surface segregation for the LaNi 0.5 Mn 0.5 O 3 material, which formed an altered La(OH) 3 layer 50–100 monolayers in thickness. The La(OH) 3 could be removed by Ar + sputtering to achieve a surface of approximately stoichiometric concentration. Heating the La(OH) 3 -covered LaNi 0.5 Mn 0.5 O 3 did not regenerate the double perovskite but rather produced an overlayer of La 2 O 3 . While the LaNi 0.75 Mn 0.25 O 3 material displayed extensive phase separation, the excess nickel appeared to prevent substantial lanthanum surface segregation.