X-ray photoelectron spectroscopy of La0.5Sr0.5MnO3

Cathode electrode for solid oxide fuel cells (SOFC) consisting of strontium-doped lanthanum manganite (La0.5Sr0.5MnO3: LSM) was prepared with a modified sol-gel process. Its surface chemical composition was studied by X-ray photoelectron spectroscopy (XPS). As prepared LSM, the oxidation state of Mn ions is +3.5, which is consistent with oxidation state calculated from the chemical formula. The ratio of La, Sr and Mn ions is about 1/1.1/2. After the sample was heated in ultrahigh vacuum (UHV) chamber with oxygen partial pressure of 10−6 mbar at 600 °C for about 3 h, the oxidation state of Mn ions decreases from +3.5 to +3.3 probably due to the generation of oxygen vacancy on the surface. A little Sr rich phase was formed on the surface duo to the formation of SrO.