Effect of surface treatments on Li0.30Ln0.57TiO3 (Ln = La, Nd) perovskite ceramics: an X-ray photoelectron spectroscopy study

To explain the sensitivity of some titanate ceramics to pH variation in aqueous solutions, the lithium lanthanum titanate (LLTO) and lithium neodymium titanate (NLTO) surfaces were analysed by X-ray photoelectron spectroscopy. The surface of LLTO was modified by chemical treatments and sputtering. XPS spectrum of LLTO exhibits the peaks of lanthanum (La 3d3/2, La 3d5/2, La 4p, La 4d), titanium (Ti 2p1/2, Ti 2p3/2) and oxygen (O 1s). However, the immersion of the ceramic in sodium hydroxide or surface sputtering affect mainly the narrow-scan spectra of oxygen (O 1s). This study reveals that an acido-basic reaction takes place in the neighbourhood of the TiO6 octahedra of the perovskite. The results also suggest that hydroxyl species may associate with lanthanum. Furthermore, the study on C 1s line rules out the assumption that CO 3 2 - species are involved in the pH detection.