SURFACE-PROPERTIES OF PEROVSKITES AND THEIR RESPONSE TO ION-BOMBARDMENT

X-ray photoelectron spectroscopy has been used to study the surface co mposition and chemistry of two perovskites: SrTiO3 and Pb(Zr,Ti)O3 (Co mmonly known as PZT). It is seen that ion bombardment, which is a comm on surface modification technique, can cause substantial changes in th ese oxides. The PZT surface undergoes surface depletion of lead along with chemical reduction of the Pb2+ ion to its metallic state. The Zr/ (Ti+Zr) ratio also changes with sputtering, but the total oxygen to ca tion ratio is unchanged. On the other hand, the surface stoichiometry of SrTiO3 is almost unaffected by ion bombardment. In all the perovski tes, irrespective of whether the composition changes or not, a substan tial amount of surface Ti is reduced to a lower valency state on sputt ering. Most of this component is restored back to the original Ti4+ st ate when Ni is evaporated on these surfaces, indicating that the reduc ed state is associated with a damaged outermost surface that can be re paired with an adsorbate. The implication of these results to the bond ing properties of these materials have been discussed.