Interaction of PbZrxTi(1-x)O3 (PZT) with Ni: Role of Surface Defects

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The surface properties of lead zirconate titanate (PZT) and its interaction with a metallic overlayer have been investigated. X-ray photoelectron spectroscopy (XPS) was used to study the composition and chemical states of the substrate and adsorbate ions. Results in PZT were compared to those in iso-structural SrTiO3. It was found that, on polished PZT and SiTiO3 surfaces at room temperature, a fraction of the first monolayer of evaporated Ni is oxidized to form Ni-O type bonds. On the other hand, if the surface is ion bombarded prior to deposition, the extent of this chemical interaction is strongly reduced in both samples even though there is no evidence of oxygen depletion at the surface. The relationship between this behaviour and sputtering-related defects has been studied by quantifying bombardment related changes to obtain defect profiles. In PZT, there is depletion of Pb2+ accompanied by chemical reduction to metallic Pb over a depth of 30 or more monolayers. This species is found to be insensitive to surface adsorbates. In both PZT and SrTiO3, Ti4+ ions in the outer two to three monolayers are reduced to Ti3+. This defect reacts easily with adatoms (metals, atmospheric contaminants, etc) to change back to its original Ti4+ state. Since this defective species acts as a source of electrons, and is common to both solids which show similar adsorption behaviour, it must be responsible for reduced oxidation of Ni on the sputtered surface. The scientific significance of these observations and their implication to practical properties have been discussed.