INTERACTION OF PBZRXTI1-XO3 (PZT) WITH NI - ROLE OF SURFACE-DEFECTS

The surface properties of lead zirconate titanate (PZT) and its intera ction with a metallic overlayer have been investigated. X-ray photoele ctron spectroscopy (XPS) was used to study the composition and chemica l states of the substrate and adsorbate ions. Results in PZT were comp ared to those in iso-structural SrTiO3. It was found that, on polished PZT and SrTiO3 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 sample s even though there is no evidence of oxygen depletion at the surface. The relationship between this behaviour and sputtering-related defect s has been studied by quantifying bombardment related changes to obtai n defect profiles. In PZT, there is depletion of Pb2+ accompanied by c hemical reduction to metallic Pb over a depth of 30 or more monolayers . This species is found to be insensitive to surface adsorbates. In bo th PZT and SrTiO3, Ti4+ ions in the outer two to three monolayers are reduced to Ti3+. This defect reacts easily with adatoms (metals, atmos pheric contaminants, etc) to change back to its original Ti4+ state. S ince this defective species acts as a source of electrons, and is comm on 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.