Surface segregation mechanisms in dielectric thin films

It is often assumed that evaporation causes lead and bismuth depletion at the surface of ferroelectric films. However, this is in contrast with evidence that shows surface enrichment of Pb and Bi. A segregation mechanism that is analogous to the diffusion processes observed during the oxidation of metals is described. The presence of an electrochemical potential is discussed, together with the implications on the electrical properties of ferroelectric films.