X-Ray Absorption Fine Structure Applied to Ferroelectrics

Abstract

This chapter is devoted to explaining the foundation and merits of the application of synchrotron radiation for studying the X-ray absorption fine structure (XAFS) in ferroelectric materials. XAFS in the local order allows the follows: determining the oxidation states, interatomic distances, Debye-Waller factors and the coordination number of atoms at the first few shells around the absorbing atom, up to 0.5 nm. The text explains the features of the photoelectric effect, as well as its relationship with the absorption edges of each element. Applying the Fermi’s Golden Rule, it is explained that the fine structure of absorption edge spectra is the result of the interference of the photoelectron single- and multiple-scattering. This gives rise to the effects of X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS). The content includes significant effects for the study of ferroelectric materials in XANES: energy shift of the edge position, pre-edge transitions and white-lines. Subsequently, the experimental methods and EXAFS spectra processing, by both empirical methods and theoretical models with multiple scattering paths, are presented. Finally, we offer some works representing XAFS applied to ferroelectrics, from the explanation of the displacive or order-disorder nature of the materials PbTiO3 and BaTiO3, to those dedicated to relaxors and Aurivillius oxides.