| Multiple-scattering curved-wave cluster calculations using the FEFF6 code obtained from the University of Washington are used to provide new understanding of X-ray Absorption Fine Structure (XAFS). Both near-edge (NEXAFS) and extended (EXAFS) XAFS are interpreted. It was found that the FEFF6 code may be utilized to interpret UV spectra for the alkali halides. A new iterative approach for separating the experimental L{dollar}sb2{dollar} and L{dollar}sb3{dollar} contributions is given and some peaks in the alkali halide spectra are reassigned.; A novel differential XAFS technique is developed that utilized the difference in two very similar XAFS spectra. It is shown that such difference spectra, {dollar}Deltachi{dollar}, have amplitudes proportional to the difference in path length and Debye-Waller factor. Contributions from paths that have not changed between the two samples thus cancel out, allowing for multiple scattering paths of small intensity to be isolated for analysis. The technique allows an isolation of the double scattering Zn-O-O-Zn path, which traverses the near tetrahedral O-Zn-O angle in the zincate ion, and thus reveals the distortion of the ion due to M-cation zincate-anion pair formation. The strength of this interaction is found to decrease with cation size ({dollar}rm Lisp+>Nasp+>Ksp+>Rbsp+{dollar}) and thereby reveals the role of Li{dollar}sp+{dollar} in preventing the polymerization of zincate ion in the Zn electrode. Application is also made to the Ni electrode, where NEXAFS data for the {dollar}beta{dollar}-Ni(OH){dollar}sb2, beta{dollar}-NiOOH, and BaNiO{dollar}sb3{dollar} reference materials and the charged Ni oxide electrode are analyzed. These results reveal that the nominal oxidation state in the charged Ni electrode is around 3.5, which is consistent with previous observations.; Finally, systematic changes in the "atomic" XAFS (AXAFS) structure, with composition of some Pt/Ru alloys and applied potential of a charged Pt electrode, are reported for the first time and shown to result from changes in the inter-atomic potential. FEFF6 calculations reproduce the systematic change but overestimate the magnitudes. A long-range effect is found to exist in the AXAFS for the zincate ion and attributed to changes in the zero of energy. AXAFS has the potential to provide a new tool for examining electronic structure in situ in a wide variety of materials. |
