High resolution x-ray absorption spectroscopy (XAS) affords new insight into the microscopic properties of perovskite transition metal oxides. Interpretation of XAS spectra in transition metal oxides requires theoretical tools capable of describing relativistic and many-body effects. In this work, full relativistic (SPR-KKR) and multiplet calculations (CTM4XAS) are carried out and compared to experimental multiedge XAS spectra of BaTiO${}_{3}$ single crystals. The impact of relativistic and many-body effects on the calculated density of states and x-ray absorption near edge structure spectra are individually considered.
EXAFS (extended X‐ray absorption fine structure) investigations are reported concerning the thermal expansion behaviour of silver in an extended range of temperature from 10 K to about 950 K measured in transmission mode. Both the ratio method and an EXAFS fitting procedure were applied to reveal the temperature dependence of EXAFS parameters. Models based on quantum and classical thermodynamic perturbation theory have been used to interpret experimental data and compared to XRD (X‐ray diffraction) results of bulk silver material. The description of thermodynamic data of thermal expansion of silver in the complete range of temperature by EXAFS Spectroscopy was successful by first calculations using third order quantum perturbation theory.
The magnetism-induced symmetry breaking in photoelectron diffraction patterns of $2{p}_{3∕2}$ photoelectrons from a ferromagnetic Fe(001) single crystal surface is studied experimentally and theoretically. Two-dimensional photoelectron intensity angular distribution patterns were recorded at 1193 eV photon energy for both helicities of the circularly polarized light and for opposite magnetization directions of the sample by a display-type spherical mirror analyzer, which allows simultaneous energy and momentum analysis of emitted photoelectrons. The macroscopic magnetization of the sample induces an additional symmetry breaking in the circular dichroism of the $\mathrm{Fe}\phantom{\rule{0.3em}{0ex}}2{p}_{3∕2}$ photoelectron angular distribution patterns which is related to the presence of magnetic moments on the Fe atoms. Multiple-scattering cluster photoelectron diffraction calculations agree well with experiment, and reproduce even fine details of the observed photoelectron diffraction features. The details of that breaking of mirror symmetry of photoelectron scattering in the plane spanned by light incidence and electron emission due to the presence of a magnetization within that plane depends both on the structure and the magnetism of the sample. In connection with multiple scattering calculations, measurements of the magnetism-induced symmetry breaking by two-dimensional photoelectron diffraction patterns may thus be used as a powerful tool for simultaneous structural and magnetic investigations of single crystalline magnetic samples and ultrathin films.
Extended x-ray absorption fine structure investigations are reported concerning the thermal expansion behavior of silver in a wide range of temperatures from 10 to about 950 K as measured in the transmission mode. Models based on the quantum and classical thermodynamic perturbation theory are used to interpret the experimental data and compared to x-ray diffraction results of the crystalline silver material. To this aim, the third- and fourth-order perturbation formulas of the cumulants and of the thermal expansion coefficient have been developed by means of the quantum-statistical theory and are presented here. By using these formulas, the thermal expansion of silver bonds can be described by the temperature-dependent first cumulants as well as by an anharmonic potential function in correlation with the cumulant expansion in the complete range of temperatures.
An analysis of the extended X‐ray absorption fine structure is developed, in which experimental modulations are projected onto calculated ones from backscattering at single neighboring atoms. From the extended X‐ray absorption fine structures of single crystals of SrTiO 3 and BaTiO 3 , initial values for nearest neighbor distances are obtained. In addition, a preference for the element of the next nearest neighbor can be given.
