Pre-edge fine structure (PEFS) of the K-XAS for the 3d atoms in compounds: A new tool for quantitative atomic structure determination

The two mechanisms are shown to be mainly responsible for the formation of the K-XAS PEFS for the 3d-atoms in the compounds: p-d mixture (PDM) which makes allowed the 1s-electron transitions to the absorbing atom 3d-states influenced by the screened hole potential and the 1s-electron transitions to the unoccupied 3d-states of the neighbouring atoms. The intensities of the PDM induced peaks strongly depend on the displacement of the absorbing atom from the center of inversion symmetry and on the X-ray polarization vector e direction. Taking into account this dependence and employing the experimental Ti K-XAS for the PbTiO₃ monocrystal measured for different temperatures and directions of the vector e the ferroelectric phase transition in this crystal has been studied.