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 formatio n of the K-XAS PEFS for the 3d-atoms in the compounds: p-d mixture (PD M) which makes allowed the Is-electron transitions to the absorbing at om 3d-states influenced by the screened hole potential and the Is-elec tron transitions to the unoccupied 3d-states of the neighbouring atoms . The intensities of the PDM induced peaks strongly depend on the disp lacement of the absorbing atom from the center of inversion symmetry a nd on the X-ray polarization vector e direction. Taking into account t his 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 s tudied.