PRE-EDGE FINE-STRUCTURE OF THE 3D ATOM K X-RAY-ABSORPTION SPECTRA ANDQUANTITATIVE ATOMIC-STRUCTURE DETERMINATIONS FOR FERROELECTRIC PEROVSKITE STRUCTURE CRYSTALS

A complete interpretation is proposed for the pre-edge fine structure (PEFS) of the x-ray Ti K-absorption spectra for ATiO(3) perovskite str ucture crystals. The interpretation is based on the results of numerou s calculations performed by a modified full multiple scattering method which provides the theoretical spectra for the 3d transition metal ox ides in fair agreement with experiment. It is shown that the three mai n peaks in the PEFS have quite different origin. The first long-wave s ide peak A is caused mainly by quadrupole transitions. The middle peak B is caused by the p-d mixture effect and the high intensity of it is considered to be a qualitative spectroscopic indication of ferroelect ricity in the perovskite structure crystal. A simple formula is obtain ed which expresses the area under peak B through the lattice constants and mean-square displacement of the absorbing Ti atom from the instan taneous centre of the coordination polyhedron. The peak B area average d over thermal atomic vibrations is determined by the three-particle a tomic distribution function. The short-wave side peak C is caused by t he Tr Is electron transition to the unoccupied 3d states of the neighb ouring transition metal atoms. We show that an additional peak C' on t he short-wave side of peak C occurs if there are 4d atoms (for instanc e Zr atoms in the vicinity of the absorbing Ti atom in the PbTixZr1-xO 3 (PZT) solid solution) within the oxygen atom octahedrons surrounding the absorbing 3d atom. The area under peak C' is directly determined by the average number of 4d atoms in the vicinity of the absorbing Ti one.