FORMATION OF THE PRE-EDGE STRUCTURE AND DRAMATIC POLARIZATION DEPENDENCE OF TI K-NEXAFS IN PBTIO3 CRYSTALS

Ti K NEXAFS in a PbTiO3 crystal is calculated within full multiple scattering method. The pre-edge peak in the spectra is shown to be mainly formed due to the p-d mixture at the Ti site caused by the breakdown of the central symmetry of the Ti atom local environment. The contribution of the electron transitions from the Ti K-level into unoccupied states of the neighbouring atoms is comparatively small. The contribution of the quadrupole transitions is negligible. The pre-edge peak and one of the peaks above the main Ti K-edge are shown to depend dramatically on the X-ray polarization direction in the tetragonal phase. These features could be employed for studies of small atomic displacements in the perovskite-structure crystals.