Indieect quadeupole-quadrupole interaction via soft phonon modes as a mechanism of NQR line critical, broadening in ferroelectrics

Abstract

A theoretical consideration of indirect quadrupole-quadrupole interaction (IQQI) through soft phonon modes in the crystals with phase transitions is presented. The IQQI due to the quadratic interaction with a ferroelectric soft transverse optical phonon mode, IQQI due to the linear Interaction with the soft transverse optical phonon electric field, gradient and IQQI due to the linear interaction with a soft mode condensed on the Brillouin zone boundary are considered. It is shown that the IQQI through soft phonon modes is responsible for an efficient mechanism of NQR and NMR of quadrupole nuclei lines critical shift and broadening.