Confinement kinetics in a KTN:Cu crystal: Experiment and theory

A dielectric relaxation process with nonmonotonic temperature dependence was observed in KTN:Cu at the ferroelectric phase. The kinetics of this process were interpreted in terms of the free volume model. It is argued that in this system the small Cu+ ions that are frozen in an off center position in the large K+ sites provide the necessary latitude for the relaxation model. The potential field of the relaxing ions is described in terms of the phenomenological Buckingham potential. The temperature dependence of the relaxation time is derived by assuming that the effective ionic radius of the Cu+ ion changes as it shifts in its site. Similar results are obtained when the Lennard-Jones potential is applied.