Dielectric discontinuities and multipolar interactions in ferroelectric perovskites

Abstract

Ferroelectric perovskites, in particular KNbO₃, PbTiO₃ and BaTiO₃, are characterized by discontinuities in the dielectric constant at the tetragonal-cubic transition (T∗) as well as by the abrupt disappearance of the spontaneous polarization which goes from a minimum finite value P_s∗ =P_s (T) to zero at T=T∗. It is shown that, taking into account quadrupolar and higher order terms into the effective field acting on the elementary dipoles lattice, good fits to the observed P_s(T) in a wide temperature range below T∗ and to the inverse dielectric constant discontinuity (C/T_c)[∊₊ ⁻¹(T∗)-∊₋ ⁻¹(T∗)] at T⋍T∗ are obtained for these three perovskites.