The Nature of High Dielectric Constant in Relaxor Ferroelectric

Abstract

Ferroelectrics with disordered structure are complex oxide systems that exhibit diffuse phase transition properties. Some of them are usual ferroelectric solid solutions with the nonuniform allocation of ions but the others belong to “superparaelectrics” = relaxor ferroelectrics. To draw a line between them, a macroscopic experimental test-method is proposed. It is based on broadband dielectric spectroscopy conducted in wide temperature interval: ϵ*(ν, T) = ϵ′ − iϵ″. In this connection, the difference between actual dielectric constant ϵ = ϵ′ and apparent (effective) dielectric constant ϵ _eff is specialized. Ordinary ferroelectric is defined by very sharp ϵ′(T)-maximum at the Curie temperature T _C but frequency shift of this maximum is absent. Against, any type of disordered ferroelectric exhibit strongly diffused ϵ′-maximum, moreover, the temperature of the ϵ′ maximum increases as frequency grows. It is shown that smooth growing of T _max(log ν) is typical for usual ferroelectric solid solution with diffuse phase transition while a key feature of relaxor ferroelectric is broken or bifurcated T _max(log ν)-line.

Keywords:

• Relaxor ferroelectric
• diffuse phase transition
• dielectric spectroscopy