The nature of high dielectric constant in relaxor ferroelectric

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: epsilon*(nu, T ) = epsilon' - i epsilon'. In this connection, the difference between actual dielectric constant epsilon = epsilon' and apparent (effective) dielectric constant epsilon eff is specialized. Ordinary ferroelectric is defined by very sharp epsilon'( 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 epsilon'-maximum, moreover, the temperature of the epsilon' maximum increases as frequency grows. It is shown that smooth growing of T-max (log nu) 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 nu)-line.