Ferroelectric Phase Transitions Viewed Via Nonlinear Dielectric Response

Abstract

Experimental data on the nonlinear dynamic responses of barium titanate (discontinuous ferroelectric phase transition, PT), triglycine sulphate (continuous PT), as well as the prototype relaxor lead magnoniobate, and the weakly doped quantum paraelectric K_0.995Li_0.005TaO₃ are presented. The classic ferroelectrics display all features of the third order dielectric susceptibility, χ ₃ , as predicted by mean-field theory (including the change of sign of χ ₃ at the continuous PT). On the other hand, the positive sign of χ ₃ measured on the relaxor PMN is due to the presence of polar nanoregions and their specific contribution to the dielectric response measured at enhanced electric field.

Keywords:

• Nonlinear dielectric response
• phase transitions
• ferroelectrics
• relaxors
• dipolar glasses

Acknowledgment

Thanks are due to the Polish Ministry of Science for financial support under grant No. N N507 455034. WK thanks the Foundation for Polish Science for an Alexander-von-Humboldt Honorary Fellowship. Stimulating discussions with R. Pirc are gratefully acknowledged.