Terahertz and Infrared Studies of Antiferroelectric Phase Transition in Multiferroic Bi_0.85Nd_0.15FeO_3

TL;DR

This study investigates the antiferroelectric phase transition in Bi_0.85Nd_0.15FeO_3 ceramics using high-frequency dielectric measurements, revealing phonon hardening, a THz dielectric relaxation, and their effects on dielectric permittivity near 600 K.

Contribution

It provides new insights into the THz dielectric relaxation and phonon behavior associated with the antiferroelectric transition in this multiferroic material, highlighting its phase boundary characteristics.

Findings

Phonons harden below 600 K during the transition.

A strong THz dielectric relaxation appears in the paraelectric phase.

Relaxation frequency softens and disappears below 450 K.

Abstract

High-frequency dielectric studies of Bi_0.85Nd_0.15FeO_3 ceramics performed betweeen 100 and 900 K reveal hardening of most polar phonons on cooling below antiferroelectric phase transition, which occurs near 600 K. Moreover, a strong THz dielectric relaxation is seen in paraelectric phase. Its relaxation frequency softens on cooling towards Tc ~ 600 K, its dielectric strength simultaneously decreases and finaly the relaxation disappears from the spectra below 450 K. Both phonon and dielectric relaxation behavior is responsible for a decrease in the dielectric permittivity at the antiferroelectric phase transition. Origin of unusual strong THz dielectric relaxation in paraelectric phase is discussed. Bi_0.85Nd_0.15FeO_3 structrure lies on the phase boundary between polar rhombohedral and non-polar orthorhombic phase and owing to this the polarization rotation and polarization extension can enhance the piezoelectric response of this system. Similarities and discrepancies with lead-based piezoelectric perovskites, exhibiting morphotrophic phase boundary between two ferroelectric phases, are discussed.