Infrared phonon dynamics of multiferroic BiFeO3 single crystal

TL;DR

This study presents the first infrared reflectivity measurements on a BiFeO3 single crystal, identifying phonon modes and revealing that the ferroelectric transition is driven by soft-mode phonon behavior.

Contribution

It provides unambiguous identification of phonon modes in BiFeO3 single crystals, clarifying previous discrepancies between theory and ceramic data.

Findings

Identified all predicted phonon modes in BiFeO3 single crystal.

Demonstrated softening of the lowest frequency E mode with temperature.

Confirmed the soft-mode driven ferroelectric transition in BiFeO3.

Abstract

We discuss the first infrared reflectivity measurement on a BiFeO3 single crystal between 5 K and room temperature. The 9 predicted ab-plane E phonon modes are fully and unambiguously determined. The frequencies of the 4 A1 c-axis phonons are found. These results settle issues between theory and data on ceramics. Our findings show that the softening of the lowest frequency E mode is responsible for the temperature dependence of the dielectric constant, indicating that the ferroelectric transition in BiFeO3 is soft-mode driven.