Soft Phonon Mode Dynamics in Aurivillius Type Structures

TL;DR

This study investigates the soft phonon modes in Aurivillius structures, particularly Bi4Ti3O12, revealing their temperature-dependent behavior and the role of Bi-O bonds and cations in structural phase transitions and ferroelectricity.

Contribution

It combines spectroscopy, atomic analysis, and first-principles calculations to identify and analyze soft phonon modes in Aurivillius materials, highlighting their role in phase transitions.

Findings

Discovered three soft phonon modes with strong temperature dependence.

Identified anharmonic Bi-O bonds as key to phonon softening.

Bi cations are crucial for ferroelectricity emergence.

Abstract

We report the dynamics of soft phonon modes and their role towards the various structural transformations in Aurivillius materials by employing terahertz frequency-domain spectroscopy, atomic pair distribution function analysis, and first-principles calculations. We have chosen Bi4Ti3O12 as a model system and identified soft phonon modes associated with the paraelectric tetragonal to the ferroelectric monoclinic transition. Three soft phonon modes have been discovered which exhibit a strong temperature dependence. We have determined that the anharmonicity in Bi-O bonds plays a significant role in phonon softening and that Bi cations play an important role in the emergence of ferroelectricity.