High-Temperature Phonon Spectra of Multiferroic BiFeO3 from Inelastic Neutron Spectroscopy

TL;DR

This study investigates how phonon spectra in multiferroic BiFeO3 change across various high temperatures, revealing phase transitions and structural modifications through neutron scattering and ab-initio simulations.

Contribution

It provides detailed high-temperature phonon spectra of BiFeO3 and links observed vibrational features to structural phase transitions and potential oxygen vacancy effects.

Findings

Identified phonon mode changes at T_C and T_N

Detected structural modifications near T_D

Matched experimental data with ab-initio simulations

Abstract

We report inelastic neutron scattering measurements of the phonon spectra in a pure powder sample of the multiferroic material BiFeO3. A high-temperature range was covered to unravel the changes in the phonon dynamics across the Neel (T_N ~ 650 K) and Curie (T_C ~ 1100 K) temperatures. Experimental results are accompanied by ab-initio lattice dynamical simulations of phonon density of states to enable microscopic interpretations of the observed data. The calculations reproduce well the observed vibrational features and provide the partial atomic vibrational components. Our results reveal clearly the signature of three different phase transitions both in the diffraction patterns and phonon spectra. The phonon modes are found to be most affected by the transition at the T_C. The spectroscopic evidence for the existence of a different structural modification just below the decomposition limit (T_D ~ 1240 K) is unambiguous indicating strong structural changes that may be related to oxygen vacancies and concomitant Fe3+ to Fe2+ reduction and spin transition.