The beta to gamma (insulator-metal) transition in BiFeO3

TL;DR

This study investigates the high-temperature phase transition in BiFeO3, revealing that the insulator-metal transition occurs without a change in crystal symmetry and identifying the temperature limits of phase stability.

Contribution

The paper provides new neutron diffraction data showing orthorhombic symmetry persists through the insulator-metal transition in BiFeO3, challenging previous symmetry change assumptions.

Findings

Insulator-metal transition occurs with volume contraction.

Orthorhombic symmetry persists across the transition.

Gamma phase remains stable up to ~950°C before decomposition.

Abstract

High temperature powder neutron diffraction experiments have been conducted around the reported beta-gamma, insulator-metal phase transition (~ 930 C) in BiFeO3. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator-metal transition, both the beta and gamma phase of BiFeO3 exhibit orthorhombic symmetry i.e. no further increase of symmetry occurs under the present experimental conditions, contrary to previous suggestions. Furthermore we observe the gamma orthorhombic phase to persist up to a temperature of approximately 950 C before complete decomposition into Bi2Fe4O9 (and liquid Bi2O3), which subsequently begins to decompose at approximately 960 C.