The ferroelectric-paraelectric phase transition in BiFeO3: crystal structure of the orthorhombic beta-phase

TL;DR

This study uses neutron diffraction to analyze the phase transition in BiFeO3, revealing a first-order transition from ferroelectric to paraelectric phases and detailing the crystal structure of the orthorhombic beta phase.

Contribution

It provides detailed structural insights into the orthorhombic beta phase of BiFeO3 and clarifies the nature of its phase transition, which was previously not well understood.

Findings

BiFeO3 transitions from rhombohedral to orthorhombic phase between 820°C and 830°C

The phase transition is first-order with phase coexistence

Metastability prevents observation of the cubic gamma phase above 925°C

Abstract

A detailed investigation using variable temperature powder neutron diffraction demonstrates that BiFeO3 undergoes a phase transition from the ferroelectric alpha phase (rhombohedral, R3c) to a paraelectric beta phase (orthorhombic, Pbnm) between 820 oC and 830 oC. Co-existence of both phases over a finite temperature interval, together with abrupt changes in key structural parameters, confirm that the transition is firstorder. The beta phase corresponds to the GdFeO3-type perovskite. The metastability of BiFeO3 relative to Bi2Fe4O9 above 810 oC precludes observation of a reported cubic gamma phase above 925 oC under the present experimental conditions.