Symmetry changes at the ferroelectric transition in the multiferroic YMnO3

TL;DR

This study reveals the symmetry change at the ferroelectric transition in YMnO3, confirming it as a proper ferroelectric and elucidating the origin of its ferroelectricity through synchrotron diffraction and group analysis.

Contribution

First identification of the symmetry change at the ferroelectric transition in YMnO3, clarifying its proper ferroelectric nature and the structural origin of ferroelectricity.

Findings

YMnO3 undergoes a symmetry change at TFE near 1023K.

The intermediate phase has P63/mcm symmetry.

Ferroelectricity arises from tilting of MnO5 polyhedra.

Abstract

We have identified, for the first time, the change in symmetry at the ferroelectric transition TFE near 1023K of the ferroelectromagnet YMnO3. This transition takes place 300K below the transition to the centrosymmetric state at TIP. Single crystal synchrotron diffraction coupled to a group theoretical analysis show that the paraelectric intermediate phase between TIP and TFE has P63/mcm symmetry. This proves that YMnO3 is a proper ferroelectric and not an improper ferroelectric, as suggested by a previous group theoretical assignment. The origin of the ferroelectricity is caused by a correlated tilting of the MnO5 polyhedra along the (100), (110) and (010) directions