Issue 21, 2014

Mode coupling between nonpolar and polar phonons as the origin of improper ferroelectricity in hexagonal LuMnO3

Abstract

Currently, the most puzzling problem associated with the hexagonal LuMnO3 (h-LMO) is a large temperature-gap between the structural phase transition to the polar P63cm phase at ∼1290 K and the emergence of the spontaneous polarization at a substantially reduced temperature, ∼750 K. Interestingly, this large temperature-gap is not limited to h-LMO but is a universal phenomenon valid for other rare-earth manganites. We have examined this important issue by exploiting first-principles calculations. It is shown that the structural phase transition to the polar P63cm phase from the nonpolar P63/mmc phase of h-LMO is mediated by the freezing-in of the zone-boundary K3 phonon. However, the ferroelectric polarization remains at a negligibly small value until the amplitude of the K3 phonon reaches a certain critical value above which the coupling of the polar Γ2 mode with the nonpolar K3 mode is practically turned on. This coupling-induced polarization explains the observed temperature-gap in h-LMO as well as other rare-earth manganites.

Graphical abstract: Mode coupling between nonpolar and polar phonons as the origin of improper ferroelectricity in hexagonal LuMnO3

Article information

Article type
Paper
Submitted
27 tammi 2014
Accepted
14 maalis 2014
First published
14 maalis 2014

J. Mater. Chem. C, 2014,2, 4126-4132

Author version available

Mode coupling between nonpolar and polar phonons as the origin of improper ferroelectricity in hexagonal LuMnO3

S. Song, J. Lee and H. M. Jang, J. Mater. Chem. C, 2014, 2, 4126 DOI: 10.1039/C4TC00182F

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