Charge-stripe order in the electronic ferroelectric LuFe2O4

TL;DR

This study investigates charge ordering in LuFe2O4, revealing a well-defined charge stripe phase with non-sinusoidal charge density waves that contribute to its ferroelectric properties, and observes temperature-dependent structural domain changes.

Contribution

It provides detailed in-situ TEM analysis of charge order structures and identifies the charge stripe phase as key to ferroelectricity in LuFe2O4, highlighting temperature-driven domain variations.

Findings

Charge order forms a stripe phase at low temperatures.

Charge density waves are non-sinusoidal, creating electric dipoles.

Structural domains vary significantly with temperature.

Abstract

The structural features of the charge ordering states in LuFe2O4 are characterized by in-situ cooling TEM observations from 300K down to 20K. Two distinctive structural modulations, a major q1= (1/3, 1/3, 2) and a weak q2=q1/10 + (0, 0, 3/2), have been well determined at the temperature of 20K. Systematic analysis demonstrates that the charges at low temperatures are well crystallized in a charge stripe phase, in which the charge density wave behaviors in a non-sinusoidal fashion resulting in elemental electric dipoles for ferroelectricity. It is also noted that the charge ordering and ferroelectric domains often change markedly with lowering temperatures and yields a rich variety of structural phenomena.