Phase separation and ferroelectric ordering in charge frustrated LuFe2O4-x

TL;DR

This study investigates charge ordering and phase separation in LuFe2O4-x, revealing two distinct charge modulations and their ferroelectric properties, influenced by oxygen content, through microscopy, structural analysis, and theoretical simulations.

Contribution

It uncovers the coexistence of two charge-ordered phases with different modulations and demonstrates their ferroelectric ordering, highlighting the role of oxygen stoichiometry.

Findings

Presence of two charge order ground states with distinct modulations.

Incommensurate Q2 state is stable in oxygen-deficient samples.

Both phases exhibit ferroelectric ordering as shown by simulations.

Abstract

The transmission electron microscopy observations of the charge ordering (CO) which governs the electronic polarization in LuFe2O4-x clearly show the presence of a remarkable phase separation at low temperatures. Two CO ground states are found to adopt the charge modulations of Q1 = (1/3, 1/3, 0) and Q2 = (1/3 + y, 1/3 + y, 3/2), respectively. Our structural study demonstrates that the incommensurately Q2-modulated state is chiefly stable in samples with relatively lower oxygen contents. Data from theoretical simulations of the diffraction suggest that both Q1- and Q2-modulated phases have ferroelectric ordering. The effects of oxygen concentration on the phase separation and electric polarization in this layered system are discussed.