3 research outputs found
Self-Poling of BiFeO<sub>3</sub> Thick Films
Bismuth
ferrite (BiFeO<sub>3</sub>) is difficult to pole because of the combination
of its high coercive field and high electrical conductivity. This
problem is particularly pronounced in thick films. The poling, however,
must be performed to achieve a large macroscopic piezoelectric response.
This study presents evidence of a prominent and reproducible self-poling
effect in few-tens-of-micrometer-thick BiFeO<sub>3</sub> films. Direct
and converse piezoelectric measurements confirmed that the as-sintered
BiFeO<sub>3</sub> thick films yield <i>d</i><sub>33</sub> values of up to ∼20 pC/N. It was observed that a significant
self-poling effect only appears in cases when the films are heated
and cooled through the ferroelectric-paraelectric phase transition
(Curie temperature <i>T</i><sub>C</sub> ∼ 820 °C).
These self-poled films exhibit a microstructure with randomly oriented
columnar grains. The presence of a compressive strain gradient across
the film thickness cooled from above the <i>T</i><sub>C</sub> was experimentally confirmed and is suggested to be responsible
for the self-poling effect. Finally, the macroscopic <i>d</i><sub>33</sub> response of the self-poled BiFeO<sub>3</sub> film was
characterized as a function of the driving-field frequency and amplitude
Atomic-Level Response of the Domain Walls in Bismuth Ferrite in a Subcoercive-Field Regime
The atomic-level response of zigzag ferroelectric domain
walls
(DWs) was investigated with in situ bias scanning transmission electron
microscopy (STEM) in a subcoercive-field regime. Atomic-level movement
of a single DW was observed. Unexpectedly, the change in the position
of the DW, determined from the atomic displacement, did not follow
the position of the strain field when the electric field was applied.
This can be explained as low mobility defect segregation at the initial
DW position, such as ordered clusters of oxygen vacancies. Further,
the triangular apex of the zigzag wall is pinned, but it changes its
shape and becomes asymmetric under electrical stimuli. This phenomenon
is accompanied by strain and bound charge redistribution. We report
on unique atomic-scale phenomena at the DW level and show that in
situ STEM studies with atomic resolution are very relevant as they
complement, and sometimes challenge, the knowledge gained from lower
resolution studies
Pressure Control of Nonferroelastic Ferroelectric Domains in ErMnO<sub>3</sub>
Mechanical pressure controls the structural, electric,
and magnetic
order in solid-state systems, allowing tailoring of their physical
properties. A well-established example is ferroelastic ferroelectrics,
where the coupling between pressure and the primary symmetry-breaking
order parameter enables hysteretic switching of the strain state and
ferroelectric domain engineering. Here, we study the pressure-driven
response in a nonferroelastic ferroelectric, ErMnO3, where
the classical stress–strain coupling is absent and the domain
formation is governed by creation–annihilation processes of
topological defects. By annealing ErMnO3 polycrystals under
variable pressures in the MPa regime, we transform nonferroelastic
vortex-like domains into stripe-like domains. The width of the stripe-like
domains is determined by the applied pressure as we confirm by three-dimensional
phase field simulations, showing that pressure leads to oriented layer-like
periodic domains. Our work demonstrates the possibility to utilize
mechanical pressure for domain engineering in nonferroelastic ferroelectrics,
providing a lever to control their dielectric and piezoelectric responses