Quantitative Mapping of Chemical Defects at Charged Grain Boundaries in a Ferroelectric Oxide

Abstract

Polar discontinuities, as well as compositional and structural changes at oxide interfaces can give rise to a large variety of electronic and ionic phenomena. In contrast to earlier work focused on domain walls and epitaxial systems, this work investigates the relation between polar discontinuities and the local chemistry at grain boundaries in polycrystalline ferroelectric ErMnO3. Using orientation mapping and scanning probe microscopy (SPM) techniques, the polycrystalline material is demonstrated to develop charged grain boundaries with enhanced electronic conductance. By performing atom probe tomography (APT) measurements, an enrichment of erbium and a depletion of oxygen at all grain boundaries are found. The observed compositional changes translate into a charge that exceeds possible polarization‐driven effects, demonstrating that structural phenomena rather than electrostatics determine the local chemical composition and related changes in the electronic transport behavior. The study shows that the charged grain boundaries behave distinctly different from charged domain walls, giving additional opportunities for property engineering at polar oxide interfaces.

Pressure Control of Nonferroelastic Ferroelectric Domains in ErMnO3

“…The domain structure displayed in Figure a (σ = 0 MPa) is consistent with previous observations, exhibiting a rather isotropic network of vortex domains within the different grains. The domain walls typically terminate at the grain boundaries and do not extend into adjacent grains, indicating that the ferroelectric domains in neighboring grains are largely independent as discussed in refs and . Increasing the mechanical pressure during cooling to σ = 24 MPa transforms the isotropic vortex-like domain structure into a more stripe-like pattern (Figure b) in all grains, independent of their crystallographic orientation relative to the direction of the applied pressure.…”

Magnetoelectric coupling at the domain level in polycrystalline hexagonal ErMnO3

“…The spatial resolution of Rcos# (amplitude R and phase # of the piezoelectric response) allows to distinguish domains with an antiparallel orientation of the ferroelectric polarization, while the grain boundaries separating grains of different crystallographic orientations are displayed by dashed white lines as explained in detail elsewhere. [22][23][24][25] The PFM image reveals a pronounced contrast, corresponding to the characteristic ferroelectric domain structure of polycrystalline h-ErMnO 3 , featuring a mixture of vortex-and stripe-like domains that form at T c % 1420 K. 26,27 To explore the low-temperature response of our polycrystalline h-ErMnO 3 sample, we measure the macroscopic dielectric permittivity as a function of temperature over 2-250 K for a range of frequencies from 1 to 10 3 Hz. As displayed in Fig.…”