Atomic-scale mechanisms of ferroelastic domain-wall-mediated ferroelectric switching

Abstract

Polarization switching in ferroelectric thin films occurs via nucleation and growth of 180°d omains through a highly inhomogeneous process in which the kinetics are largely controlled by defects, interfaces and pre-existing domain walls. Here we present the first real-time, atomic-scale observations and phase-field simulations of domain switching dominated by pre-existing, but immobile, ferroelastic domains in Pb(Zr 0.2 Ti 0.8 )O 3 thin films. Our observations reveal a novel hindering effect, which occurs via the formation of a transient layer with a thickness of several unit cells at an otherwise charged interface between a ferroelastic domain and a switched domain. This transient layer possesses a low-magnitude polarization, with a dipole glass structure, resembling the dead layer. The present study provides an atomic level explanation of the hindering of ferroelectric domain motion by ferroelastic domains. Hindering can be overcome either by applying a higher bias or by removing the as-grown ferroelastic domains in fabricated nanostructures.

Domain pinning near a single-grain boundary in tetragonal and rhombohedral lead zirconate titanate films

“…16 Significant charge concentrations can exist at 90º domain walls, which then exert a local pressure on 180º domain walls even at sub-switching electric fields due to variations in the local electric field. 17,18 Experimentally, PFM measurements demonstrated that 1-and 2-dimensional defects produce significant pinning of 180º domain walls in ferroelectric films. [19][20][21][22][23][24] The local electric field created by defects and domain wall -domain wall pinning are the major contributions to domain wall pinning.…”

“…[19][20][21][22][23][24] The local electric field created by defects and domain wall -domain wall pinning are the major contributions to domain wall pinning. 17,25 It is widely reported that in tetragonal ferroelectrics the domain structures of adjacent grains are correlated due to local strain and electric fields. 2,26 Ivry et al…”

Theoretical study of ferroelectric nanoparticles using phase reconstructed electron microscopy

“…However, these studies are qualitative and do not provide * cd@anl.gov direct quantitative information about, or images of, the polarization state of the ferroelectric. Recently, high resolution aberration-corrected TEMs have been employed to infer the ferroelectric polarization in PZT thin films by measuring atomic displacements and deviations from centrosymmetry at the unit cell level [9], or strain measurement using geometric phase analysis (GPA) [10] rather than by capturing the electric field that arises from polarization charges.…”

Superdomain dynamics in ferroelectric-ferroelastic films: Switching, jamming, and relaxation

“…Switching of superdomains: Fig.10 shows the TEM photos of a ferroelastic superdomain switching large amounts of charge. [83] This shows that ferroelastic superdomains move as large coherent blocks in ferroelectric switching [31,[84][85][86][87] and hence that the switching dynamics are not dominated by reversal of nano-scale ferroelectric domains within these blocks, i.e. are not described by the Landau-Lifshitz-Kittel domain model.…”

“…In addition to these two kinds of ferroelastic walls (mirror plane and twofold axis), more recently it has been shown that ferroelastic fourfold axes also exist. [44] These ferroelastic bundles switch as a block in some ferroelectrics, [45,46] resulting in hysteresis loops with very large steps. We emphasize this aspect of superdomains, because it will control ferroelectric switching in many thin-film devices, because most ferroelectric memory materials are also ferroelastic.…”