Direct imaging of the spatial and energy distribution of nucleation centres in ferroelectric materials

Abstract

Macroscopic ferroelectric polarization switching, similar to other first-order phase transitions, is controlled by nucleation centres. Despite 50 years of extensive theoretical and experimental effort, the microstructural origins of the Landauer paradox, that is, the experimentally observed low values of coercive fields in ferroelectrics corresponding to implausibly large nucleation activation energies, are still a mystery. Here, we develop an approach to visualize the nucleation centres controlling polarization switching processes with nanometre resolution, determine their spatial and energy distribution and correlate them to local microstructure. The random-bond and random-field components of the disorder potential are extracted from positive and negative nucleation biases. Observation of enhanced nucleation activity at the 90 composite function domain wall boundaries and intersections combined with phase-field modelling identifies them as a class of nucleation centres that control switching in structural-defect-free materials.

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

“…2b, a new À c-domain (where the negative sign indicates downward polarization) nucleates and grows at the top interface at a bias of 8.2 V, leading to the contrast change from bright to dark. Although previous studies proposed that the nucleation of c-domains preferentially begins from 90°domain walls 3,8,15 , our in situ TEM observations revealed that nucleation occurs only at the top interface with a negative bias 5,10 . The switched À c-domain grew with increasing voltage (Fig.…”

“…An understanding of the local response and underlying dynamic behaviour of individual domain walls and defects throughout the thickness of the film during the switching process is necessary, however, to engineer reliable ferroelectric devices [6][7][8][9][10][11][12][13][14] . This is especially important in ferroelectric memory devices scaled down to the nanometre scale to achieve a high data storage density where a single defect may dominate the total switching process.…”

Single ferroelectric-domain photovoltaic switch based on lateral BiFeO3 cells

“…25,26 In perovskite oxides, it is known that mobile V O 2 þ ions tend to occupy thermodynamically preferential sites in extended crystal defects, such as DWs, grain boundaries and dislocations. [27][28][29][30][31][32][33][34] Often, these vacancies modify local cation valences and displacements and act as wall-pinning centers. 35 In turn, they contribute to diffusive photovoltaic switching in our multidomain BFO channels, as shown in Figures 5b and d.…”

High-Resolution Studies of Domain Switching Behavior in Nanostructured Ferroelectric Polymers

“…There is a large amount of experimental evidence that both switching mechanisms are strongly affected by the defect structure of the ferroelectric medium. 3,4 Domain wall creep has been observed in the disordered systems with longrange variations in pinning potential (so-called random field disorder) with the wall velocity obeying an exponential field dependence, while the short-range (random bond) disorder leads to a power law dependence. 5,6 Dissimilar distribution functions of switching times in ferroelectric films with different microstructure are the root cause for qualitatively different time-dependent switching behavior described either by the statistical Kolmogorov−Avrami−Ishibashi model 7,8 or nucleation limited kinetics.…”