Thermal quench effects on ferroelectric domain walls

Abstract

Using piezoresponse force microscopy on epitaxial ferroelectric thin films, we have measured the evolution of domain wall roughening as a result of heat-quench cycles up to 735• , with the effective roughness exponent ζ changing from 0.25 to 0.5. We discuss two possible mechanisms for the observed ζ increase: a quench from a thermal 1-dimensional configuration, and from a locallyequilibrated pinned configuration with a crossover from a 2-to 1-dimensional regime. We find that the post-quench spatial structure of the metastable states, qualitatively consistent with the existence of a growing dynamical length scale whose ultra slow evolution is primarily controlled by the defect configuration and heating process parameters, makes the second scenario more plausible. This interpretation suggests that pinning is relevant in a wide range of temperatures, and in particular, that purely thermal domain wall configurations might not be observable in this glassy system. We also demonstrate the crucial effects of oxygen vacancies in stabilizing domain structures.

Nonsteady relaxation and critical exponents at the depinning transition

“…From a purely theoretically point of view, considerable progress has been made in recent years thanks to a fruitful interplay between the very powerful analytical [3][4][5] and numerical techniques specially developed for studying equilibrium [6,7], depinning [8][9][10][11][12], and creep [13,14] of strictly elastic manifolds. From the experimental viewpoint, on the other hand, the understanding of this particular problem is directly relevant for various experimental situations where the elastic approximation is well met, such as magnetic [15][16][17][18] or ferroelectric domain walls [19][20][21][22], contact lines in wetting [23,24], and fractures [25,26]. It has also been useful for making a connection between laboratory friction experiments and the observed spatial and temporal earthquake clustering [27].…”

Effect of thermal annealing on ferroelectric domain structures in poly(vinylidene-fluoride-trifluorethylene) Langmuir-Blodgett thin films

“…Such temperature-independent DW roughness is in sharp contrast with what has been previously reported for ferroelectric PZT thin films, where f increases from 0.26 at room temperature to 0.5 after the samples have been heated close to T C . 22,27 The change of the roughness exponent in PZT has been attributed to a DW dimensionality crossover from 2D to 1D as the dynamical length scale of the DW grows at elevated temperatures and becomes comparable with the film thickness. 22 Unlike PZT thin films, the LB copolymer films exhibit thickness-independent 2D ferroelectricity, and the DW is intrinsically one-dimensional.…”

“…Stripe-shape domain structures were written at room temperature and subjected to thermal annealing at progressively higher temperatures up to the ferroelectric Curie temperature T C of approximately 110 C. The static configuration of the domain walls (DWs) does not exhibit appreciable changes in characteristics after thermal annealing, showing an temperature-independent roughness exponent f of 0.4-0.5, which is qualitatively different from what has been observed in ferroelectric oxides. 22 As the samples were annealed at temperatures close to T C , we observed spontaneous polarization reversal in randomly scattered sites for both polarization states, with the number of domain nucleation sites increasing with increasing temperature. We extracted the fraction of the switched area as a function of annealing temperature and discussed the difference in the relevant energy scales for domain formation between ferroelectric polymers and oxides, which can lead to their different responses to thermal annealing.…”

Thickness scaling of ferroelastic domains in PbTiO3 films on DyScO3

“…30 Indeed, it rather looks like we are seeing a law that differs from that predicted by equilibrium models, something unsurprising for such fast-grown films.…”