Periodic arrays of flux-closure domains in ferroelectric thin films with oxide electrodes

Abstract

Flux-closure domain structures in ferroelectric thin films are considered to have potential applications in electronic devices. It is usually believed that these structures are stabilized by the depolarization field and the contact with electrodes tends to screen the depolarization field and may limit their formation. In this work, the influence of oxide electrodes (SrRuO 3 and La 0.7 Sr 0.3 MnO 3) on the formation of flux-closure domains in PbTiO 3 thin films deposited on (110)-oriented GdScO 3 substrates by pulsed laser deposition was investigated by Cs-corrected transmission electron microscopy. It is found that periodic flux-closure domain arrays can be stabilized in PbTiO 3 films when the top and bottom electrodes are symmetric, while a/c domains appear when asymmetric electrodes are applied. The influence of asymmetric electrodes on the domain configuration is proposed to have a connection with their different work functions and conductivity types. These results are expected to shed light on understanding the nature of flux-closure domains in ferroelectrics and open some research possibilities, such as the evolution of these structures under external electric fields.

Metal–ferroelectric supercrystals with periodically curved metallic layers

“…In addition to the supercrystal phase, our experiments and simulations both reveal the coexistence of another domain structure, which does not lead to the doubling of the out-of-plane superlattice period. This domain structure gives rise to an additional set of satellites in X-ray diffraction measurements (Fig S8 ) and corresponds to arrays of zigzagging flux-closure domains that have previously been reported in other PbTiO 3 -based multilayers, 4,21,22 The stable modulated structure with controllable periodicity and a high density of domain walls observed in hierarchical PbTiO 3 /SrTiO 3 superlattices is likely to harbour unusual elastic and dielectric properties that warrant further exploration. Our phase-field simulations, summarised in Figure S12, show that application of an electric field leads to displacements of the 180° domain walls within the vertical flux closure regions, such that c-domains oriented parallel to the field grow at the expense of those aligned antiparallel to it.…”

Domain structure and dielectric properties of metal-ferroelectric superlattices with asymmetric interfaces

“…Direct imaging of the domains using scanning probe techniques is challenging due to their small sizes and buried nature, and it has been mainly restricted to ferroelectric-dielectric bilayers and trilayers, or superlattices with larger domains [22][23][24]. Recently, however, the complex polarization textures have been directly observed using transmission electron microscopy, revealing ordered flux-closure domains [25][26][27], as well as vortexlike and bubblelike structures with gradually curling polarization components and a macroscopic chirality observed by resonant x-ray diffraction [28][29][30][31].…”

“…However, experimentally, the presence of domains was usually inferred indirectly from studies of polarization dynamics [47], film tetragonality [48], macroscopic piezoresponse [49,50], or second-harmonic generation [51]. Recently, depolarization-induced polarization arrangements [52] and periodic flux-closure structures [27] have been observed directly in electroded PbTiO 3 films using transmission electron microscopy (TEM), but a systematic study of these domains, their scaling with ferroelectric thickness, and their effect on the macroscopic properties is still lacking.…”

Atomic-scale observations of electrical and mechanical manipulation of topological polar flux closure

“…skyrmions) have shown great potential applications in electromechanical devices 1 , spintronic information storage devices 2,3 and logic devices [4][5][6] due to their topologically protected states 7 . Given the similarities between ferromagnetism and ferroelectricity, the complex lowdimensional topological polar structures that inherent to ferroelectric materials, such as polar flux-closure 8,9 and vortex 10,11 , have also been attracting increasing attentions in recent years 1,8,9,[11][12][13][14][15] . Polar flux-closure is a stable topological domain structure formed by the interplay of charge, orbital, and lattice degrees of freedom, with head-to-tail continuous electric dipoles 8,16,17 .…”

“…Topological structures in ferromagnetic materials (e.g., skyrmions) have shown great potential for application to electromechanical devices ( 1 ), spintronic information storage devices ( 2 , 3 ) and logic devices ( 4 – 6 ) owing to their topologically protected states ( 7 ). Given the similarities between ferroelectricity and ferromagnetism, the complex low-dimensional topological polar structures that are inherent to ferroelectric materials, such as quadrant domains ( 8 ), polar flux-closures ( 9 , 10 ), and vortices ( 11 , 12 ), have also been attracting increasing attentions in recent years ( 1 , 9 , 10 , 12 – 16 ). A polar flux-closure is a stable topological domain structure formed mainly by the interplay between a depolarization field and mechanical boundary conditions ( 1 , 17 – 21 ) and consisting of short segmented 90° and 180° domain walls ( 9 , 22 ).…”