Mechanical Softness of Ferroelectric 180° Domain Walls

Abstract

Using scanning probe microscopy, we measure the out-of-plane mechanical response of ferroelectric 180°domain walls and observe that, despite separating domains that are mechanically identical, the walls appear mechanically distinct-softer-compared to the domains. This effect is observed in different ferroelectric materials (LiNbO 3 , BaTiO 3 , and PbTiO 3) and with different morphologies (from single crystals to thin films), suggesting that the effect is universal. We propose a theoretical framework that explains the domain wall softening and justifies that the effect should be common to all ferroelectrics. The lesson is, therefore, that domain walls are not only functionally different from the domains they separate, but also mechanically distinct.

Activation of nominally silent domain wall-localized phonons from GHz to THz frequencies

“…The low frequency of sliding modes is also behind the giant enhancement of the static dielectric permittivity [19]. In addition, soft DW phonons are responsible for mechanical softening phonomena, recently observed in several ferroelectrics [25].…”

Unveiling Alternating Current Electronic Properties at Ferroelectric Domain Walls

“…[31,32] Based on the emergent physical properties at ferroelectric domain walls, first test devices have been realized and their basic functionality has been demonstrated in proof-of-concept studies, including nonvolatile memory, [12,[33][34][35] switches, [36][37][38] diodes, [39] electronic power conversion, [23,37] and memristors. [40,41] Going beyond the unusual electronic response at domain walls, their dielectric, [42][43][44] piezoelectric, [43,45,46] and mechanical properties [47] have drawn attention. In addition, local photovoltaic effects, [48][49][50][51] magnetoresistive properties, [52][53][54] static negative capacitance, [55] and the possibility to control the propagation of phonons and heat flux [56][57][58] have been investigated.…”

Roadmap for Ferroelectric Domain Wall Nanoelectronics

“…Domain walls are also shown to act as functional electronic nanodevices including an electronic switch, [ 93 ] half‐wave rectifiers, [ 94 ] and memristors. [ 95,96 ] Moreover, there is now mounting experimental evidence suggesting that domain walls display not only distinct electronic properties but also coupled optical, [ 26–28 ] mechanical, [ 29 ] thermal, [ 30,31 ] and magnetic [ 32–34 ] (in multi‐ferroics) properties.…”

“…[ 24,25 ] Over the past decade, experimental and theoretical studies [ 11,12,14–19 ] investigating ferroelectric domain walls, the atomically sharp topological interfaces, across which the polarization reorients, have cast ferroelectrics in a completely new light. It is because ferroelectric domain walls have been found to display functional properties that do not exist anywhere in the bulk and parent domain wall‐free materials; these include electronic, [ 17–19,26–28 ] mechanical, [ 29 ] thermal, [ 30,31 ] and magnetic properties. [ 32–34 ]…”

“…Distinct functional‐property confinement at ferroelectric domain walls which is typically only about a nanometer wide, for example, electrical conduction, offers a novel paradigm for highly miniaturized low‐energy electronics. [ 11,12,14–19,26–34 ] For instance, a memory device that offers a new data storage principle where data is stored and processed by the domain walls can be conceived ( Figure , top). The encoded information is defined by the presence or absence of domain walls in the memory cell consisting of a ferroelectric mesa (thin film) sandwiched between two metal contacts.…”