At high electric fields, the electrical energy stored in a soft elastomer dielectric can be comparable
to the mechanical deformation energy it produces. This has led to the development of a class
of electrically controlled, large strain dielectric elastomer actuators for soft robotics and energy
harvesting devices. At large electric fields, the electro-mechanically induced deformation can lead
to pseudo-periodic surface morphological instabilities which then grow with increasing field into
stable pre-breakdown defects prior to final, irreversible electrical breakdown. Under these extremes
of combined large electrical and mechanical deformations, the morphological evolution of the prebreakdown
defects has not hitherto been reported. In contrast to the filamentary breakdown of much
stiffer dielectrics, fluorescence confocal microscopy reveals an array of defects that evolve through
a complex, reversible series of morphologies, transitioning from axi-symmetric ‘‘pits’’ to ‘‘crack-like’’
shapes that can ‘‘twist’’ and deflect, and finally open to form an array of holes. The observations suggest
that the transitions, from axi-symmetric pits to flat, slit-like defects and then to an array of holes,
are geometric instabilities. The implications for using a soft elastomer layer to increase the dielectric
breakdown of a stiffer dielectric are discussed.
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Colossal flexoresistance in dielectrics
Abstract Dielectrics have long been considered as unsuitable for pure electrical switches; under weak electric fields, they show extremely low conductivity, whereas under strong fields, they suffer from irreversible damage. Here, we show that flexoelectricity enables damage-free exposure of dielectrics to strong electric fields, leading to reversible switching between electrical states—insulating and conducting. Applying strain gradients with an atomic force microscope tip polarizes an ultrathin film of an archetypal dielectric SrTiO 3 via flexoelectricity, which in turn generates non-destructive, strong electrostatic fields. When the applied strain gradient exceeds a certain value, SrTiO 3 suddenly becomes highly conductive, yielding at least around a 10 8 -fold decrease in room-temperature resistivity. We explain this phenomenon, which we call the colossal flexoresistance, based on the abrupt increase in the tunneling conductance of ultrathin SrTiO 3 under strain gradients. Our work extends the scope of electrical control in solids, and inspires further exploration of dielectric responses to strong electromechanical fields.
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- Award ID(s):
- 1744213
- NSF-PAR ID:
- 10288188
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-020-16207-7
