Enhanced flexoelectric-like response in oxide semiconductors

Abstract

Flexoelectricity is a property of all dielectric materials whereby they polarize in response to deformation gradients such as those produced by bending. Although it is generally thought of as a property of dielectric insulators, insulation is not a formal requirement: in principle, semiconductors can also redistribute their free charge in response to strain gradients. Here we show that bending a semiconductor not only generates a flexoelectric-like response, but that this response can in fact be much larger than in insulators. By doping single crystals of wide-bandgap oxides to increase their conductivity, their effective flexoelectric coefficient was increased by orders of magnitude. This large response can be explained by a barrier-layer mechanism that remains important even at the macroscale, where conventional (insulator) flexoelectricity otherwise tends to be small. Our results open up the possibility of using semiconductors as active ingredients in electromechanical transducer applications.

Giant linear strain gradient with extremely low elastic energy in a perovskite nanostructure array

“…Future studies on BiFeO 3 and other perovskite materials nanostructures as flexible electronics, electromechanical or photoelectric devices could thus be stimulated. It is worthwhile to mention that, although flexoelectricity is generally discussed in terms of dielectric insulators, a very recent study by a three-point bending reveals that the flexoelectric-like coupling is much larger in doped oxide semiconductors than in dielectric insulators56. Thus, we propose that, by using doped lead-free perovskite oxides, it is possible to construct nanostructures with giant linear strain gradient where the flexoelectric-like behaviours could be further enhanced for electromechanical applications.…”

The surface mechanism for the flexoelectric response in sodium bismuth titanate‐based ferroelectric ceramics

“…By exploiting the flexoelectric effect, some novel devices, such as the memory devices in which information can be written mechanically and the flexoelectric piezoelectric composites, can be designed . Because of the importance of the flexoelectric effect in understanding various physical phenomena and the potential applications in novel functional devices, the research related to flexoelectric effect has received increasing attention in recent years …”

“…It is widely believed the large µ ij of the ferroelectrics is mainly from some extrinsic mechanisms rather than the intrinsic lattice mechanism. Different extrinsic mechanisms, such as the piezoelectric response caused by the inhomogeneity produced during the material processing, the barrier layer mechanism, and the residual ferroelectricity, have been proposed to explain the large discrepancy between the experimental µ ij and the theoretical value in ferroelectric materials, but the issue has not been completely resolved …”

Enabling nanoscale flexoelectricity at extreme temperature by tuning cation diffusion

“…Flexoelectricity has been first studied in liquid crystals 7 and has recently gained widespread interest for a broad range of material classes like ferroelectrics 8,9 , semiconductors 10 and biomaterials 11 . Many electromechanical 8,12,13 and memory 9 devices have been realized using the flexoelectric effect.…”