Understanding discrepancies in flexoelectric behavior can open the door to further applications

Flexoelectricity, the coupling between the electric polarization of a material and the strain gradient applied to it, is an important property in the development of functional materials with applications ranging from sensing to electronic transport. However, while flexoelectricity is typically thought of as a linear effect, this is only true at low strain gradients. In order to resolve the dichotomy between macroscale and nanoscale flexoelectricity, Wang et al. studied how its behavior changes with the applied strain in three different materials.

“The design and application of flexoelectric micro/nano devices are rare,” said author Wenbin Huang. “This is attributed to the lack of the understanding of the flexoelectric coefficients at different scales.”

The researchers found a saturation effect in flexoelectricity as the strain gradient increases past a critical threshold value, leading to a nonlinear declining effect for larger strain gradients. They propose modelling the relationship between the strain gradient and flexoelectric coefficient as a logarithmic relationship, satisfying the change in behavior between nano and macroscales.

“When a very large strain gradient is generated in those micro/nano flexoelectric structures, if we still use the flexoelectric coefficient characterized under the small strain gradient, serious errors could occur,” Huang said. Without understanding the source of these errors, technologies that utilize the flexoelectric behavior cannot be developed.

To study this, the authors applied large strain gradients to three different materials until they approached their breaking point and collected the electric charge outputted by the materials to obtain the flexoelectric polarization.

They note this is just the first step in studying flexoelectric nonlinearity. Once they better understand this phenomenon, they hope to apply material engineering approaches to tune nonlinear flexoelectricity for potential applications.

Source: “Non-linear behavior of flexoelectricity,” by Zhiguo Wang, Ruobing Song, Zhenjiang Shen, Wenbin Huang, Chunchun Li, Shanming Ke, and Longlong Shu, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5126987 .