Physics:Flexoelectricity

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Short description: Polarization due to a strain gradient

Flexoelectricity is a property of a dielectric material where there is coupling between electrical polarization and a strain gradient. This phenomenon is closely related to piezoelectricity, but while piezoelectricity refers to polarization due to uniform strain, flexoelectricity specifically involves polarization due to strain that varies from point to point in the material. This nonuniform strain breaks centrosymmetry, meaning that unlike in piezoelectricity, flexoelectric effects occur in both centrosymmetric and asymmetric crystal structures.[1][2] This property is not the same as ferroelasticity. It plays a critical role in explaining many interesting electromechanical behaviors in hard crystalline materials and core mechanoelectric transduction phenomena in soft biomaterials.[3] Additionally, it is a size-dependent effect that becomes more significant in nanoscale systems,[4] such as crack tips.[5] Unlike piezoelectricity which only occurs in materials without inversion symmetry, flexoelectricity occurs in all dielectrics.[1][2]

In common usage, flexoelectricity is the generation of polarization due to a strain gradient; inverse flexoelectricity is when polarization, often due to an applied electric field, generates a strain gradient. Converse flexoelectricity is where a polarization gradient induces strain in a material.[6]

The electric polarization Pi due to a mechanical strain of ϵij in a dielectric is given by:

Pi=eijkϵjk+μijkl∂ϵjk∂xl

where the first term corresponds to the direct piezoelectric effect and the second term corresponds to the flexoelectric polarization induced by the strain gradient. The flexoelectric coefficient, μijkl, is a fourth-rank polar tensor and eijk is the coefficient corresponding to the direct piezoelectric effect.[1][2]

See also

References

  1. ↑ 1.0 1.1 1.2 Zubko, Pavlo; Catalan, Gustau; Tagantsev, Alexander K. (2013). "Flexoelectric Effect in Solids". Annual Review of Materials Research 43: 387–421. doi:10.1146/annurev-matsci-071312-121634. Bibcode: 2013AnRMS..43..387Z. 
  2. ↑ 2.0 2.1 2.2 Yudin, P V; Tagantsev, A K (2013-10-02). "Fundamentals of flexoelectricity in solids". Nanotechnology 24 (43). doi:10.1088/0957-4484/24/43/432001. ISSN 0957-4484. 
  3. ↑ Nguyen, Thanh D.; Mao, Sheng; Yeh, Yao-Wen; Purohit, Prashant K.; McAlpine, Michael C. (2013). "Nanoscale Flexoelectricity". Adv. Mater. 25 (7): 946–974. doi:10.1002/adma.201203852. PMID 23293034. Bibcode: 2013AdM....25..946N. 
  4. ↑ Wang, Bo; Gu, Yijia; Zhang, Shujun; Chen, Long-Qing (2019-12-01). "Flexoelectricity in solids: Progress, challenges, and perspectives". Progress in Materials Science 106: 100570. doi:10.1016/j.pmatsci.2019.05.003. ISSN 0079-6425. https://www.sciencedirect.com/science/article/pii/S0079642519300465. 
  5. ↑ Hongguang Wang, Xijie Jiang, Yi Wang, Robert W. Stark, Peter A. van Aken, Jochen Mannhart, Hans Boschker (2020). "Direct observation of huge flexoelectric polarization around crack tips". Nano Lett. 20 (1): 88–94. doi:10.1021/acs.nanolett.9b03176. PMID 31851827. Bibcode: 2020NanoL..20...88W. 
  6. ↑ "Converse flexoelectricity yields large piezoresponse force microscopy signals in non-piezoelectric materials.". Nature Communications 10 (1): 1266. 2019. doi:10.1038/s41467-019-09266-y. PMID 30894544. Bibcode: 2019NatCo..10.1266A. 



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