Flexoelectric materials, structures, micro/nanofabrication and devices

Flexoelectric materials characterization

Flexoelectricity is the coupling between dielectric polarization and strain gradient. Different from piezoelectricity, which only exist in ferroelectric phases of 20 crystal symmetry groups, flexoelectricity is possessed by all insulate solids in both ferroelectric and paraelectric phases. High-permittivity materials like BaxSr1-xTiO3 (BST) are found to have much larger flexoelectric properties compared with other solid materials.

u12d33

Left: Transverse flexoelectric coefficients of BST with different thicknesses; Right: Comparison of effective d33values of flexoelectric cantilever with piezoelectric counterparts as a function of thickness.

u44

Electric field gradient distribution in a pyramid structure.

Flexoelectric structural health monitoring

Strain gradient is regarded as a better indicator of the structural health than mechanical deformation or strain at some circumstances. When stress concentration occurs, e.g. near the hole structures or cracks, strain has a rapid change in a small distance, leading to a large strain gradient. A novel flexoelectric strain gradient sensor (SGS) based on BST microbar was designed and developed to monitor the strain gradient information in the mechanical structure. SGS was demonstrated to be capable of measuring the curvature of the shell structure. It was also applied to measure the openning mode stress intensity factor of the cracked structure.

crackcrack-1

SGS for measuring the openning mode stress intensify factor of cracked structure.

Flexoelectric sensing

Attributed to the scale effect of flexoelectricity, miniacturized flexoelectric structures could be used for many sensing applications by providing higher sensitivty and more materials choices. Flexoelectric accelerometer and microphone were succesfully developed using flexoelectric beam structures, which could achieve a relative high sensitivty and broad bandwidth at the same time.

microphone-1microphone-2

Flexoelectric microphone and frequency response.

References:

  1. Kwon, S.R.,W. Huang, S. Zhang, F.-G. Yuan and X. Jiang, “Study on a flexoelectric microphone using barium strontium titanate“, Journal of Micromechanics and Microengineering, 26(4), 045001 (2016).
  2. Kwon, S.R., W. Huang, L. Shu, F.G. Yuan, J.P. Maria, X. Jiang, “Flexoelectricity in Barium Strontium Titanate Thin Film“, Applied Physics Letters, 105(14), 142904 (2014).
  3. Shu, L., F. Li, W. Huang, X. Wei, X. Yao, X. Jiang, “Relationship between Direct and Converse Flexoelectric Coefficients“, Journal of Applied Physics, 116(14), 144105 (2014).
  4. W. Huang, S. Yang, N. Zhang, F.-G. Yuan, and X. Jiang, “Direct measurement of opening mode stress intensity factors using flexoelectric strain gradient sensors“, Experimental Mechanics, 55(2), 313-320 (2014).
  5. Shu, L.,  W. Huang, S. Kwon, Z.  Wang, F. Li, X.  Wei, S. Zhang, M.  Lanagan, X. Yao, X.  Jiang, “Converse flexoelectric coefficient f1212 in bulk Ba0.67Sr0.33TiO3”, Applied Physics Letters, 104(23), 232902 (2014).
  6. Huang, W., S.-R. Kwon, S. Zhang, F.-G. Yuan, X. Jiang, “A trapezoid shape flexoelectric accelerometer“, Journal of Intelligent Material Systems and Structures, 25(3), 271-277 (2014).
  7. Kwon, S.R, W. Huang, F.-G. Yuan, X.N. Jiang, “Flexoelectric sensing using a multilayered barium strontium titanate structure“, Smart Materials and Structures, 22(11), 115017 (2013).
  8. Yan, X., W. Huang, S.R. Kwon, S. Yang, X. Jiang, F.-G. Yuan, “A sensor for the direct measurement of curvature based on flexoelectricity“, Smart Materials and Structures, 22(8) 085016 (2013).
  9. Yan, X., W. Huang, S.R. Kwon, S. Yang, X. Jiang, F.-G. Yuan, “A sensor for the direct measurement of curvature based on flexoelectricity“, Smart Materials and Structures, 22, 085016 (2013).
  10. Huang, W., S.-R. Kwon, S. Zhang, F.-G. Yuan, X. Jiang, “A Trapezoid Shape Flexoelectric Accelerometer“, J Intel Mat Syst Str, (2013).
  11. Huang, W.B., X. Yan, S. Kwon, S. Zhang, F. Yuan and X.N. Jiang, “Ba0.64Sr0.36TiO3 (BST) flexoelectric sensing for strain gradient detection” , Appl Phys Lett, 101, 252903 (2012).
  12. Huang, W., X. Yan, S.R. Kwon, S. Zhang, F.G. Yuan, X. Jiang, “Flexoelectric strain gradient detection using Ba0.64Sr0.36TiO3 (BST) for sensing“, Applied Physics Letters, 101(25), 252903 (2012).
  13. Huang, W., K. Kim, S. Zhang, F. Yuan and X.N. Jiang, “Scaling Effect of Flexoelectric (Ba,Sr)TiO3Microcantilevers”, Phys. Status Solidi RRL 5, No.9, pp. 350-352 (2011).

 

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MAE, NCSU, RALEIGH, NC