Flexoelectric effect in elastomers

Marvan, M.; Havránek, A.

doi:10.1007/bfb0114342

Cited by 82 publications

(56 citation statements)

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“…However, as will be discussed later in this paper, it should be noted that the flexoelectric coupling mechanism of self-polarization can work at temperatures well above the Curie transition point T c while the piezoelectric mechanism cannot. As shown in Table 1, flexoelectric response in ferroelectrics [5][6][7][8][9][10] is much greater than those in simple dielectrics [1][2][3]23], the measured µ 12 coefficients at 25 °C range from 3.4 µC/m for PbMg 1/3 Nb 2/3 O 3 (PMN) to 76.5 µC/m for Ba 0.67 Sr 0.33 TiO 3 (BST), as a comparison, the coefficients for simple dielectrics are only of the order of 10 -10 C/m. Based on direct flexoelectricity, novel piezoelectric composites might be developed, where all the components are non-piezoelectric, but external mechanical loading leads to strain gradients that result in electric polarization in the properly-shaped components [24].…”

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A study of flexoelectric coupling associated internal electric field and stress in thin film ferroelectrics

Ma¹

2008

Physica Status Solidi (b)

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By discussions in the framework of tensor representations and phenomenological theory, general piezoelectricity equations that incorporate direct and inverse flexoelectric effects were analyzed and interlink between direct and inverse flexoelectricity discovered. Due to flexoelectric coupling, mechanical strain gradient is equivalent to internal electric field. In ferroelectrics above the Curie temperature, it was shown theoretically that strain gradient associated electric field leads to non‐zero polarization without external electric field. It was also shown theoretically that polarization (or electric field) gradient is an extra source of internal stress. Magnitudes of flexoelectricity associated internal electric field and stress were analyzed for heteroepitaxial thin films of barium strontium titanate. Flexoelectric coupling is expected to intensify with reducing lateral dimensions and thickness and get large enough at nanoscale to modify ferroelectric phase transitions and functional response. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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A study of flexoelectric coupling associated internal electric field and stress in thin film ferroelectrics

Ma¹

2008

Physica Status Solidi (b)

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“…[22][23][24] The investigation of flexoelectricity has been mainly focused on inorganic materials and there has been relatively little work reported on soft materials like polymers. [25][26][27] In a prior report, 28 we described a procedure to determine the true flexoelectric response in ferroelectric polymer thin films by minimizing and correcting for piezoelectric contributions. Most notably, the flexoelectric response in three distinct states-ferroelectric, paraelectric, and relaxor-was compared.…”

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Temperature dependence of flexoelectric response in ferroelectric and relaxor polymer thin films

Poddar

Ducharme

2014

Journal of Applied Physics

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We report the temperature dependence of the flexoelectric response in thin films of both ferroelectric and relaxor forms of vinylidene fluoride polymers. The ferroelectric samples were depoled to minimize piezoelectric response by heating them beyond their Curie temperature and then cooling in zero applied electric field. In both the relaxor ferroelectric polymer and the paraelectric state of the ferroelectric copolymer, the flexoelectric coefficient was proportional to the dielectric constant over a limited range of temperatures, in agreement with general theoretical principles. The enhancements in flexoelectric response were also observed near the Curie transition temperature for the ferroelectric polymer and near the dielectric relaxation temperature for the relaxors. The broad dielectric anomaly in these systems provides greater temperature stability for these enhancements.

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“…[4][5][6] In liquid crystals, 7 upon application of a strain gradient, the ordering of the large bulky molecules is strongly dependent on the shape anisotropy of the molecular species. In the case of polymers, [8][9][10][11] and elastomers, 12 the ordering of the polymer chains depends on the size and rigidity of the side groups and cross-linked functional groups. While in inorganic amorphous materials, 13 a distortion in the random network of local bonding units renders the system polar.…”

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“…He showed that such inhomogeneous deformation potentials would polarize the medium even for centrosymmetric crystals and estimated the flexoelectric coefficient to be of the order of 0.1 nC/m. Marvan's work with the elastomers 12 considered a model of dipolar reorientation in anisotropic free volume to give an order of magnitude estimate of the flexoelectric coefficient between 0.1 nC/m and 1 nC/m. In a later theoretical work based on a rigid ion model, Tagantsev showed that the flexoelectric coefficient should also be proportional to the dielectric constant of the material since a high dielectric constant leads to larger ionic polarizability.…”

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Finite-size scaling of flexoelectricity in Langmuir-Blodgett polymer thin films

Poddar

Foreman

Adenwalla

et al. 2016

Applied Physics Letters

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The flexoelectric effect, which is a linear coupling between a strain gradient and electrical polarization, is a fundamental electromechanical property of all materials with potential for use in nanoscale devices, where strain gradients can be quite large. We report a study of the dependence of the flexoelectric response on thickness in ultrathin films of polar and non-polar polymers. The measurements of the flexoelectric response in non-polar polyethylene and the polar relaxor polymer polyvinylidene-co-trifluoroethylene-co-chlorofluoroethylene were made using a bent cantilever method and corrected for the contribution from the electrode oxide. The results show that the value of the flexoelectric coefficient increases with decreasing thickness, by up to a factor of 70 compared to the bulk value, reaching such enhanced values in films of only 10 nm thickness. These results are consistent with a model accounting for interfacial contributions, and underline how large electromechanical coupling can be produced at the nanoscale. The results also distinguish the surface flexoelectric response from that coming from the volume.

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Flexoelectric effect in elastomers

Cited by 82 publications

References 1 publication

A study of flexoelectric coupling associated internal electric field and stress in thin film ferroelectrics

A study of flexoelectric coupling associated internal electric field and stress in thin film ferroelectrics

Temperature dependence of flexoelectric response in ferroelectric and relaxor polymer thin films

Finite-size scaling of flexoelectricity in Langmuir-Blodgett polymer thin films

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