Abstract
The interconversion between electrical and mechanical energies is pivotal to ferroelectrics to enable their applications in transducers, actuators and sensors. Ferroelectric polymers exhibit a giant electric-field-induced strain (>4.0%), markedly exceeding the actuation strain (≤1.7%) of piezoelectric ceramics and crystals. However, their normalized elastic energy densities remain orders of magnitude smaller than those of piezoelectric ceramics and crystals, severely limiting their practical applications in soft actuators. Here we report the use of electro-thermally induced ferroelectric phase transition in percolative ferroelectric polymer nanocomposites to achieve high strain performance in electric-field-driven actuation materials. We demonstrate a strain of over 8% and an output mechanical energy density of 11.3 J cm−3 at an electric field of 40 MV m−1 in the composite, outperforming the benchmark relaxor single-crystal ferroelectrics. This approach overcomes the trade-off between mechanical modulus and electro-strains in conventional piezoelectric polymer composites and opens up an avenue for high-performance ferroelectric actuators.
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Data availability
The main data supporting the findings of this study are available within this Article and its Supplementary Information. The Source Data that support the findings of this study are publicly available via figshare at https://doi.org/10.6084/m9.figshare.22677616. Source data are provided with this paper.
Code availability
Quantum ESPRESSO for DFT calculations is available at https://www.quantum-espresso.org/. The atomic coordinates of the optimized computational models are publicly available via figshare at https://doi.org/10.6084/m9.figshare.22677616.
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Acknowledgements
This research was funded by the US AFOSR (FA9550-19-1-0008 to Q.W.), the US ONR (N00014-19-1-2033 to J.B.), the National Natural Science Foundation of China (12274152 to Y.L.) and initial financial support from HUST (3004110155 to Y.L.). The phase-field simulation effort was supported as part of the Computational Materials Sciences Program funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (award no. DE-SC0020145 to T.Y. and L.-Q.C.), and the Mu-PRO Ferroelectric software package was used. The atomistic calculations were performed at Oak Ridge Leadership Computing Facility, supported by DOE contract DE-AC05-00OR22725.
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Y.L. and Q.W. conceived and designed the research. Y.L. and Y.Z. prepared the samples. Y.L., Y.Z. and X.C. conducted the electrical and electromechanical measurements. Y.L. and X.C. collected the XRD and FTIR data under an electric field. Y.L. performed the temperature-dependent XRD and dielectric measurements. Y.L. and Y.Z. performed the AFM-IR measurements. Y.L. and X.C. measured the Joule heating, temperature change and fatigue tests. Y.Z. performed the DSC and piezoelectric measurements. Y.Z., X.C. and Z.H. performed the blocking force and strain–frequency measurements. L.L. and K.W. carried out the transmission electron microscopy measurements. H.Q., B.Z., W.L. and J.B. performed and analysed the DFT calculations. T.Y. and L.-Q.C. performed and analysed the phase-field simulations. Y.L., Y.Z. and Q.W. wrote the manuscript with input from all authors. Q.W. supervised the research.
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Nature Materials thanks Chris Bowen, Senentxu Lanceros-Méndez and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data
Extended Data Fig. 1 Strain-electric field loops of the PVDF/TiO2 nanocomposites with different TiO2 contents under various bipolar electric fields at 1 Hz.
a, 0 vol%. b, 2.1 vol%. c, 4.3 vol%. d, 9.3 vol%. e, 12.0 vol%. f, 14.9 vol%. g, 21.4 vol%.
Extended Data Fig. 2 Electrical conduction of the PVDF/TiO2 nanocomposites.
a, Conduction current density of the PVDF/TiO2 nanocomposites under 10 MV m−1 electric field. b, TiO2 content-dependent conductivity of the PVDF/TiO2 nanocomposites. The red line is the fitting of the conductivity by the percolation model, which gives a percolation threshold (fc) of about 15 vol% as indicated by the blue line.
Extended Data Fig. 3 Temperature-dependent dielectric spectra of the PVDF/TiO2 nanocomposites with different TiO2 contents at 1 kHz.
a, Dielectric constant. b, Dissipation factor. The red arrows indicate the electro-thermal phase transition temperature of about 29 °C.
Extended Data Fig. 4 Comparison of different types of phase transitions in ferroelectric polymers.
Top panel: a typical ferroelectric-to-paraelectric phase transition is characterized by a structure change from orthorhombic phase to hexagonal phase, which can be triggered by heating above the Curie temperature. The application of an electric field always favors the orthorhombic ferroelectric phase. In the low field regime (≤50 MV m−1), only piezoelectricity or electrostriction contributes to the strain response. Bottom panel: electro-thermal phase transition corresponds to phase switching from orthorhombic phase to monoclinic phase induced by directly heating or the Joule heat from the applied electric field. Here, an electric field may stabilize the monoclinic nonpolar phase rather than the orthorhombic polar phase. The electric field can be as low as around 40 MV m−1 in percolative polymer nanocomposites.
Extended Data Fig. 5 Unipolar and frequency-dependent strain of the percolative PVDF/TiO2 nanocomposites (=14.9 vol%).
a, Comparison of the strain-electric field loops of the percolative PVDF/TiO2 nanocomposite under 40 MV m−1 bipolar and unipolar electric field. b, Frequency-dependent strain of the percolative PVDF/TiO2 nanocomposite. Error bars represent the standard deviation of the mean obtained from at least three measurements using different samples.
Extended Data Fig. 6 Temperature changes in PVDF and percolative PVDF/TiO2 nanocomposite (\(\bf {c}_{{{\rm{TiO}}}_{2}}\) = 14.9 vol%).
The temperature change is generated due to Joule heating upon the application of an electric field of 40 MV m−1.
Extended Data Fig. 7 Electro-thermal actuation of the PVDF/ZnO nanocomposites.
a, Strain of the PVDF/ZnO nanocomposites under various bipolar electric fields at 1 Hz. Error bars represent the standard deviation of the mean obtained from at least three measurements using different samples. b-h, Strain-electric field loops of the PVDF/ZnO nanocomposites with the ZnO content of 0 vol% (b), 2.1 vol% (c), 4.3 vol% (d), 9.3 vol% (e), 12.0 vol% (f), 14.9 vol% (g) and 21.4 vol% (h) under various bipolar electric fields at 1 Hz.
Extended Data Fig. 8 Electro-thermal actuation of the P(VDF-HFP)/TiO2 nanocomposites.
a, Strain of the P(VDF-HFP)/TiO2 nanocomposites under various bipolar electric fields at 1 Hz. Error bars represent the standard deviation of the mean obtained from at least three measurements using different samples. b, Strain-electric field loops of the P(VDF-HFP)/TiO2-14.9 vol% nanocomposite under various bipolar electric fields at 1 Hz.
Extended Data Fig. 9 Temperature-dependent strain upon heating.
a, PVDF/ZnO. b, PVDF/TiO2-nanowires. c, P(VDF-HFP)/TiO2. The thermally-induced strain in PVDF/ZnO, PVDF/TiO2-nanowires and P(VDF-HFP)/TiO2 is 5.4%, 0.28% and 3.9%, which are consistent well with the electric field-induced strain triggered by Joule heating of 5.3%, 0.21% and 3.7%, respectively.
Supplementary information
Supplementary Information
Supplementary Figs. 1–16, Notes 1–3, Tables 1 and 2 and references 1–13.
Source data
Source Data Fig. 4
Local IR data (Fig. 4c,d).
Source Data Extended Data Fig. 1
Strain–electric field data (Extended Data Fig. 1a–g).
Source Data Extended Data Fig. 6
Temperature change data (Extended Data Fig. 6).
Source Data Extended Data Fig. 9
Temperature-dependent strain data (Extended Data Fig. 9a–c).
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Liu, Y., Zhou, Y., Qin, H. et al. Electro-thermal actuation in percolative ferroelectric polymer nanocomposites. Nat. Mater. (2023). https://doi.org/10.1038/s41563-023-01564-7
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DOI: https://doi.org/10.1038/s41563-023-01564-7
