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J. Hafner, S. Benaglia, F Richheimer, M. Teuschel, F. Maier, W. Artner, S. Wood, D. Platz, M. Schneider, K. Hradil, F. Castro, R. Garcia, U. Schmid:
"Multi-scale characterisation of a ferroelectric polymer reveals the emergence of a morphological phase transition driven by temperature";
Nature Communications, 12 (2021), Artikel 152; 1 - 9.

Ferroelectric materials exhibit a phase transition to a paraelectric state driven by temperature
- called the Curie transition. In conventional ferroelectrics, the Curie transition is caused by a
change in crystal symmetry, while the material itself remains a continuous three-dimensional
solid crystal. However, ferroelectric polymers behave differently. Polymeric materials are
typically of semi-crystalline nature, meaning that they are an intermixture of crystalline and
amorphous regions. Here, we demonstrate that the semi-crystalline morphology of the fer-
roelectric copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) strongly
affects its Curie transition, as not only a change in crystal symmetry but also in morphology
occurs. We demonstrate, by high-resolution nanomechanical measurements, that the semi-
crystalline microstructure in the paraelectric state is formed by crystalline domains
embedded into a softer amorphous phase. Using in situ X-ray diffraction measurements, we
show that the local electromechanical response of the crystalline domains is counterbalanced
by the amorphous phase, effectively masking its macroscopic effect. Our quantitative multi-
scale characterisations unite the nano- and macroscopic material properties of the ferro-
electric polymer P(VDF-TrFE) through its semi-crystalline nature.

http://dx.doi.org/10.1038/s41467-