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J. Hafner, S. Benaglia, M. Teuschel, D. Platz, M. Schneider, R. Garcia, U. Schmid:
"Multi-scale characterisation of a semi-crystalline polymer reveals hidden ferroelectricity above the Curie transiton";
Talk: 8th Multifrequency AFM conference, Madrid; 10-27-2020 - 10-30-2020; in: "8th Multifrequency AFM conference, Book of Abstracts", (2020), 107.

Ferroelectrics exhibit a phase transition to a paraelectric state driven by temperature - called the
Curie transition. It is known that a ferroelectric material shows piezoelectric and/or
electrostrictive behaviour. However, semi-crystalline ferroelectric polymers such as the
copolymer of vinylidene fluoride and trifluorethylene (P(VDF-TrFE)) show some unexpected
characteristics, with ferroelectric behaviour above the Curie transition, but without piezoelectric
nor electrostrictive response1,2. Here, we demonstrate that electromechanical response of
ferroelectric crystalline domains does exist above the Curie transition and explain why it is not
observed in macroscopic measurements. To resolve these seemingly contradictory observations,
we have performed high-resolution nanomechanical measurements on P(VDF-TrFE) films and
in situ X-ray diffraction measurements on P(VDF-TrFE) capacitors (see Fig. 1), in both, the
ferro- and paraelectric states. We demonstrate that the particular semi-crystalline microstructure
in the paraelectric state, formed of ferroelectric crystalline domains embedded into a softer
amorphous phase, lead to the local electromechanical response to be counterbalanced by the
amorphous phase, effectively masking its macroscopic effect3.