Alterung und Ermüdung von Ferroelektreten: experimentelle und theoretische Untersuchungen

• Antragstellerinnen / Antragsteller: Professor Dr.-Ing. Heinz von Seggern; Professorin Dr.-Ing. Bai-Xiang Xu
• Fachliche Zuordnung: Polymermaterialien ; Herstellung und Eigenschaften von Funktionsmaterialien ; Mechanische Eigenschaften von metallischen Werkstoffen und ihre mikrostrukturellen Ursachen
• Förderung: Förderung von 2016 bis 2018
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 299327252

• Erstellungsjahr: 2018

Zusammenfassung der Projektergebnisse

For fluoropolymer arrays with tubular air channels the quasi-static piezoelectric 𝑑33 coefficient was theoretically derived and its upper limits were evaluated considering charging and mechanical properties of the arrays. In order to optimize the 𝑑33 coefficient the remanent polarization and the mechanical properties were taken into account, both being strongly dependent on the air channel geometry as well as on the wall thickness of the FEP tubes. The model predictions are compared with experimental d33 coefficients for two particular arrays with equal air gaps of 250 μm, but with different wall thickness of utilized FEP tubes of 50 μm and 120 μm, respectively. The arrays made of FEP tubes with the wall thickness of 25 μm were also manufactured and investigated. The latter arrays exhibit a superb piezoelectric response of up to 500 pC/N which is comparable to PZT ceramics. In addition, the issues related to temporal stability and fatigue resistance at prolonged dynamic mechanical load at different pressures and frequencies were experimentally investigated. The electromechanical properties of the ferroelectrets can become instable through different mechanisms. One is the viscoelastic effect of the bulk material and the ferroelectret structure. In particular, due to the viscoelastic flow, both the material and the structure can relax and leads practically to change in the dipoles and thus the d 33 coefficient. Moreover, the dynamic mechanical loading has been found to have considerable influence on stability of the electromechanical properties. The influence of frequency and applied stress magnitude both can play a role, especially when the thickness of the FEP layer is low, e.g. 25 μm or lower. Finally, for the tubular ferroelectrets, the structure instability of the thin wall, i.e. the inward bowing, during processing, charging and function, can also impact the electromechanical property.

Projektbezogene Publikationen (Auswahl)

• “Dynamic pull-in instability of a prestretched viscous dielectric elastomer under electric loading,” Acta Mech 2017, 228, 4293–4307
  D. Eder-Goy, Y. Zhao and B.-X. Xu
  
• “Effect of degree of crystallographic texture on ferro- and piezoelectric properties of Ba0.85Ca0.15TiO3 piezoceramics,” J Am Ceram Soc. 2017;100, 2098–2107
  J. Schultheiß, O. Clemens, S. Zhukov, H. von Seggern, W. Sakamoto and J. Koruza
  
• “Polarization-switching dynamics in bulk ferroelectrics with isometric and oriented anisometric pores,” J. Phys. D: Appl. Phys. 2017, 50, 045303
  R. Khachaturyan, S. Zhukov, J. Schultheiß, C. Galassi, C. Reimuth, J. Koruza, H von Seggern and Y. Genenko
  
• “Analytical prediction of the piezoelectric d33 response of fluoropolymer arrays with tubular air channels,” Scientific reports, 2018, 8, 4597
  S. Zhukov, D. Eder-Goy, S. Fedosov, B.-X. Xu and H. von Seggern
  
• “Tubular fluoropolymer arrays with high piezoelectric response,” J. Phys. D: Appl. Phys. 2018, 27, 0150102016
  S. Zhukov, D. Eder-Goy, C. Biethan, S. Fedosov, B.-X. Xu and H. von Seggern