Enhanced Piezoelectricity in Poly(vinylidenefluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) Random Terpolymers with Mixed Ferroelectric Phases

Piezoelectric polymers are attractive as next-generation flexible, wearable, and implantable electronic materials forenergy, sensor, and medical applications. Here, we report the enhancement of the longitudinal piezoelectric coefficients (d33)ofpoly(vinylidenefluoride) (PVDF)-based ferroelectric polymers via the synthesis and characterization of poly(vinylidene difluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] terpolymers with coexisting mixed normal ferroelectric andrelaxor phases. Specifically, the terpolymer with a composition of VDF/TrFE/CTFE = 64.5/33.1/2.4 mol % exhibits ad33of-55.4pC/N, corresponding to an 85% increase compared with the well-known P(VDF-TrFE) 65/35 mol % copolymer. Themicrostructures, chain conformations, Curie transitions, and crystal structures of the terpolymers have been investigated as afunction of the CTFE content. The structural and conformational analyses show that the incorporation of CTFE into theferroelectric P(VDF-TrFE) facilitates the formation of the relaxor phase. The maximumd33is present in the terpolymers with theCTFE content ranging from 1.7 to 5.0 mol %. A further increase in the CTFE concentration renders the terpolymer a ferroelectricrelaxor without the polar ferroelectric phase. The phase transition induced by varying the CTFE content of the terpolymers isevidenced by the dielectric and electromechanical characterizations. This work demonstrates a new structural modification approach to improve the piezoelectricity of the ferroelectric polymers