Origins of Ultrahigh Electromechanical Response in a New Class of Relaxor Ferroelectric Polymers

Due to their high pliability, easy fabrication into complicated shapes and large areas, light weight, and low cost, ferroelectric polymers are attractive for a broad range of electromechanical (EM) applications. On the other hand, the low EM properties of polymers, compared with inorganic counterparts, limit device performance. Recently, we reported a new class of relaxor ferroelectric polymers, poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-fluorinated alkyne) (PVDF-TrFE-CFE-FA) tetrapolymer (Science, 2022, 375, 1418) that, at FA content near 2 mol%, generates giant electrostriction at ultralow electric fields. Moreover, the tetrapolymer exhibits electromechanical coupling factor and piezoelectric fields at low DC bias much higher than those of PZT ceramics, the most widely used piezoelectrics. Here, we study the phase transition behavior of the tetrapolymer as a function of FA content. Increasing FA content weakens the relaxor behavior, and at high FA content (4 mol% FA), the tetrapolymers exhibit normal ferroelectric response. A diffused critical endpoint transition region at compositions near 2 mol% FA is observed, at which the energy barriers between the weak relaxor and polar phase almost vanish; thus, a small electric field can induce a large EM response.