Relaxor Ferroelectric Behavior from Strong Physical Pinning in a Poly(vinylidene fluoride-\textit{co}-trifluoroethylene-\textit{co}-chlorotrifluoroethylene) Random Terpolymer*

Although narrow single hysteresis loop (SHL) is observed for electron beam (e-beam) irradiated poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] random copolymers owing to strong chemical pinning in isomorphic (or defect-modified) crystals, it has not been achieved for P(VDF-TrFE)-based random terpolymers, such as P(VDF-TrFE-CFE) (CFE is 1,1-chlorofluoroethylene), which only exhibits double hysteresis loops (DHLs). This is attributed to the weak physical pinning of CFE units in isomorphic crystals. In this work, the comonomer CFE in the terpolymer was replaced by the larger chlorotrifluoroethylene (CTFE). Intriguingly, narrow SHLs were exclusively observed for the P(VDF-TrFE-CTFE) terpolymer above room temperature. This was attributed to the stronger physical pinning force of the larger CTFE, which has a smaller dipole moment (only 0.64 Debye). This result provides us further insight into the structure and behavior of relaxor ferroelectric polymers, which can help to design and develop new ferroelectric polymers with more desirable properties and enhanced performance.