The effect of defects introduced by high-energy electron irradiation on microstructure and properties in poly(vinylidene fluoride- trifluoroethylene) [P(VDF-TrFE)] is reported. In studies of the copolymers, it is found that as defect concentration increases, the material can be changed from a normal ferroelectrics to a relaxor ferroelectrics (RFE) and then to a simple relaxor. Correspondingly, the crystalline morphology changes from a coexistence of polar and non-polar phases to a macroscopically uniform non- polar phase, as revealed by x -ray data. It was observed that the dielectric property in the copolymers with a different amount of defects was well described by the Vogel-Fulcher (V-F) relationship. Based on the experimental data, a critical size, which is the smallest size of crystal with ferroelectric phase, of about 5 nm was obtained for the copolymer. The RFE developed here exhibits a massive electrostrictive strain which is very attractive for many actuator and transducer applications and a high dielectric constant which is attractive for development of high- density energy storage capacitors and electronic packaging.