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In situ observations of the domain evolution and the polarization rotation under bipolar cyclic and static electric fields are carried out for ͓001͔-oriented 68Pb͑Mg 1/3 Nb 2/3 ͒O 3 -32PbTiO 3 ͑PMN-32PT͒ single crystal which is located at the morphotropic phase boundary ͑MPB͒. The results demonstrate that after being poled in ͓001͔ direction, the original rhombohedral ͑R͒ phase is transformed into a monoclinic M C phase with Pm space group. When the single crystal is subjected to bipolar cyclic electric field, distinct domain-boundary structures are revealed which are unlikely to be detected in static electric loadings. The existence of R phase is also detected during the polarization reversal. Under static electric field, polarization rotation from M C to R occurs and, as the field increases, phase transition from M C to tetragonal ͑T͒ phase takes place. In the vicinity of regions where M C -T phase transition takes place, polarization reversal of M C phase is observed, which is attributed to the local stress field from the strain compatibility between the transitioned area and the nontransitioned area. With the removal of the field, T and M C phases retain while R phase reverses to M C phase. The results demonstrate that the energy differences among M C , R, and T phases are rather slim. Accordingly, the multiphase coexistence and polarization rotation under both cyclic and static electric loadings might be responsible for the ultrahigh piezoelectric response of the ͓001͔-oriented rhombohedral Pb͑Mg 1/3 Nb 2/3 ͒O 3 -PbTiO 3 single crystals near the MPB.

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We report an intriguing phenomenon of polarization enhancement for poly(vinylidene fluoride-trifluoroethylene) 75∕25mol% copolymer films under cyclic electric field. If the copolymer film is initially subjected to electric cycling at a comparatively low field magnitude, the remanent polarization (Pr) increases with the field cycles during the subsequent electric cycling at a higher field magnitude. The morphology and microstructure change during the electric cycling are examined. It is suggested that polymer chains in the interfacial layers between the crystalline and amorphous regions gradually increase in the ordering degree and that contributes to the polarization enhancement during electric cycling.