PFM images after polarization: (a) P(VDF-TrFE); (b) P(VDF-TrFE) + 20%BPZT + Fe; (c) P(VDF-TrFE) + 5% BaTiO3; (d) P(VDF-TrFE) + 0.5%DTGS; (e) P(VDF-TrFE) + 10%DTGS; (f) PZT