Large piezoelectric response of BiFeO3/BaTiO3 polycrystalline films induced by the low-symmetry phase

BaTiO3, BiFeO3 and BiFeO3/BaTiO3 polycrystalline films were prepared by the radio frequency magnetron sputtering on the Pt/Ti/SiO2/Si substrate. The phase structure, converse piezoelectric coefficient and domain structure of BaTiO3, BiFeO3 and BiFeO3/BaTiO3 thin films are characterized by XRD and PFM, respectively. The converse piezoelectric coefficient d(33) of BiFeO3/BaTiO3 thin films is 119.5 pm V-1, which is comparable to that of lead-based piezoelectric films. The large piezoelectric response of BiFeO3/BaTiO3 thin films is ascribed to the low-symmetry T-like phase BiFeO3, because the spontaneous polarization vector of T-like phase (with monoclinic symmetry) BiFeO3 can rotate easily under external field. In addition, the reduced leakage current and major domains with upward polarization are also attributed to the large piezoelectricity.