The discovery of a universal behavior in rare‐earth (RE)‐substituted perovskite BiFeO3 is reported. The structural transition from the ferroelectric rhombohedral phase to an orthorhombic phase exhibiting a double‐polarization hysteresis loop and substantially enhanced electromechanical properties is found to occur independent of the RE dopant species. The structural transition can be universally achieved by controlling the average ionic radius of the A‐site cation. Using calculations based on first principles, the energy landscape of BiFeO3 is explored, and it is proposed that the origin of the double hysteresis loop and the concomitant enhancement in the piezoelectric coefficient is an electric‐field‐induced transformation from a paraelectric orthorhombic phase to the polar rhombohedral phase.

We report on the discovery of a lead-free morphotropic phase boundary in Sm doped BiFeO 3 with a simple perovskite structure using the combinatorial thin film strategy. The boundary is a rhombohedral to pseudo-orthorhombic structural transition which exhibits a ferroelectric (FE) to antiferroelectric (AFE) transition at approximately Bi 0.86 Sm 0.14 FeO 3 with dielectric constant and out-of-plane piezoelectric coefficient comparable to those of epitaxial (001) oriented Pb(Zr,Ti)O 3 (PZT) thin films at the MPB. The discovered composition may be a strong candidate of a Pb-free piezoelectric replacement of PZT.

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We report on the controlled multiphase thin film growth in the Bi-Fe-O system. By varying the deposition oxygen pressure, the dominant phase formed in the film continuously changes from ferroelectric BiFeO 3 to a mixture of ␣-Fe 2 O 3 and ferromagnetic ␥-Fe 2 O 3. X-ray diffraction and high-resolution transmission electron microscopy have revealed that epitaxial multiferroic nanocomposites consisting of BiFeO 3 and Fe 2 O 3 are formed when the deposition pressure is Ϸ5 mTorr. In order to investigate the previously reported anomalous enhancement in magnetization in BiFeO 3 , we have fabricated a thickness gradient pure BiFeO 3 film. The out-of-plane lattice constant was found to increase continuously as the thickness is decreased from 300 to 5 nm, but no significant enhancement in magnetization was observed.