IMF2017

The field-induced polarization and electromechanical strain near the morphotropic phase boundary (MPB) are critical phenomena in ferroelectrics. However, the phase evolution, domain, and electronic state in multiferroics still lack consistent understanding near the MPB. We report phase revolution, domain structure, magnetization, ferroelectric polarization, strain, magnetization, phonon vibration, oxidation, and electronic hybridization in multiferroic (Bi_1-xRE_x)FeO₃ ceramics (RE=Nd and Sm) across the MPB. The Rietveld refinements reveal reductions of bismuth and oxygen vacancies with increasing rare earth. The local ferroelectric polarization and electromechanical strain hysteresis loops were observed by the piezoresponse force microscope (PFM) due to the reduced leaky conductivity. The Fe K- and L_2,3-edges synchrotron X-ray absorptions suggest a mixture of Fe³⁺ and Fe⁴⁺ valences and reduction of the FeO₆ octahedral distortion by the Nd substitution. The Fe L edge does not indicate valence shift by the Sm substitution. A sequential composition-driven transition from the ferroelectric rhombohedral R3c to nonpolar orthorhombic Pbam and then orthorhombic Pnma phases were revealed in (Bi_1-xSm_x)FeO₃ near the MPB. A coexistence of rhombohedral R3c and PbZrO₃-like orthorhombic Pbam symmetries was identified by the 1/2(ooo) and 1/4(ooo) superlattice diffractions for x=0.10-0.16. This study highlights the importance of the O 2p–Fe 3d and the O 2p–Bi 6sp orbital hybridizations, which play critical roles in the FeO₆ octahedral distortion and phase evolution.