Micro‐to‐nano domain structure and orbital hybridization in rare‐earth‐doped BiFeO3 across morphotropic phase boundary

This work demonstrates the critical role of orbital hybridizations in the FeO6 octahedral distortion, composition-driven phase transition, and bonding covalency in multiferroic (Bi1−xSmx)FeO3 (x = 0.10-0.20) ceramics in the vicinity of the morphotropic phase boundary (MPB). Sequential composition-driven transitions from the polar rhombohedral R3c to antipolar orthorhombic Pbam and then Pnma phases were revealed as the system crosses the MPB with increasing Sm. A coexistence of ferroelectric (FE) rhombohedral R3c and antiferroelectric (AFE) PbZrO3-like orthorhombic Pbam symmetries was identified by the 1/2{000}, 1/4{100}, 1/4{110}, 1/4{111}, and 1/4{121} superlattice diffractions at x = 0.12-0.16. In addition to R3c and Pbam space groups, the nonpolar SmFeO3-like orthorhombic Pnma space group becomes the predominant phase at x = 0.20 confirmed by the 1/2{100} superlattice diffractions. The Fe L3-edge and oxygen K-edge synchrotron X-ray absorptions indicate that the O 2p–Fe 3d and O 2p–Bi 6s/6p orbital hybridizations were decreased as the system approaches the MPB.