Micro‐to‐nano domain structure and orbital hybridization in rare‐earth‐doped BiFeO 3 across morphotropic phase boundary

This work demonstrates the critical role of orbital hybridizations in the FeO 6 octahedral distortion, composition‐driven phase transition, and bonding covalency in multiferroic (Bi 1− x Sm x )FeO 3 ( x = 0.10‐0.20) ceramics in the vicinity of the morphotropic phase boundary (MPB). Sequential composition‐driven transitions from the polar rhombohedral R 3 c 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 R 3 c and antiferroelectric (AFE) PbZrO 3 ‐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 R 3 c and Pbam space groups, the nonpolar SmFeO 3 ‐like orthorhombic Pnma space group becomes the predominant phase at x = 0.20 confirmed by the 1/2{100} superlattice diffractions. The Fe L 3 ‐edge and oxygen K‐edge synchrotron X‐ray absorptions indicate that the O 2 p –Fe 3 d and O 2 p –Bi 6 s /6 p orbital hybridizations were decreased as the system approaches the MPB.