Effects of Fe 3d–O 2p and Bi 6sp–O 2p orbital hybridizations in Nd doped BiFeO₃ ceramics

This study highlights the importance of electronic hybridizations in the FeO₆ octahedral distortion, structural evolution, magnetization, oxidation state and atomic bonding covalency in multiferroic (Bi_1−xNd_x)FeO₃ (x = 0–0.10) ceramics as the system approaches the morphotropic phase boundary (MPB). The Rietveld-refinement analysis reveals reductions of bismuth deficiency, oxygen vacancies, and nonpolar Bi₂Fe₄O₉ phase as Nd increases. The piezoresponse domain switching reveals a coexistence of polar ferroelectric rhombohedral and minor orthorhombic (nonpolar) phases. The piezoresponse ferroelectric polarization hysteresis loops are attributed to the reduced leaky conductivity in the Nd-doped compositions. The Fe K- and L_2,3-edges synchrotron X-ray absorptions suggest a mixture of Fe³⁺ and Fe⁴⁺ valence states and reduction of the FeO₆ octahedral distortion by the A-site Nd substitution. The oxygen K-edge synchrotron X-ray absorptions reveal that the hybridizations of the O 2p–Fe 3d and the O 2p–Bi 6sp orbitals were decreased with increasing Nd content.