Phase transition regulation and concurrent ferroelectric and magnetic improvement in BiFeO3 via rare-earth multi-substitution strategy

To investigate the synergistic effects of multi-element rare-earth doping in BiFeO 3 ceramics, this study prepared a series of co-doped samples. A comparative analysis was conducted, focusing on the differences in crystal structure, microstructure, and multiferroic properties between the co-doped samples and their singly-doped counterparts. Structural analysis confirms that the concentration and ionic radius of the rare-earth dopants are critical factors inducing the transition of the primary phase from rhombohedral R 3 c to orthorhombic Pna 2 1 , a process often accompanied by multi-phase coexistence. Specifically, a smaller rare-earth ionic radius (Sm-doped BiFeO 3 ) leads to a superior magnetic properties, where remanent magnetization M r  = 74.5 emu/mol, but poorer ferroelectric performance, with the remanent polarization P r  = 4.41 μC/cm 2 . In contrast, a larger ionic radius (La-doped BiFeO 3 ) enhances the ferroelectric properties ( P r  = 38.08 μC/cm 2 ), although the magnetic performance remains suboptimal ( M r  = 20.45 emu/mol). Specifically, the multi-doped Bi 0.82 (La 1/3 Nd 1/3 Sm 1/3 ) 0.18 FeO 3 (LNS018) ceramic achieved a remarkable remanent polarization ( P r ) of 40.90 μC/cm 2 under 170 kV/cm, which is superior to its single-doped counterparts. Concurrently, its remanent magnetization ( M r ) reached 39.8 emu/mol. This superior performance is attributed to the construction of a morphotropic phase boundary between the R 3 c and Pna 2 1 phases, which was effectively tailored by the multi-substitution strategy. Compared to single rare-earth substitution, co-doping induces greater lattice distortion and more refined domain structures, contributing to the enhanced multiferroic performance.