Effect of La/Cr codoping on structural transformation, leakage, dielectric and magnetic properties of BiFeO₃ ceramics

BiFeO₃ (BFO) and Bi_1−x La _x Fe_0.9Cr_0.1O₃ (x = 0.1–0.2, BLFC _x=0.1–0.2) ceramics were prepared by modified solid-state reaction. The influence of La/Cr codoping on the microstructure, leakage, dielectric and magnetic properties of BFO was studied. It is found that the La/Cr codoping can induce a structural transformation from a rhombohedral (R3c) phase to a triclinic (P1) phase, suppress the formation of oxygen vacancies and modulate the spiral spin structure. With the increasing La concentration, the leakage current density can be diminished by over two orders of magnitude compared with undoped BFO, in a reasonable range for device applications. The dielectric loss follows almost the same trend as the leakage current, while the dielectric constant is raised to 400.8 at 100 kHz for x = 0.2, over eight times larger than that of undoped BFO. The substantially enhanced magnetization can be mainly attributed to the suppression of the spiral spin structure and a new ferromagnetic Fe³⁺–O²⁻–Cr³⁺ super-exchange interaction. More interestingly, abrupt changes are observed around x = 0.15, not only in microstructure but also in electrical and magnetic properties, which may indirectly reflect the coupling effect among them. The BLFC _x=0.2 ceramic shows the highest magnetization and dielectric constant together with the lowest leakage current and dielectric loss. The results indicate that the La/Cr codoping can effectively improve the magnetic and electrical properties of BFO ceramic for potential applications in magnetoelectric devices.