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BiFeO3 (BFO) and Bi1−x La x Fe0.9Cr0.1O3 (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.

Cu(Cr0.96−xMg0.04Mnx)O2−δ ceramics (0 ≤ x ≤ 15 at.%) were prepared by solid-state reaction. The influence of Mg acceptor codoping on microstructure, magnetic, and optical properties was studied. The codoping with Mg acceptors and the resulting lattice expansion are both favorable for the enhancement of hole density. Furthermore, the lower valence of Mg2+ compared with Cr3+ enables the mixed valence state of Mn ions: Mn3+ and Mn4+, and hence induces the hole-mediated double-exchange mechanism not only between Mn3+ and Cr3+ but also between Mn3+ and Mn4+. The coexistence of two ferromagnetic interactions and the high hole density are responsible for the improved saturation magnetization and Curie temperature. For photoluminescence, an unusual near-infrared emission at 1.5 eV is observed in the Mn-contained samples and can be attributed to the internal transition between the e and t2 states of the Mn3+ impurity band. The emission intensity is primarily affected by two factors: the Mn3+ concentration and the position of the Fermi level. The results show that codoping with Mg acceptors is an effective way to strengthen the hole-mediated ferromagnetic interactions in CuCrO2 delafossite.