Modulation of electric and magnetic properties in 0.70BiFeO₃-0.30BaTi_0.9O₃ ceramics with controlled oxygen vacancies and Fe²⁺/Fe³⁺ ratio

The physical properties of transition-metal oxides are closely related to defect concentrations. Herein, the modulation of oxygen vacancies and Fe²⁺/Fe³⁺ ratio on the electric and magnetic properties in Ti non-stoichiometry 0.70BiFeO₃-0.30BaTi_0.9O₃ ceramics were investigated systematically. As the concentration of oxygen vacancies decreases, grain size increases and the perovskite unit cell with rhombohedral phase becomes more distorted. The maximum dielectric constant gradually increases and the relaxation factor decreases with decreasing oxygen vacancy concentration. The enhancement of ferroelectricity is consistent with the degree of the distortion of the perovskite lattice, and the reduction of internal bias field comes from the reduction of the defect dipoles in the ceramics. At low oxygen partial pressure, Fe²⁺ defects are preferred and form the double exchange interaction between Fe²⁺ and Fe³⁺ ions, which will enhance the magnetization.