Enhanced ferromagnetic and electric properties of multiferroic BiFeO₃ by doping with Ca

We report the dependence of magnetic and electric properties with the substitution of Bi³⁺ by Ca²⁺ into the crystal structure of multiferroic calcium doped BiFeO₃ for obtaining Bi_1-xCa_xFeO₃, 0 ≤ x ≤ 0.10 Stoichiometric mixtures of Bi₂O₃, Fe₂O₃ and CaO were mixed and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling. The obtained powder was pressed at 900 MPa to obtain cylindrical pellets and sintered at 800 °C for 2 h. X-ray diffraction and Rietveld refinement were used to evaluate the effect of Ca²⁺ on the crystal structure and to determinate the phase transition from rhombohedral α-BiFeO₃ (R3c) to orthorhombic β-BiFeO₃ (Pbnm). In addition, vibrating sample magnetometry (VSM) was used to have knowledge of magnetic order: antiferromagnetism and ferromagnetism were identified for α-BiFeO₃ and β-BiFeO₃, respectively. Dielectric tests determinate Debye-type relaxation for samples with the rhombohedral crystal structure and no Debye type relaxations for orthorhombic samples. Differences in AC conductivity of rhombohedral samples show different mechanism compared with the conductivity of orthorhombic samples. Ferromagnetic and electrical properties of synthesized materials show a strong correlation with the lattice distortions induced by the ionic ratio between Ca²⁺ and Bi³⁺. The effect of Ca²⁺ over leakage current has an interesting response, an increase of Ca²⁺ reduce one magnitude order the leakage current for α-BiFeO₃ samples; though for β-BiFeO₃ samples increase of Ca²⁺ raise the leakage current in one magnitude order.