Structural, spectroscopic, magnetic and electrical characterization of Ca-doped polycrystalline bismuth ferrite, Bi _1xCa _xFeO _3x/2 (x0.1)

The crystal structure and physical properties of multiferroic polycrystalline Ca ²⁺-doped BiFeO ₃ samples have been investigated. The present experimental investigation suggests that Bi _1xCa _xFeO _3x/2 (x0.1) can be considered as a solid solution between BiFeO ₃ and CaFeO _2.5. The oxidation state of Fe in these materials is +3 and charge balance occurs through the creation of oxygen vacancies. For each composition, two structural phase transitions are revealed as anomalies in the variable-temperature in situ x-ray diffraction data which is consistent with the well-established high-temperature structural transformation in pure BiFeO ₃. All compositions studied show antiferromagnetic behaviour along with a ferromagnetic component that increases with Ca ²⁺ doping. The resistivities of the Bi _1xCa _xFeO _3x/2 samples at room temperature are of the order of 10 ⁹cm and decrease with increasing Ca ²⁺ content. Arrhenius plots of the resistivity show two distinct linear regions with activation energies in the range of 0.40.7 and 0.030.16eV. A correlation has been established between the critical temperatures associated with the structural phase transitions and the multiferroic properties. A composition of x=0.085 is predicted to show maximum magneto-electric coupling.