Structural, spectroscopic, magnetic and electrical characterisation of polycrystalline Bi1-xCaxFeO3-x/2 (x!0.1)

The crystal structure and physical properties of multiferroic polycrystalline Ca2+-doped BiFeO3 samples have been investigated. The present experimental investigation suggests that Bi1-xCaxFeO3-x/2 (x! 0.1) can be considered as a solid solution between BiFeO3 and CaFeO2.5. 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 BiFeO3. All compositions studied show antiferromagnetic behaviour along with a ferromagnetic component that increases with Ca2+ doping. The resistivities of the Bi1-xCaxFeO3-x/2 samples at room temperature are of the order of 109 "cm and decrease with increasing Ca2+ content. Arrhenius plots of the resistivity show two distinct linear regions with activation energies in the range of 0.4-0.7 and 0.03-0.16 eV. 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 maximu