Structural, optical, dielectric and magneto-dielectric properties of Ca2+-modified BiFeO3 multiferroics

We report the synthesis and characterization of low leakage and large magneto-dielectric (MD) sol-gel derived Bi1-xCaxFeO3 (x = 0, 5%, 10%) [BCFO] nanocrystalline multiferroic ceramics. The X-ray diffraction (XRD) data analysis revealed a rhombohedral structure for pure BiFeO3 (BFO) and 5% Ca-doped BFO, as well as a mixture of rhombohedral and orthorhombic (R3c + Pbnm) structures for 10% Ca-doped BFO. The dielectric permittivity (epsilon) data exhibit anomalous dielectric behavior near the magnetic phase transition temperature of BFO, supporting the presence of the MD effect at room temperature. At room temperature, 10% Ca-doped BFO exhibits a strong magneto-dielectric coupling (MD) and shows positive MD effects. The frequency-dependent ac conductivity follows modified Jonscher's power law. Incorporating Ca reduces the leakage current by five orders of magnitude (for x = 10%) and significantly improves the MD coupling. The optical band gap also significantly reduced from 2.24 to 1.70 eV after calcium substitution, which makes it suitable for use in photovoltaic applications.