Tailoring 0.8BiFeO₃ -0.2CaTiO₃ nanocomposite properties via (Dy, Hf) co-doping: a comprehensive study of structural, dielectric, magneto-dielectric and optical characteristics

Sol-gel synthesis method was employed to fabricate nanocomposites of (Dy, Hf) co-doped 0.8BiFeO₃ -0.2CaTiO₃ (Bi_0.75Dy_0.05Fe_0.80O₃-Ca_0.20Ti_0.18Hf_0.02O₃/BDyFO-CTHfO composite). Structural analysis, utilizing X-ray diffraction and Rietveld refinement with Fullprof software, confirmed a rhombohedral structure with space group R3c and an orthorhombic structure with Pnma space group. Particle size determined through Scherrer's formula was ∼15 nm. FESEM studies revealed irregular and slightly dense inhomogeneous grains. Dielectric permittivity (e) and tangent loss (tan d) were investigated as functions of frequency from 100 Hz to 1 MHz at different temperatures ranging from 303 to 663 K. The dielectric dispersion behaviour was attributed to Maxwell-Wagner-type polarization, with a notable anomaly in dielectric permittivity observed near the magnetic phase transition temperature (TN ∼643 K) of BiFeO₃. Frequency-dependent ac conductivity exhibited low-frequency dispersion following Jonscher's power law. Presence of ferroelectricity was confirmed by the polarization-electric field (PE) loop. Magneto-dielectric characteristics were assessed in a frequency range of 100 Hz-1 MHz under a magnetic field of 0-2 Tesla. Impedance spectroscopy highlighted electrical properties, distinguishing grain and grain boundary contributions via Nyquist plot with respect to the magnetic field. The BDyFO-CTHfO composite demonstrated significant absorption and ∼ 25% transmittance in the visible spectrum. The material exhibited a band gap (E_g) of 1.97 eV, suggesting potential applications in ultrafast optoelectronic devices. (author)