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 (ε) and tangent loss (tan δ) 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 (T_N ~ 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.