Enhanced dielectric and optical properties of nanoscale barium hexaferrites for optoelectronics and high frequency application

M-type barium hexaferrites with chemical composition Ba_1-xDy_xFe_12-yCr_yO₁₉ (x=0.0, 0.1, 0.2, and y=0.0, 0.4, 0.5) were synthesized via sol-gel auto-combustion method. The samples were pre-sintered at 400℃ for 3 h and sintered at 950℃ for 5 h. The changes in the structural, dielectric, and optical properties were studied after the substitution of Dy³⁺ and Cr³⁺ ions. X-ray diffraction (XRD) analysis confirms the formation of single phase hexaferrites with the absence of secondary phase. FTIR analysis gives an idea of the formation of hexaferrites with the appearance of two peaks at 438 cm^-1 and 589 cm^-1. The field emission scanning electron micrographs (FESEM) show a combination of crystallites with large shapes close to hexagonal platelet-like shape and others with rice or rod-like shapes, whereas EDX and elemental analysis confirm the stoichiometry of prepared samples. The calculated band gap from UV-vis NIR spectroscopy spectra was found to decreases with increase in Dy³⁺-Cr³⁺ substitution. The dielectric properties were explained on the basis of Maxwell-Wagner model. Enhancement of dielectric constant at higher frequencies was observed in all the samples. Low dielectric loss is also observed in all the samples and Cole-Cole plot shows that grain boundary resistance (R_gb) contribute most to the dielectric properties. The prepared samples exhibit properties that could be useful for optoelectronics and high frequency application.