Influence of Gd³⁺ substitution and preparation technique on the optical and dielectric properties of Y₃Fe₅O₁₂ garnet synthesized by standard ceramic and coprecipitation methods

Micro-size and nano-size samples of (Gd_xY_3−xFe₅O₁₂; x = 0, 0.25, 0.5, 0.75, and 1) garnet ferrites were prepared by the standard ceramic method (CER) and the coprecipitation (COP) method. The influences of Gd³⁺ doping and preparation methods on the optical and dielectric properties were compared for these micro-size and nano-size compositions for the first time. X-ray diffraction data confirmed the formation of a single phase of the garnet cubic structure for all samples. It was found that there is a good agreement between the theoretical and experimental lattice parameter estimated values. The Fourier transform infrared spectroscopy was used to study the cation distributions among the different crystallographic sites. Moreover, values of energy gap (E_g) for the investigated samples were determined from the diffused reflectance spectroscopy measurements. These values were found to be higher for (COP) samples than for (CER) ones and slightly increased by increasing Gd³⁺ content in both series prepared via the two techniques. Furthermore, resistivity (ρ_ac), dielectric constant (ε′), and dielectric loss (ε″) showed a decrease with increasing frequency (f) for all samples. For the samples prepared by (CER) method, ρ_ac increases with increasing Gd³⁺ content while for the samples prepared by (COP) method, ρ_ac increases for 0 ≤ x ≤ 1 except for the sample x = 0.5. Values of ρ_ac for samples prepared by (COP) method are higher than those prepared by (CER) method. Both ε′ and ε″ had the reverse behavior of ρ_ac. Obtained results were explained according to different models.