A study on the electrical and dielectric properties of SrGd_xFe_12−xO₁₉ (x = 0.00–0.05) nanosized M-type hexagonal ferrites

Single-phase SrGd_xFe_12−xO₁₉ (x = 0.00–0.05) nanosized M-type hexagonal ferrites (NHFs) were prepared via citrate sol–gel route. The formation of Gd substituted Sr-hexaferrites has been confirmed by XRD, SEM, TEM and EDX for all substitutions. The X-ray powder patterns revealed the hexagonal crystal structure of all products. The electrical and dielectric properties of SrGd_xFe_12−xO₁₉ NHFs were investigated extensively with an impedance spectroscopy up to 3.0 MHz from 20 to 120 °C. Both electrical and dielectric components including ac/dc conductivity, dielectric constant, dielectric loss and lossy tangent were evaluated for measurement temperatures up to 120 °C. It has been indicated that ac conductivity generally complies with power law rules, mainly dependent on Gd³⁺-ion substitution ratios. The impedance analysis showed that due to the influence of various Gd³⁺-ion substitution ratios in the NHFs, the conduction mechanisms can mainly be attributed to the grain-grain boundaries. The dielectric constant of SrGd_xFe_12−xO₁₉ NHFs owns a normal dielectric distribution with the frequency, largely due to varying substitution ratios. In other words, the variation of Gd³⁺-ion substitution can be used to modify the conduction mechanism of NHFs. Therefore, the observed change in dielectric properties as a function of frequency can be clarified on a phenomenological basis by Koop’s model of the electrical conduction mechanism in most composite ferrites.