Microwave behavior of substituted lithium ferrite composites in X-band

Dense and crack-free substituted lithium ferrite-polymer composite films of thickness ∼80 μm were fabricated. The substituted lithium ferrite powders with general composition Li0.5−x/2CoxMn0.1Fe2.4−x/2O4, where x=0.0, 0.2, 0.4 and 0.6, were prepared by citrate-route. Epoxy resin EPG-280 was used as a polymer. The composite films required lower processing temperature ∼100 °C. Cavity-perturbation technique was employed to measure the complex permittivity (∈′-j∈″), and the complex permeability (μ′−j μ″), of the composite films at X-band microwave frequencies (8-12 GHz). The dispersion in the complex permittivity of ferrite composite films was found to be significant. The maximum value of ∈″ was observed for the film with x=0.6 and 75% volume loading of ferrite component. The permeability μ′ of films was found to decrease with an increase in frequency as well as with the volume loading of ferrite component in composite films. The single-phase spinel structure of the substituted lithium ferrite powders for compositions x=0.0, 0.2, 0.4 and 0.6 was confirmed by X-ray diffraction pattern. The microstructure of composite films was observed by scanning electron microscopy.