Processing and properties of cobalt-substituted lithium ferrite in the GHz frequency range

*Polycrystalline cobalt- substituted lithium ferrites with general formula Li0.5-x/2CoxFe2.5-x/2O4 (x = 0.0, 0.2, 0.4 and 0.5) were prepared by a non-conventional citrate precursor method, which is advantageous over conventional (solid state sintering) method because of low temperature (600degreesC) processing. Small amounts of Bi2O3 (0.5 wt.%) were added to reduce the porosity and dielectric loss tangent at sintering temperatures (1000-1200degreesC). The complex magnetic permeability (mu' - jmu'') and complex dielectric permittivity (is an element of' - jis an element of) of cobalt-substituted lithium ferrites were measured in the 8-13 GHz microwave frequency range. The systematic variations of the real and imaginary parts of both permeability and permittivity with frequency and composition have been analyzed. The minimum value of is an element of' similar to 11.3 measured for x = 0.4 substituted lithium ferrite is observed for a sample sintered at 1000degreesC. The highest values of is an element of' and is an element of'' were observed for samples sintered at 1200degreesC mu' varies between 1.84 and 3.90 for pure and cobalt-substituted lithium ferrite bulk ceramics. The spinet structure of the samples was confirmed by X-ray diffraction (XRD). (C) 2004 Elsevier Ltd and Techna S.r.l. All rights reserved.