Synthesis of Li-Zn ferrites doped with Mg2+ by the sol-gel combustion method and its microwave electromagnetic properties

Ferrite powders Li0.1Zn0.8Mgx Fe2.1-xO4(x = 0, 0.01, 0.03, 0.05, 0.07, mole fraction) were synthesized using the sol-gel combustion method. The formation process, structure, and surface morphology of samples were characterized using the thermogravimetric-differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and scanning electron microscope. The results show that ferrite powders with pure spinel phase are formed when x≤0.05. The lattice parameters of ferrites first increase and then decrease with substituted amounts. The FTIR spectrum shifts to a lower wave number, which is attributed to the doping of Mg2+. The microwave electromagnetic properties of the samples were studied using the network analyzer (Agilent 8722ET) at the frequency range from 2 GHz to 18 GHz. It is shown that small amounts of Mg2+ substitution can adjust microwave electromagnetic parameters. The dielectric dissipation (tan δ) exhibits two maximal peaks at the frequency of 7 GHz and 15 GHz, respectively, and the peak values of tan δ are about 0.1 and 0.49 when x = 0.05. It is indicated that the microwave electromagnetic loss properties are excellent when x = 0.05. The reasons behind these findings are discussed using electromagnetic theory.