The Preparation And Substitution Performance Study Of Li-Zn Ferrites Synthesized By Sol-gel Method

Lithium ferrite LiFe_2.5O₄ has drawn attention from a long time due to its unique excellent properties such as high saturation magnetization,low dielectric losses,excellent square shape of hysteresis curve,excellent dielectric properties,high Curie temperature?620 oC?,high chemical inertness,thermal stability,high resistivity,low eddy current losses,low cost and safety.Due to these desirable properties,it is widely used in prolonged technological applications such as lithium ion batteries,high-density magnetic recording,magnetic fluids,magneto-caloric refrigeration,magnetic resonance imaging enhancement,magnetically guided drug delivery and is very attractive as a substitute for expensive yttrium iron garnet?YIG?in mass-scale microwave devices such as circulators,phase shifters,isolators,power transformation in electronics,memory core,antennas and high-speed digital tapes.In this study,we used a variety of analytical grade metalic nitrate granules or solutions as the raw material and citric acid as a complexing agent,and prepared lithium zinc ferrite powders using the sol-gel method,and then sintered the pressed green bodies.With the technology of X-ray diffraction?XRD?,vibrating sample magnetometer?VSM?,LCR meter,scanning electron microscopy?SEM?,impedance analyzer,we investigated the microstructure?densification?magnetic and dielectric properties of samples.The following issues were discussed in detail.Sol-gel method was adopted to prepare series of Li_0.5Zn_xFe_2.5-xO₄?0.10?x?0.30?spinel ferrite samples.Test results showed that,the lattice constant of powder samples gradually increases with the increase of Zn content,the average grain size is decreased.The saturation magnetization of the sintered block and the initial magnetic permeability gradually increased with the substitution of Zn,and the coercive is decreased.The Curie temperature decreased because of the addition of the non-magnetic Zn²⁺ ion.Both of dielectric constant and loss?at high frequency?were reduced;Although the saturation magnetization of Li_0.5Zn_0.2Fe_2.3O₄ ferrite powder increased with the annealing temperature,the too high or too low annealing temperature would affect the activity of powders,leading to the low density and poor soft magnetic properties of sintered bulks.Besides,raising the sintering temperature would help improve Li-Zn ferrite density and saturation magnetization and reduce the coercive.But the initial permeability of samples increased with the temperature when the sintered temperature is too high?above 1000 oC?,which meant the temperature stability was deteriorated.Furthermore,using the sol-gel method,Li_0.5Zn_0.2Mg_xFe_2.3-xO₄?0?x?0.20?and Li_0.5Zn_0.2Mn_xFe_2.3-xO₄?0?x?0.20?ferrite samples were prepared respectively.Mg and Mn atoms entered into the crystal lattice of ferrite successfully as the substitution of Fe atoms and all samples were single ferrite phase.Both of Mg and Mn doping would decrease the density of bulk samples and the coercivity was increased.And the initial permeability,dielectric constant and dielectric loss also decreased.Curie temperature had different degrees of decrement.Mg-doping caused the grains size of sintered samples become uniform and the appropriate amount of Mn ions will increase the saturation magnetization of the ferrite samples.