The Low H_clizn Ferrite Dielectric Properties

LiZn ferrites are attractive for manufacturing latching phase shifters and other microwave applications because of their saturation magnetization with wide adjustable range, high Curie temperature, low stress sensitivity of remanence and low cost without expensive ingredients. As the key component of phased array antenna, phase shifter has strict standards on driving system and insertion loss, which are related with the coercivity, dielectric loss and temperature stability of microwave ferrite materials. For these sakes, LiZn ferrites with low coercivity were studied, by means of optimizing the compositions and preparing processes to reduce the coercivity and dielectric loss of the LiZn ferrites.First, the compositions and additive of the LiZn ferrites prepared by conventional ceramic process were investigated. The results indicate that the saturation magnetization and remanence increase first and decrease with increasing Mn-substituted content, whereas the coercivity has an opposite change. The dielectric loss tangent increases due to the decrease in DC resistivity with increasing Mn concentration, but the quantity class of dielectric loss tangent is still at 10-4. The optimum iron-deficient composition of LiZn ferrite enhances saturation magnetization and reduces coercivity, but has little effect on the remanence ratio. Meanwhile, optimum iron deficiency decreases the dielectric loss of LiZn ferrites. A certain amount of lithium-rich in LiZn ferrites composition increases the DC resistivity and improves the dielectric properties. However, a great quantity of lithium-rich results in serious deterioration on magnetic properties and other polycrystalline phases appearance. Ni substitution has little influence on the properties of LiZn ferrites, and the coercivity gets smaller with optimum Ni concentration. The LiZn ferrites doped with Bi2O3 were studied. The results show that Bi2O3 acts effective in promoting grain growth and solid state reaction, which improve the density, remanence, coercivity and saturation magnetization of LiZn ferrites. With the increase of Bi2O3, the DC resistivity increases which decreases the dielectric constant and dielectric loss tangent.In addition, the preparing processes of LiZn ferrites were studied. The results show that the coercivity increases first and decreases with increasing calcining temperature. As to the dielectric properties, the dielectric loss decreases first and increases with increasing calcining temperature. Optimum sintering parameters are beneficial to decrease the coercivity and minimize the unfavorable influences on the DC resistivity.