Four Yuan Timnznfe Mnzn Power Ferrite Materials Research

With the rapid development of complete appliance to multifunction, miniaturation, lighter weight and integration, switching power supply applied in integrated electronics system is required for better performance. It requires that MnZn ferrites keep high initial magnetic permeability, low core loss, and high stability. Therefore, the study of wide working temperature and low loss MnZn power ferrite materials becomes the research focuses in domestic and foreign research.In this dissertation, TiMnZn power ferrites were prepared by conventional oxide ceramic process. The influences of main compositions, additives and processing on the microstructure and electromagnetic properties of MnZn ferrite were investigated. The results indicated that: Substituting with high valency Ti4+ ions can accommodate magnetocrystalline anisotropy constant(K1), magnetostriction coefficient,furtuer make the grains grow homogeneous and density,increase the initial permeability, decrease the hysteresis loss. Moreover Ti Substituted MnZn Ferrites owns high resistances of grain-boundary and grain, so it keeps low core loss. With the increase of Co2O3 from 0 wt% to 0.25wt%, There is no obvious change in the microstructure of Co2O3, but owing to the positive magnetocrystalline anisotropy of Co2+ ions, that could compensate to the negative value of K1 of ferrites, the initial permeability of MnZn ferrites increases, theμi～T and Pcv～T curve become flat. Adding appropriate SnO2(≤0.15wt%)in ferrites can accelerate the grain growth, improve the material density and the initial permeability, reduce coercive force. At the same, because SnO2 can increase the resistivity, ferrites posses the lowest power losses. With the increase of ZrO2 addition, the average grain size of MnZn ferrite increases monotonously, the initial permeability and saturation magnetic induction increase initially and then decrease, while the total losses (Pcv) decreases first and increases subsequently. Adding SnO2 or ZrO2 dopants to MnZn ferrites improves magnetic properties and core losses characteristics of the materials. SnO2 (0.15wt%) and ZrO2(0.015wt%) co-doping could make grain growth more homogeneous and dense. After ferrites being co-doped with SnO2 and ZrO2, density, permeability and electrical resistivity increase, and core losses decreases. With the increase of holding time, the grain size grows, the initial permeability increases, but if the holding time is too long, the volatile Zn increases, consequently the performance of the sintered samples degrades. The low oxygen partial pressure(2vol%)during sintering can improve microstructure and magnetic properties of the power ferrite, but the Fe2+ increases, so that power losses increases. Cooling rate significantly affects the microstructure and magnetic properties of the power ferrites. With the increase of cooling rate from 80oC/h to 200oC/h, the average grain size and the initial permeability of sintered samples gradually increase, but the power losses first decreases and then increases.