【作者】 聂建华；

【导师】 何华辉；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2004， 博士

【摘要】 MnZn铁氧体材料是现代电子工业及信息产业的基础材料。随着通讯技术、计算机技术的飞速发展,对MnZn铁氧体材料提出了越来越高的要求。按应用特征MnZn铁氧体可以分为三大类型,即功率铁氧体、高磁导率铁氧体和抗电磁干扰铁氧体。目前,功率铁氧体正朝着高频率、低损耗方向发展,高磁导率铁氧体则朝着磁导率更高、频率稳定性更好的发展方向发展。本文将主要对具有优良性能的功率铁氧体和高磁导率铁氧体的制备技术和机理进行研究。本文首先从MnZn铁氧体的晶格结构分析出发,理论上解释了MnZn铁氧体磁性的来源;然后利用分子场理论,研究了MnZn铁氧体材料的分子磁矩、居里温度、饱和磁感应强度等电磁参数与MnZn铁氧体磁性能的关系;最后从磁畴理论出发,研究了MnZn铁氧体的损耗和磁导率的机理,提出了降低MnZn铁氧体损耗和提高磁导率的方法,为制备高性能MnZn铁氧体材料打下理论基础。本文还研究了MnZn铁氧体材料的制备工艺过程,指出了MnZn铁氧体制备工艺中应该注意的问题。首先对MnZn铁氧体的形成机理进行了分析,并对MnZn铁氧体形成的固相反应动力学进行了研究;然后分析了MnZn铁氧体在烧结过程中的物理化学变化,研究了烧结工艺对MnZn铁氧体磁性能的影响,提出了制定MnZn铁氧体烧结工艺的原则。对功率MnZn铁氧体而言,在分析了MnZn铁氧体磁滞损耗、涡流损耗和剩余损耗的基础上,指出制备高性能功率MnZn铁氧体材料的关键工艺在于掺杂和烧结工艺的控制,在此基础上,对制备高性能功率MnZn铁氧体材料的掺杂和烧结工艺进行了深入研究。首先,研究了各种杂质CaCO3、SiO2、TiO2、ZrO2、Ta2O5、Er2O3等杂质对功率铁氧体磁损耗的影响,并对杂质的作用机理进行了研究。研究结果发现加入适量的上述杂质均可以有效降低功率铁氧体材料的磁损耗,其原因在于杂质离子在铁氧体的晶界处大量聚集,在晶界形成了1-10um厚的高电阻率晶界绝缘层,提高了铁氧体的电阻率,从而降低铁氧体的磁损耗。其次,研究了SnO2杂质对铁氧体材料的磁性能的影响,并改进了铁氧体工艺,将加入SnO2杂质时间提前,并降低预烧温度,改进后的工艺可以进一步降低MnZn铁氧体的高频损耗。其原因在于部分的Sn4+离子<WP=5>部分取代Fe3+离子进入铁氧体晶格,提高了铁氧体晶粒内部的电阻率;另一部分的Sn4+离子与Ca2+、Si4+、Nb5+和V5+等离子一起形成具有高电阻率晶界层,提高了铁氧体晶界的电阻率,降低了铁氧体的涡流损耗。然后,研究了纳米CaCO3和SiO2对MnZn功率铁氧体材料的影响,研究结果表明加入纳米材料有助于MnZn功率铁氧体材料的晶粒均匀生长,并阻止其他杂质离子进入铁氧体材料的晶格,而在晶界层富集,形成高电阻率的晶界层,降低了铁氧体材料的涡流损耗,提高了铁氧体材料的性能。最后,研究了烧结工艺对功率铁氧体材料磁性能的影响,在最佳烧结温度和平衡气氛下烧结可以得到高性能的功率铁氧体。对高磁导率MnZn铁氧体而言,高磁导率的关键在于选择合适的配方和掺杂,并辅于适当的烧结工艺。选择合适的配方,在适当的掺杂和烧结工艺条件下就可以制得为15K的高磁导率MnZn铁氧体材料。适量的有效杂质Bi2O3、MoO3、PbO、Co2O3和B2O3都可以促进铁氧体的晶粒生长,提高烧结密度,并提高磁导率。更多还原

【Abstract】 MnZn ferrite is the key materials of modern electronic industry and information industry. With the rapid development of telecommunication and computer technology, MnZn ferrite is required for better performance. According to application characteristic, MnZn ferrite can be divided into three kinds, power ferrite, high permeability ferrite and EMI ferrite. Now the power ferrite is developing to use in higher frequency with lower power loss. For high permeability ferrite, higher initial permeability with better stability is needed. For this reason, this dissertation presents a deeply study on the preparation technology and mechanism of high properties MnZn ferrite.The magnetic origin of MnZn ferrite can be interpreted by the crystal structure of MnZn ferrite. The relationship between magnetic parameters such as magnetic torque, Courier temperature, saturation magnetic inductin, et al, and magnetic properties of MnZn ferrite have been studied using theory of Neer molecular field. The mechanism of MnZn ferrite magnetic characteristics, such as loss and initial permeability is discussed from the concept of magnetic domain. The methods of lowering power loss and improving the initial permeability are indicated.The preparation technology of MnZn ferrite is discussed. Some aspects of preparation technology should be considered completely. The formation mechanism and solid reaction kinetics of MnZn ferrite is studied. The effect of sintering parameters such as sintering temperature, atmosphere, cooling speed, on the MnZn ferrite magnetic properties is also discussed.The key technology for preparation low power loss MnZn ferrite is added in proper content dopants and sintered under optimal sintering condition. The effect of dopants CaCO3、SiO2、TiO2、ZrO2、Ta2O5、Er2O3 on the magnetic properties of power MnZn ferrite is systematically studied. The results showed that the magnetic loss of MnZn ferrite is lowered with containing proper content dopants in MnZn ferrite. From studying the microstructure of MnZn ferrite contained these dopants, the conclusion is drawn that the <WP=7>dopants atoms are enriched in the grain boundaries and developed a high ρlayer to lower the eddy current loss. The effect of SnO2 on the magnetic properties of MnZn ferrite is also studied. At this moment, the calcinations temperature is decreased. High properties MnZn ferrite is obtained. SnO2 added to MnZn ferrite dissolves in the ferrite grain during sintering and induces an excess amount of Fe2+, which form stable Fe2+-Sn4+ pairs. These pairs do not participate in the hopping mechanism and improve the grainρ. Part Sn4+ ion with the other ion enriched in the grain boundaries and developed a high ρlayer to lower the eddy current loss. The effect of nano-SiO2 and CaCO3 addition on the power loss of MnZn ferrites is investigated ultimately. The MnZn ferrite with nano-dopants can produce uniform grain structure and decrease the hysteresis and eddy current losses. These losses are thought to originate from the additive effect of Si atoms, which are enriched in grain boundaries to form a high resistivity layer and prevent Ca and Nb atoms being incorporated with the spinel lattice. High properties MnZn ferrite can be gained by sintering at optimum sintering temperature and equilibrium atmosphere.The key technology for preparation high initial permeability MnZn ferrite is chosen proper component, added in proper content dopants and sintered under optimal sintering condition. The effect of dopants Bi2O3、Mo2O3、PbO、Co2O3 and B2O3 on the magnetic properties of high permeability MnZn ferrite is systematically studied. The results showed that the permeability and density of MnZn ferrite is increased with containing proper content dopants in high permeability MnZn ferrite, for these dopants can promote grain growth.更多还原