以溶膠-凝膠法製備Ba(3-X)SrXCo2Fe24O41六方晶系鐵氧磁體之特性分析與研究

Abstract

目前積層式磁珠使用的材料以鎳/銅/鋅系之鐵氧磁體為主，應用的頻號頻段約在50MHz以下，但在訊號量增加的情形下訊號頻率上升，在大於50MHz以上之訊號使用鎳/銅/鋅系之材料會造成訊號之衰減過多的情形，而六方晶系鐵氧磁體中的Z型(Ba3Me2Fe24O41)擁有高的共振頻率，可用來做為300~1000MHz之濾波器。本研究旨在以溶膠-凝膠(sol-gel)法合成Co2Z型之六方晶系鐵氧磁體並與傳統固態反應方式做比較，期使以微細粒徑粉末之高表面能，促進燒結使合成溫度能有效降低，並探討佔據相同晶格位置之Ba2+及Sr2+離子在不同莫耳比例時，是否因其離子半徑不同對其合成溫度及磁性質等物理特性產生影響。 研究中發現以溶膠-凝膠法製備之Ba1.5Sr1.5Co2Fe24O41前驅物粉體可得到良好的元素分散效果，製作之粉體以1200oC /2小時煆燒可得到高純度Co2Z型之六方晶系鐵氧磁體，且晶粒尺寸較固態反應法製備的粉體來得小且均勻，此外，以Sr取代Ba時，當Sr︰Ba之mole比是1.5︰1.5，初導磁率最高，此係因為Co2Z相的純度近100%所致，並且由於Sr之離子半徑較Ba小，晶格係數變小，使超交換交互作用增強，因此導磁率上升。本研究以溶膠-凝膠法製備之Ba1.5Sr1.5Co2Fe24O41材料擁有初導磁率約8、矯頑磁力約5~6 Oe的良好磁特性，相當適合做為高頻濾波器的用途。

Present magnetic component manufacturers use Ni/Cu/Zn ferrite materials to fabricate multi-layer chip beads of pass bands under 50 MHz. As the trend of high-transmission speed in electric circuit applications growing, signal frequency becomes higher. When the signal frequency is greater than 50MHz, signal intensity is attenuated by multi-layer chip beads of the Ni/Cu/Zn ferrites. Hexaferrite Co2Z is a ferrite material of high self resonance frequency (SRF), and is suitable for use as a filter at 300~1,000 MHz. In this regard, this research uses a sol-gel method to synthesize hexaferrite Co2Z powders in an aim that uniformly mixed powders with a high surface energy can be prepared to reduce the formation temperature of Co2Z phase. The process, structure and magnetic characteristics of the sol-gel prepared Co2Z powders were compared with that made from traditional solid-state interaction method. Furthermore, addition of Ba2+ and Sr2+ ions of different mole ratios has been conducted and its influence to the formation temperature and magnetic property of Co2Z is examined. The sol-gel method produced homogeneously mixed uniform powder/precursor mixtures; which in turn, resulted in high-purity Co2Z phase at 1200oC with a reduced grain size and a more uniform grain-size distribution than those of the solid-state interaction method. For the case that Sr ions are added to substitute Ba ions with a molar ratio of 1.5 : 1.5, the sol-gel synthesized Co2Z powders showed highest initial magnetic permeability. This finding is presumably due to the high purity 100% of Co2Z synthesized and the small radius of Sr ions in comparison to that of Ba ions so that lattice parameter is smaller to facilitate superexchange interactions. In summary, the sol-gel synthesized Co2Z material presents good magnetic characteristics with an initial permeability of 8 and coercive force of 5~6 Oe, suitable for the high-frequency filter applications.