【作者】 贺强；

【导师】 姚斌；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2011， 博士

【摘要】 Ba-Fe-O铁氧体作为一种磁性材料,它的发展吸引了很多人的注意,铁氧体磁性材料以其优异的磁性能和价格优势在磁性材料的研究和发展中占有举足轻重的地位,并引起研究者广泛的兴趣。Ba-Fe-O铁氧体在微波毫米波器件,高密度磁记录介质以及医疗等领域已被广泛地应用。例如可以作为隐形飞机和无人侦察机表面的涂层,进行微波的吸收,达到隐形的目的；还可以作为药物载体的磁靶,使药物发挥更好的治疗效果。为了更好地发挥Ba-Fe-O铁氧体的应用价值,对于研究者来说如何更进一步提高其矫顽力,优化其磁性能,探讨其形成机制,调控掺杂元素的掺杂状态任重道远。研究工作对促进Ba-Fe-O铁氧体的应用和丰富磁性理论有重要意义。Ba-Fe-O铁氧体的结构主要有三种类型：尖晶石型、磁铅石型(M型)和石榴石型。尖晶石铁氧体是一种软磁材料,广泛地应用于高密度磁记录、微波装置和磁流体等领域。尖晶石铁氧体结构的化学通式为：AB2O4,为面心立方结构,晶胞中含有许多四面体和八面体空位间隙,这些空位的存在为改进铁氧体性能提供了条件,为金属离子的掺杂和取代创造了条件,因而使尖晶石型铁氧体种类繁多,性能更加优异。M型Ba-Fe-O铁氧体材料是一种永磁材料,为硬磁材料,广泛用于磁记录,发动机马达以及电磁波吸收材料等。M型钡铁氧体具有宽磁滞回线、高的矫顽力、单轴磁晶各向异性、优良的旋磁特性、高的化学稳定性、高居里温度和高剩磁等特点,同时具有较高的性价比。近些年随着合成技术和手段的不断创新提高,通过掺杂不同的元素和采取不同的方法研究铁氧体合成过程中结构和相变的报道很多,由于机械合金法做为一个合成磁性纳米材料的主要手段,应用越来越广泛,且机械合金化由于反应复杂,材料配比和球磨能量不同,导致产生结构相变情况也不同。因此,可以形成高性能的纳米磁性前驱体粉末。甘氨酸硝酸盐法又称自蔓延高温合成法,是近二三十年兴起的制备材料的方法,属于一种高新技术。烧结合成出铁氧体粉末性能稳定和尺寸分布均匀等,且燃烧合成前驱体颗粒较小,比表面积大,反应活性高,可用于制造高性能的铁氧体。采用机械合金法进行Ba-Fe-O铁氧体的合成,通过球磨BaCO3和α-Fe2O3,首次制备出尖晶石结构BaxFe3-xO4相。研究表明：在球磨过程中,首先形成了α-(Fe,Ba)2O3固溶体,随着球磨时间的增加,Ba在α-(Fe,Ba)2O3中的固溶量增加,当Ba含量达到一定的固溶限时,α-(Fe,Ba)2O3转变为具有较高密度的BaxFe3-xO4尖晶石相。在BaxFe3-xO4中,Ba2+替代Fe2+占据尖晶石结构中八面体的B位,其成份为Ba0.23Fe2.77O4,饱和磁化强度为53.3emu/g,矫顽力是113.7 Oe。利用常规烧结、机械合金化结合高温烧结和甘氨酸硝酸盐法开展了M型钡铁氧体(M-BaFe12O19)的制备、表征和磁性能的研究工作,并利用烧结曲线研究了不同制备方法中M-BaFe12O19的形成机理。研究结果表明：以α-Fe2O3和BaCO3为原材料,利用常规烧结制备M-BaFe12O19过程中,首先是α-Fe2O3和BaCO3反应生成具有正交结构的BaFe2O4中间相,然后BaFe2O4与α-Fe2O3在770至920℃温度之间反应,烧结形成M-BaFe12O19.在机械合金化结合高温烧结法中,首先将α-Fe2O3和BaCO3的混合物球磨80h形成尖晶石结构的BaxFe3-xO4,然后将BaxFe3-xO4在700-1000℃退火2小时,形成M-BaFe12O19.在甘氨酸硝酸盐方法中,首先通过自蔓延反应生成了α-Fe2O3,Fe3O4和BaFe2O4混合的前驱体粉末,然后通过在1000℃条件下烧结前驱体粉末制备出了单一相的M-BaFe12O19。比较三种制备方法,以尖晶石结构BaxFe3-xO4为前驱体通过烧结制备M-BaFe12O19的最低形成温度最低。研究发现,以机械合金法制备的M-BaFe12O19的饱和磁化强度和矫顽力分别是47.24emu/g和5086.340e,其矫顽力比其它两种方法制备的M-BaFe12O19的矫顽力大。矫顽力的增大不是由于晶粒尺寸和纯度所造成的,而是由于Ba离子残留在八面体2a位置上的原因。利用甘氨酸硝酸盐法进行了Al、Dy及La掺杂M-BaFe12O19的制备和掺杂元素对钡铁氧体的结构和矫顽力的影响规律和机制的研究工作。研究结果表明：当燃料和氧化物比为1.5：1时,前驱体粉末经900℃烧结2h形成单一M-BaFe12O19相。因此,所有掺杂都是在这一比例下进行的。对于A1掺杂,A1在M-BaFe12O19中Al3+替代Fe3+,记作BaAlxFe12-xO19。XRD测试结果表明：当0<x≤4时,随着Al3+含量的增加,衍射角向高角移动,这归因于Al3+半径小于Fe3+的结果。计算结果表明掺杂对晶格常数a影响较大,a值从5.887A下降到5.819A,对晶格常数c影响趋势相同。另外,XRD峰的半高宽随A1掺杂量的增加而增加,即晶粒尺寸随A1掺杂量增加而减小。这意味着铝的加入减慢了晶粒生长速度。伴随着晶格常数和晶粒尺寸的变化,矫顽力随A1掺杂量的增加从4012 Oe增加到13738 Oe,接近钕铁硼的矫顽力。但是,当x=5时,BaAlxFe12-xO19出现分相,样品由M-BaAlxFe12-xO19.α-Fe2O3和BaAl2O4相组成,同时矫顽力下降到8430 Oe。这意味着A1在M-BaAlxFe12-xO19有限固溶度。由于Al3+在BaAlxFe12-xO19中优先占据2b和12k晶位,替换了该晶位上的Fe3+,使整个钡铁氧体Fe3+磁性离子数减小,因此,随A1掺杂量增加,饱和磁化强度单调降小。对于Dy掺杂,Dy替代Ba,经900℃烧结形成的BaxDy1-xFe12O19结晶较差,矫顽力没有增加反而略有降低,这与文献报道的不一致,可能由于制备方法不同所致。对于La掺杂,La替代Ba形成M-BaxLa1-xFe12O19,在0<x<5范围内,矫顽力随La含量增加基本没有变化,但饱和磁化强度却从x=0的60.4 emu/g逐渐下降到x=0.5的38.6emu/g。由La和A1共掺杂形成的M-Ba0.5La0.5AlFe11O19,矫顽力为8704 Oe,饱和磁化强度为26.7emu/g。其矫顽力高于BaAlFe11O19的6679 Oe。以上结果表明：对于M型BaFe12O19来说,其矫顽力的提高主要来自对Fe3+的替代掺杂,而替代Ba2+的掺杂形式对矫顽力的影响较小。更多还原

【Abstract】 As a kind of magnetism materials, the development of Ba-Fe-O ferrite attracts many people’s notice, ferrite magnetic materials occupy important status in magnetism study and development for excellent magnetism performance and cheap price, and bring broad interest to investigator. Ba-Fe-O ferrites had been applied extensively in mircrowave and millimeterwave device, high density magnetic recording and medical cure field etc. For example, they were made of coats of latent aeroplane and scout without people, airplane obtain aim of conceal themselves by absorbed microwave. In order to bring to applied value mostly from Ba-Fe-O, The task is arduous for improving cocercive, optimizing magnetic performance, studying form mechanism and controling adulteration element state. Our present study work was significant in advanced Ba-Fe-O ferrites and enrich magentism theory.Ba-Fe-O ferrites have three kinds structure:spinel type, magnetoplumbite type(M type) structure and garnet type structure. Spinel ferrite was a kind of soft magnetic material, it widely used high density magnetic recording materials, microwave devices (MW) and magnetic fluid etc. The chemical formula of structure was AB2O4, belong to facecenter cubic structure, many tetrahedral and octahedral interspaces in crystal cells, these interspaces offer changes for improving magnetism performance of ferrite, also created conditions for adulteration and substitution of metal ionic, so many kinds of spinel ferrites have appeared, their performancs were excellent. As a forevermagetic material of M type Ba-Fe-O ferrites was hard magnetic material, widely used in magnetic recording, engine motor and absorbing electromagnetic wave materials etc. It possess many characteristic, such as wide hysteresis curve, high coercivity, single axial magnetic crystal anisotropy, excellent spin magenitsm performance, high stability of chemistry, high curie temperature, high remanence and high quality to price ratio etc.In recently years, some synthesis technologies improve gradually, some reports of structures and phase changes for synthesis process about adulterating elements and adopted different methods appeared a large number, mechanical alloy method was used abroadly as a synthesis magnetic nanometer material mode, because the reaction of mechanical alloy was complex, so different structure phase changes were happened for different material ratios and milling energies. So high performance precursor nanometer powders were perpared by ball milling. Glycin nitrate method also called self-combustion high temperature synthesis, was arise in recently twenty-thirty years, it is a kind of new technologies. The performances of samples which were prepared by this method were stable and sizes distributed uniformity, at the same time the grain of producation for combustion synthesis was small and relative surface was large, the reaction character was high, so high performance ferrites could be prepared by this method.Ba-Fe-O ferrites was synthesized in mechanical alloy method, BaxFe3_xO4 with spinel structure was fabricated by ball milling BaCO3 andα-Fe2C>3 powders for the first time. The result of study show that, theα-(Fe,Ba)2O3 solid solubility body was formed in the milling process firstly, the Ba content in theα-(Fe,Ba)2O3 increased with increasing milling time, when the Ba content exceeded a limited solubility, theα-(Fe,Ba)2O3 transformed into a high density phase of BaxFe3_xO4 with spinel structure, in which the Fe2+was substituted Ba2+occupied an octahedral site. The composition of production was Ba0.23Fe2.77O4, the saturation magnetization was 53.3emu/g and coercivity was 113.7Oe.The research work for preparation, characteristic and magnetism performance of M type barium hexaferrite (M-BaFe12O19) were developed in general sinter method, mechanical alloy method and Glycin nitrate method. Then, the form mechanism of M-BaFe12O19 which were prepared in different methods was studied by sintering curve. The study result show in the process of preparing M-BaFe12O19 with a-Fe2O3 and BaCO3 as raw and processed materials in general sinter method, fistly the a-Fe2O3 reacted with BaCO3 to form Orthorhombic BaFe2O4 middle phase, then the BaFe2O4 reacted with a-Fe2O3 to form M-BaFe12O19 in a sintering temperature ranging from 770 to 920℃. However, in mechanical alloy method, the a-Fe2O3 reacted with BaCO3 to form BaxFe3-xO4 with spinel structure, while the M-BaFe12O19 was obtained by annealing the BaxFe3-xO4 at 700-1000℃. In the glycin-nitrate procedure, the precursor powders containing a-Fe2O3, Fe3O4 and BaFe2O4 were fabricated by self-propagating reaction firstly, and then the single M-BaFe12O19 was produced by sintering the precursor powders at 1000℃. The form temperature of M-BaFe12O19 which was sintered for precursor powders of BaxFe3-xO4 with spinel structure was lowest. We find that saturation magnetization and the coercivity of the M-BaFe12O19 which was fabricated by mechanical alloy method were 47.24 emu/g and 5086.34 Oe, respectively, which were much larger than those of the M-BaFe12O19 produced by other two procedures. The cause was Ba ion occupied octahedral 2a site, it was independent of grain sizes and purity.M-BaFe12O19 was prepared by Al3+, Dy3+and La3+substituted in Glycin-nitrate method, at the same time we study the law and mechanism which were influenced of adulteration element. The result show that, single phase M-BaFe12O19 was prepared at 900℃when fuel and oxide ratio was 1.5:1. Therefor all of adulterations were done in this proportion. Al3+substituted Fe3+in the process of Al adulterated M-BaFe12O19, it marked BaAlxFe12-xO19. XRD results indicate that the diffraction angle moved toward high angle direction when x of BaAlxFe12-xO19 increases from 0 to 4, the cause was the radius of Al3+is smaller than radius of Fe3+. The calculation result indicate adulteration influence crystal lattice a greatly, the value of a dropped from 5.887 A to 5.189 A, the change trend of crystal lattice c was same. Otherwise the FWHM (full width at half maximum) increases when adulteration quantity of AI increase, namely crystal grain size decreased when adulteration quantity of Al increased. This result account for growth speed of crystal grains was slower because of Al adulteration. The coercive force increased from 4012 Oe to 13738 Oe along with changes of crystal lattice constant and crystal grain size, it almost equal to the coercive of Nd-Fe-B. But when x up to 5, the other impurity phases appeared, the sample was made of M-BaAlxFe12-xO19, a-Fe2O3 and BaAl2O4 the coercive force declines to 8430 Oe. It indicate solid solubility of Al in BaAlxFe12-xO19 was limited. Because Al lock-in 2b and 12k site of M-BaAlxFe12-xO19 firstly, substituted Fe3+of this site, cause to decrease of magnetism Fe3+ion number, so the saturation magnetization reduces monotonously along with adulteration quantity of Al increases. When Ba was substituted by Dy, the crystal quality of BaxDy1-xFe12O19 sintered at 900℃was not good, Coercive forces did not increased for the sample of BaxDy1-xFe12O19. it decreased a little on the contrary, that was different from literature report, the cause might be different preparation method. M-BaxLa1-xFe12O19, was prepared when Ba was substituted by La, x changes from 1 to 5 range, The changes of coercive forces was not obvious, but the saturation magnetization reduces from 60.4 emu/g when x equal to 0 to 38.6 emu/g when x equal to 0.5. M-Bao.5La0.5AlFe12O19 was prepared when La and Al together adulterate, coercive foerce was 8740 Oe higher than 6679 Oe of BaAIFe11O19, the saturation magnetization was 26.7 emu/g. The anterior result show:the coercive force improvement of M-BaFe12O19come from substituting Fe3+, the method of substituted Ba2+was secondary.更多还原