离子掺杂型钡铁氧体毫米波吸收材料的制备及性能研究

发布时间：2018-05-29 21:47

本文选题：溶胶-凝胶 + 钡铁氧体　；参考：《浙江大学》2017年博士论文

【摘要】：现代通信技术的发展,给人们日常生活带来便利的同时,也引起了电磁污染这一严重环境问题。另外,现代雷达等监测技术的发展,也给军事隐身技术提出了新的要求。由此可见,无论是在民用上为解决电磁污染问题还是在军事上提高隐身能力,对于高性能吸波材料的研究都具有重要意义。一方面,目前,武装直升机载火控雷达大都选择毫米波大气窗口 35GHz作为其工作频率。因而,对于35 GHz频段的高性能吸波材料的研究迫在眉睫。M型钡铁氧体由于自然共振可在一定范围内具有较大的磁损耗,而被广泛用作吸波材料。其自然共振频率约为～45 GHz,利用三价非磁性或者弱磁性离子掺杂取代M型钡铁氧体中的Fe3+,可降低M型钡铁氧体的磁晶各向异性场,从而可降低自然共振峰频率,进而调节吸波频率范围至35 GHz。然而由于这些钡铁氧体的共振形式单一且介电损耗较小,因此吸波频带较窄且匹配厚度较厚,限制了他们的广泛应用。针对以上问题,本文选取了价态较高、半径较大的非磁性或弱磁性离子及离子组合取代钡铁氧体中的Fe3+。一方面,高价离子取代Fe3+时,体系为维持电荷平衡,会有部分的Fe3+转变为Fe2+。Fe3+和Fe2+离子通过交换耦合作用可以形成一个比Fe3+的g因子值(2.00)还要大的新的g因子。体系中多个g因子共存,会在体系中形成多个自然共振峰,进而有望产生多个反射损耗峰,达到宽频吸收的目的。另一方面,半径较大的离子取代Fe3+,会造成晶格膨胀。为缓解这种膨胀,体系中可能会产生一部分氧空位,使体系的电导增加,增加介电常数及损耗。进而降低匹配厚度。本文首先制备了 Nb5+掺杂钡铁氧体BaNbxFe12-xO19,最终使在1350℃烧结3 h后的x=0.6样品在毫米波大气窗口～35 GHz附近,吸波频宽可达～12.0+GHz,RL可达～-54dB,而匹配厚度仅为0.86mm。本文还研究了铌掺杂样品中钡铁氧体相的形成过程,揭示了铌掺杂量及热处理时间对钡铁氧体相的形成温度以及晶粒形貌的影响机理。建立了材料成分和热处理条件与材料电磁参数之间的联系。并通过结合阻抗匹配理论,匹配厚度理论和衰减机理,成功阐明了电磁参数与不同等级的匹配厚度对材料最终吸波性能的控制作用。本文还制备了锆掺杂钡铁氧体BaZrxFe12-xO19。本文用溶胶-凝胶法制备了Zr4+掺杂钡铁氧体,研究了 Zr4+离子在钡铁氧体中取代Fe3+的位置,并分析了占据不同Fe3+位置的Zr4+离子对钡铁氧体中Fe2+和氧空位的浓度影响,并最终对电磁参数及吸波性能的影响。结果表明,当x≤0.1时,Zr4+离子主要占据4f1位置的Fe3+离子,而当x0.1时,Zr4+离子主要占据2b位置的Fe3+离子。当Zr4+离子主要占据4f1位置时,Fe2+和氧空位大量产生,介电常数提高显著;而当Zr4+离子主要占据2b位置时,Fe2+浓度基本保持不变而氧空位浓度减小,介电常数逐渐降低。在x≥0.2样品中可出现2个RL峰最终,x=0.2的样品可在毫米波大气窗口～3 5 GHz附近的吸波频宽可达～10 GHz,RL可达～-40 dB,而同时匹配厚度仅为～0.8 mm。由于Nb5+,Zr4+离子单掺杂样品中,取代Fe3+离子的量有限。使得这种宽频,高强和薄厚度的高性能吸波材料可应用的频段较窄,约为24～40GHz。为了使这种宽频和薄厚度的高性能吸波材料,可应用于更多频段,本文利用溶胶-凝胶法制备了 Nb5+-Ni2+离子共掺杂钡铁氧体。采用Nb5+-Ni+离子共掺是想通过降低掺杂离子的平均价态与Fe3+离子的价态差,从而增加Fe3+离子的掺杂量,进而达到拓宽应用频段的目的。并分析了实验加入的Nb5+和Ni2+的离子量与实际进入钡铁氧体晶格并取代Fe3+离子的Nb5+和Ni2+的离子量的关系。结果表明,烧结过程中Ni2+易反应生成容易挥发的Ni(CO)4,会造成Ni2+的损失。使取代了 Fe3+离子的Nb5+和Ni2+离子的比要比实验加入的Nb5+和Ni2+离子的比大。铌镍离子共掺杂钡铁氧体在匹配厚度为(～1mm)时,吸收频宽可达(～11 GHz),吸波强度约为(～-20 dB);且具有更广的可调制频谱范围(18 GHz～40 GHz),是一种极具潜力的吸波材料。另一方面,考虑到Zr4+离子半径大于Fe3+离子,会造成晶格膨胀;而Ti4+离子半径小于Fe3+离子,会造成晶格收缩。若采用Zr4+-Ti4+离子共掺,通过这两种离子对晶格造成的相反作用相互抵消,从而有望增加Fe3+离子的掺杂量,进而达到拓宽应用频段的目的。因此本文还利用溶胶-凝胶法制备了 Zr4＋-Ti4+离子共掺杂钡铁氧体吸波粉体。研究了 Zr4+-Ti4+掺杂量及烧结温度对钡铁氧体相结构,形貌,电磁性能和吸波性能的影响。结果表明,在1300℃～1400℃烧结3h后,x=0～0.4的样品中可形成单相的钡铁氧体。晶粒尺寸随着烧结温度的增加而逐渐增大,随着掺杂量的增加先减小后增大。介电常数随着温度提高而逐渐增加而随着掺杂量增加先增大后逐渐减小。最终,当烧结温度为1400℃且x≥0.2时,锆钛共掺杂钡铁氧体的RL可达～50dB,BW宽达～12GHz及以上,而dm仅为～1mm。并且,随着掺杂量的增加,有效吸波频率可以迅速的从40+GHz调制到18-GHz。
[Abstract]:The development of modern communication technology has brought convenience to people's daily life, but also caused the serious environmental problem of electromagnetic pollution. In addition, the development of modern radar monitoring technology has also put forward new requirements for military stealth technology. This can be seen, whether it is in civilian use to solve electromagnetic pollution problems or military improvement. Body ability is of great significance for the research of high performance absorbing materials. On the one hand, at present, most of the armed helicopter fire control radar selects the millimeter wave air window 35GHz as its working frequency. Therefore, the study of the high performance absorbing materials of the 35 GHz frequency band is imminent for the natural resonance of the.M type barium ferrite due to the natural resonance range. It has large magnetic loss and is widely used as a absorbing material. Its natural resonance frequency is about 45 GHz. The magnetic anisotropy field of M type barium ferrite can be reduced by replacing Fe3+ in M type barium ferrite by using trivalent nonmagnetic or weakly magnetic ions, which can reduce the frequency of spontaneous resonance peak, and then adjust the frequency range of wave absorption to 35. GHz., however, because the resonance forms of these barium ferrite are single and the dielectric loss is small, so the absorption band is narrow and the matching thickness is thicker, so their wide application is limited. In this paper, the higher valence state, the larger radius of the nonmagnetic or weak magnetic ion and the ion combination are selected to replace the Fe3+. in the barium ferrite. When high valence ions replace Fe3+, in order to maintain the charge balance, a partial Fe3+ transformation to Fe2+.Fe3+ and Fe2+ ions can form a new g factor larger than the g factor of Fe3+ (2). The coexistence of multiple g factors in the system will form multiple natural resonance peaks in the system, and may lead to a number of reactions. In order to alleviate this expansion, some oxygen vacancies may be produced in the system to increase the conductivity of the system, increase the dielectric constant and loss of the Fe3+, and then reduce the matching thickness. In this paper, the Nb5+ doped barium ferrite BaNb was first prepared. XFe12-xO19, when the x=0.6 samples were sintered at 1350 C for 3 h in the millimeter wave atmosphere window to 35 GHz, the wavelength of the absorbing wave can reach to 12.0+GHz and RL can reach to -54dB, and the matching thickness is only 0.86mm.. The formation process of the barium ferrite phase in the niobium doped samples is also studied. The relationship between the temperature and the morphology of the grain is formed. The relation between the material composition and the heat treatment conditions and the electromagnetic parameters of the material is established. By combining the theory of impedance matching, the matching thickness theory and the attenuation mechanism, the control effect of the matching thickness of the electromagnetic parameters and the different grades on the ultimate absorbing property of the material is clarified. The zirconium doped barium ferrite BaZrxFe12-xO19. was prepared in this paper to prepare Zr4+ doped barium ferrite by sol-gel method. The position of Zr4+ ions in the substitution of Fe3+ in barium ferrite was studied. The influence of Zr4+ ions occupying different Fe3+ positions on the concentration of Fe2+ and oxygen vacancies in barium ferrite was analyzed, and the electromagnetic parameters and absorption properties were finally obtained. The results show that when x is less than 0.1, the Zr4+ ion mainly occupies the Fe3+ ion of the 4F1 position, and when x0.1, the Zr4+ ions mainly occupy the Fe3+ ions of the 2B position. When the Zr4+ ions occupy the 4F1 position, the Fe2+ and oxygen vacancies are produced and the dielectric constant increases significantly. The oxygen vacancy concentration decreases and the dielectric constant decreases gradually. 2 RL peaks can be found in X more than 0.2 samples. The sample of x=0.2 can reach to 10 GHz in the millimeter wave atmosphere window to 35 GHz, and RL can reach to -40 dB, while the matching thickness is only 0.8 mm. due to Nb5+, Zr4+ ion single doped samples, and the amount of substituted Fe3+ ions. Limited. The frequency band of high performance absorbing materials with wide frequency, high strength and thin thickness can be applied narrowly. It is about 24 ~ 40GHz. to make this kind of high performance absorbing material with wide frequency and thin thickness can be applied to more frequency bands. In this paper, Nb5+-Ni2+ ions Co doped barium ferrite is prepared by sol-gel method. The co doping of Nb5+-Ni+ ions is used in this paper. By reducing the average valence state of the doped ions and the difference of the valence state of Fe3+ ions, the doping amount of Fe3+ ions is increased, and then the purpose of broadening the application band is achieved. The relationship between the ionic quantity of the experimental Nb5+ and Ni2+ with the actual entry of the lattice of the barium ferrite and the amount of the ions of the Nb5 + and Ni2+, which is replaced by the Fe3+ ion, is analyzed. During the process, Ni2+ easily reacts to produce volatile Ni (CO) 4, which will cause the loss of Ni2+. The ratio of Nb5+ to Ni2+ ions that replace the Fe3+ ions is larger than that of the Nb5+ and Ni2+ ions added to the experiment. The absorption bandwidth of the niobium ions Co doped barium ferrite can reach (~ 11 GHz) when the matching thickness is (~ 1mm), and the absorption intensity is about (-20); And with a wider range of modulation spectrum range (18 GHz to 40 GHz), it is a potential absorbing material. On the other hand, the lattice expansion will be caused by the Zr4+ ion radius greater than the Fe3+ ion, while the radius of the Ti4+ ion is smaller than the Fe3+ ion, which will cause the lattice contraction. If the Zr4 +-Ti4+ ions are Co doped, the lattice is caused by the two ions. The opposite action counteracts each other, thus it is expected to increase the doping amount of Fe3+ ions and expand the application band. Therefore, the Zr4 + -Ti4+ ion Co doped barium ferrite absorption powder has been prepared by the sol-gel method. The structure, morphology, electromagnetic properties and absorption of Zr4+-Ti4+ doping amount and sintering temperature on barium ferrite are studied. The results show that the single phase barium ferrite can be formed in x=0 ~ 0.4 samples after sintering at 1300 to 1400 C for 3h. The grain size increases with the increase of the sintering temperature. The dielectric constant increases with the increase of the doping amount. Finally, when the sintering temperature is 1400 and x > 0.2, the RL of the zirconium and titanium Co doped barium ferrite can reach 50dB, the BW is as wide as 12GHz and above, and the DM is only 1mm., and the effective wave frequency can be quickly modulated from 40+GHz to 18-GHz. as the amount of doping increases.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB34

【参考文献】