本文選題：溶膠-凝膠 + 鋇鐵氧體�。� 參考：《浙江大學》2017年博士論文

【摘要】：現代通信技術的發(fā)展,給人們日常生活帶來便利的同時,也引起了電磁污染這一嚴重環(huán)境問題。另外,現代雷達等監(jiān)測技術的發(fā)展,也給軍事隱身技術提出了新的要求。由此可見,無論是在民用上為解決電磁污染問題還是在軍事上提高隱身能力,對于高性能吸波材料的研究都具有重要意義。一方面,目前,武裝直升機載火控雷達大都選擇毫米波大氣窗口 35GHz作為其工作頻率。因而,對于35 GHz頻段的高性能吸波材料的研究迫在眉睫。M型鋇鐵氧體由于自然共振可在一定范圍內具有較大的磁損耗,而被廣泛用作吸波材料。其自然共振頻率約為～45 GHz,利用三價非磁性或者弱磁性離子摻雜取代M型鋇鐵氧體中的Fe3+,可降低M型鋇鐵氧體的磁晶各向異性場,從而可降低自然共振峰頻率,進而調節(jié)吸波頻率范圍至35 GHz。然而由于這些鋇鐵氧體的共振形式單一且介電損耗較小,因此吸波頻帶較窄且匹配厚度較厚,限制了他們的廣泛應用。針對以上問題,本文選取了價態(tài)較高、半徑較大的非磁性或弱磁性離子及離子組合取代鋇鐵氧體中的Fe3+。一方面,高價離子取代Fe3+時,體系為維持電荷平衡,會有部分的Fe3+轉變?yōu)镕e2+。Fe3+和Fe2+離子通過交換耦合作用可以形成一個比Fe3+的g因子值(2.00)還要大的新的g因子。體系中多個g因子共存,會在體系中形成多個自然共振峰,進而有望產生多個反射損耗峰,達到寬頻吸收的目的。另一方面,半徑較大的離子取代Fe3+,會造成晶格膨脹。為緩解這種膨脹,體系中可能會產生一部分氧空位,使體系的電導增加,增加介電常數及損耗。進而降低匹配厚度。本文首先制備了 Nb5+摻雜鋇鐵氧體BaNbxFe12-xO19,最終使在1350℃燒結3 h后的x=0.6樣品在毫米波大氣窗口～35 GHz附近,吸波頻寬可達～12.0+GHz,RL可達～-54dB,而匹配厚度僅為0.86mm。本文還研究了鈮摻雜樣品中鋇鐵氧體相的形成過程,揭示了鈮摻雜量及熱處理時間對鋇鐵氧體相的形成溫度以及晶粒形貌的影響機理。建立了材料成分和熱處理條件與材料電磁參數之間的聯系。并通過結合阻抗匹配理論,匹配厚度理論和衰減機理,成功闡明了電磁參數與不同等級的匹配厚度對材料最終吸波性能的控制作用。本文還制備了鋯摻雜鋇鐵氧體BaZrxFe12-xO19。本文用溶膠-凝膠法制備了Zr4+摻雜鋇鐵氧體,研究了 Zr4+離子在鋇鐵氧體中取代Fe3+的位置,并分析了占據不同Fe3+位置的Zr4+離子對鋇鐵氧體中Fe2+和氧空位的濃度影響,并最終對電磁參數及吸波性能的影響。結果表明,當x≤0.1時,Zr4+離子主要占據4f1位置的Fe3+離子,而當x0.1時,Zr4+離子主要占據2b位置的Fe3+離子。當Zr4+離子主要占據4f1位置時,Fe2+和氧空位大量產生,介電常數提高顯著;而當Zr4+離子主要占據2b位置時,Fe2+濃度基本保持不變而氧空位濃度減小,介電常數逐漸降低。在x≥0.2樣品中可出現2個RL峰最終,x=0.2的樣品可在毫米波大氣窗口～3 5 GHz附近的吸波頻寬可達～10 GHz,RL可達～-40 dB,而同時匹配厚度僅為～0.8 mm。由于Nb5+,Zr4+離子單摻雜樣品中,取代Fe3+離子的量有限。使得這種寬頻,高強和薄厚度的高性能吸波材料可應用的頻段較窄,約為24～40GHz。為了使這種寬頻和薄厚度的高性能吸波材料,可應用于更多頻段,本文利用溶膠-凝膠法制備了 Nb5+-Ni2+離子共摻雜鋇鐵氧體。采用Nb5+-Ni+離子共摻是想通過降低摻雜離子的平均價態(tài)與Fe3+離子的價態(tài)差,從而增加Fe3+離子的摻雜量,進而達到拓寬應用頻段的目的。并分析了實驗加入的Nb5+和Ni2+的離子量與實際進入鋇鐵氧體晶格并取代Fe3+離子的Nb5+和Ni2+的離子量的關系。結果表明,燒結過程中Ni2+易反應生成容易揮發(fā)的Ni(CO)4,會造成Ni2+的損失。使取代了 Fe3+離子的Nb5+和Ni2+離子的比要比實驗加入的Nb5+和Ni2+離子的比大。鈮鎳離子共摻雜鋇鐵氧體在匹配厚度為(～1mm)時,吸收頻寬可達(～11 GHz),吸波強度約為(～-20 dB);且具有更廣的可調制頻譜范圍(18 GHz～40 GHz),是一種極具潛力的吸波材料。另一方面,考慮到Zr4+離子半徑大于Fe3+離子,會造成晶格膨脹;而Ti4+離子半徑小于Fe3+離子,會造成晶格收縮。若采用Zr4+-Ti4+離子共摻,通過這兩種離子對晶格造成的相反作用相互抵消,從而有望增加Fe3+離子的摻雜量,進而達到拓寬應用頻段的目的。因此本文還利用溶膠-凝膠法制備了 Zr4＋-Ti4+離子共摻雜鋇鐵氧體吸波粉體。研究了 Zr4+-Ti4+摻雜量及燒結溫度對鋇鐵氧體相結構,形貌,電磁性能和吸波性能的影響。結果表明,在1300℃～1400℃燒結3h后,x=0～0.4的樣品中可形成單相的鋇鐵氧體。晶粒尺寸隨著燒結溫度的增加而逐漸增大,隨著摻雜量的增加先減小后增大。介電常數隨著溫度提高而逐漸增加而隨著摻雜量增加先增大后逐漸減小。最終,當燒結溫度為1400℃且x≥0.2時,鋯鈦共摻雜鋇鐵氧體的RL可達～50dB,BW寬達～12GHz及以上,而dm僅為～1mm。并且,隨著摻雜量的增加,有效吸波頻率可以迅速的從40+GHz調制到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.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TB34

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