【作者】 李媛；

【导师】 吴顺华；

【作者基本信息】 天津大学 ， 微电子学与固体电子学， 2007， 硕士

【摘要】 本论文以BaO-Nd₂O₃-TiO₂（简称BNT系统）微波介质陶瓷系统为对象,通过对A位Nd³⁺离子、B位Ti⁴⁺离子置换或两相复合的方法对其晶体结构和微结构进行调整,实现介电性能的最优化。一是以Bi₂O₃为添加剂,通式采用Ba_6-3x(Nd_1-yBiy)_8+2xTi₁₈O₅₄（x =3/2）组成,研究了晶体微结构与介电性能之间的关系。当y值增大时,介电常数迅速增大,介电损耗增加,微波性能Q值有所下降。掺入Bi₂O₃之后系统中出现的具有高介电常数的Bi₄Ti₃O₁₂第二相为介电常数的增大起了重要作用。与Nd³⁺离子半径相近的Bi³⁺取代部分Nd³⁺离子或占据空隙较大的A1和A2位置使得类钨青铜结构的BNT系统形成了类填满型钨青铜结构。而且,当Bi含量增加时,单胞体积增大, Ti⁴⁺自发极化增强,体系内部结构系数的变化也加强了内电场,在整体上表现为介电常数随Bi含量的增加呈线性趋势。介电损耗tgδ增大,微波参数Q值减小可从两方面进行解释,一方面增强的极化作用消耗了更多的电场能;另一方面是在烧结过程中形成的少量复合相使衰减因子γ增大,Q值降低。温度系数αc随Bi₂O₃含量的增加先正向变化随后向负向发展,原因在于Bi³⁺取代Nd³⁺将导致更加严重的Ti-O八面体扭曲,使得αc先正向变化。但在Bi含量达到一定量时（y=0.25左右）,αc值下降,可能与介质中产生的第二相和较多的液相有关。二是以Ta2O5为添加剂,选取Ba₄Nd₂Ti₄Ta₆O₃₀和Ba₅NdTi₃Ta₇O₃₀化学分子式作为出发点,研究了Ta₂O₅和TiO₂对系统介电性能的影响。随着Ta₂O₅含量的增加,介电常数明显增大,介电损耗变化不大,均在5×10-4左右,但温度系数将变得更负。随着TiO₂含量从0.3增加到0.8（分子摩尔比）,系统的介电常数先减小再增加,然后再减小,整体呈下降趋势;介电损耗和温度系数随着TiO₂含量的增多变化不大,该现象的出现与Ba₅NdTi₃Ta₇O₃₀属于填满型钨青铜结构有关,且与TiO₂本身介电常数偏小,且为四方相有很大联系。在整个实验中,得到的性能优异的微波介质陶瓷材料为:ε≈120, tgδ=2.36x10^-4（测试频率为1MHz）,Q≈4600 （测试频率为1GHz）,αc=-24ppm/℃（添加剂为Bi₂O₃）。ε≈96, tgδ=0.69x10^-4（测试频率为1MHz）,αc=5.6723ppm/℃（添加剂为Bi₂O₃）。ε=103,tgδ=5.32x10-4（测试频率为1MHz）,αc=-760.763ppm/℃（添加剂为Ta₂O₅）。更多还原

【Abstract】 In this paper, the BaO-Nd₂O₃-TiO₂ system（BNT system for short） is studied and improved. The optimazation of BNT system dielectric properties is achieved by adjusting its crystal and micro- structure through the substitution for A site or B site or composite phases.1. Bi₂O₃ for additive. It is adopted Ba_6-3x(Nd_1-yBiy)_8+2xTi₁₈O₅₄（x=3/2） as molecular formula. The dielectric properties and micro-structure, also the relationship between them are studied. It is indicated that the dielectric constant increases greatly whereas Q value decreases with the increase of y value. The second phase Bi4Ti3O12 having highεwhich appears after doping with Bi₂O₃ contributes the most to the increase ofε. Bi³⁺ whose ion radius is similar to Nd³⁺ will substitute for part of Nd³⁺ or occupy A1 sites and A2 sites which have larger space, which makes BNT system doping with Bi₂O₃ change to full-filled tungsten bronze-like structure. Furthermore, the cell volume will increase and the spontaneous polarization of Ti4+ ions will be strengthened when the content of BiO₂ increases. Besides, the modification of structure coefficient inside enhances the inner electric field. So the dielectric constant shows linear increase with Bi₂O₃’s content increase. Why the dissipation factor increases and Q value decreases can be explained from two aspects. On the one hand, the strengthened polarization costs more energy. On the other hand, the few composite phases formed during sintering procedure cause the attenuation factorγincreases then Q value decreases. Temperature coefficientαc changes towards positive direction firstly then negative direction with the increase of Bi₂O₃. It is because Bi³⁺’s substitution for Nd³⁺ will cause worse distortion which makesαc increase. However, when Bi₂O₃’s content reaches to a certain level（y equals to 0.25 around）,αc decreased, this phenomenon should be related to the second phase and the liquid phase.2. Ta2O5 for additive. It is started with the molecular formulas of Ba4Nd2Ti4Ta6O30 and Ba5NdTi3Ta7O30. The effect of Ta2O5 and TiO₂ on the system is researched. The dielectric constant increases greatly while the dissipation factor changes a little around 5×10-4 along with the content of Ta2O5 increases, whereas the temperature coefficient changes towards negative direction.When the content of TiO₂ increase from 0.3 to 0.8（molecule mole ratio）,εdecreases firstly then increases, and then dereases again, which shows dereasing trend as a whole. Dielctric dissipation and temperature coefficient changes not too much. All the phenomen should have something to do with the full-filled tungsten bronze structure of Ba5NdTi3Ta7O30 and the tetragonal phase of TiO₂ which has low dielectric constant.During the whole experiment, the microwave dielectric ceramic materials having excellent dielectric properties are prepared, which main dielectric pamameters are listed below:ε≈120, tgδ=2.36x10-4（f=1MHz）,Q≈4600 （f=1GHz）,αc=-24ppm/℃,（Bi₂O₃ for additive）。ε≈96, tgδ=0.69x10-4（f=1MHz）,αc =5.6723ppm/℃（Bi₂O₃ for additive）。ε=103,tgδ=5.32x10-4（f=1MHz）,αc =-760.763ppm/℃（Ta2O5 for additve）。更多还原