【作者】 余晓华；

【导师】 周东祥；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 论文概述了微波介质陶瓷体系尤其是BaO-Ln₂O₃-TiO₂体系的研究现状。BaO-Ln₂O₃-TiO₂体系的有效电场分析表明高介电常数的根源在于电子-离子位移极化耦合,A位阳离子对介电常数的影响并不大; BaO-Ln₂O₃-TiO₂体系本征损耗分析结果则表明阳离子的有序分布和八面体倾斜角的增大有利于损耗的降低以及热稳定性的增强。鉴于以上两点,镧系元素对BaO-Ln₂O₃-TiO₂体系的改性研究主要集中在镧系离子对晶体结构和介电性能的影响。论文最后对BaO-Ln₂O₃-TiO₂体系的改性实例和特例进行了实验研究,以验证前述的规律总结。BaO-Ln₂O₃-TiO₂（Ln = La, Pr, Nd, Sm, Gd）微波介质陶瓷的主晶相Ba_6-3xLn_8+2xTi₁₈O₅₄固溶体属于有限置换型固溶体。XRD物相分析和晶胞参数计算结果表明各体系的固溶限分别为:Ln=La时0 .1≤x≤0.8;Ln=Pr时0 .1≤x≤0.8;Ln=Nd时0 .2≤x≤0.7;Ln=Sm时0 .3≤x≤0.7;Ln=Gd时x=0.5。随着镧系离子半径的增大,体系的固溶限逐渐减小,直至唯一取值。在BaO-Ln₂O₃-TiO₂体系中,当稀土元素含量一定时,随着Ln3+离子半径的增大,晶胞在垂直于C轴的ab平面上扩张,晶胞参数主要表现为a和b的增大,c的增幅较小;当稀土元素种类确定时,随着Ln3+含量的增加,Ba_6-3xLn_8+2xTi₁₈O₅₄固溶体的晶胞参数逐渐减小,晶胞体积出现收缩。此外Ba_6-3xLn_8+2xTi₁₈O₅₄固溶体中稀土阳离子半径的减小会增大钛氧八面体的倾斜角,从而导致晶胞体积的减小。稀土元素的离子半径、离子含量、电负性、极化率等因素对BaO-Ln₂O₃-TiO₂体系的微波介电性能也会产生影响。类钙钛矿钨青铜结构使所有的BaO-Ln₂O₃-TiO₂体系具有较高的介电常数,不同的稀土元素则使介电常数在一定的范围内变化。原料配方为Ba_6-3xLn_8+2xTi₁₈O₅₄的BaO-Ln₂O₃-TiO₂体系中,随着镧系元素离子半径、极化率和电负性的增大,介电常数逐渐增大。当x=2/3时,BaO-Ln₂O₃-TiO₂体系均具有最高的品质因数,Ln3+离子半径和电负性越小,品质因数的极值就越大。此外体系的内应力越小,品质因数也越大。在BaO-Ln₂O₃-TiO₂体系中,随着Ln3+离子含量的增加,离子半径的减小,体系结构容忍因子的减小,体系的谐振频率温度系数就更加趋近于零。BaO-Sm2O3-Nd2O3-TiO2复合体系和Bi2O3掺杂改性的BaO-Nd2O3-TiO2体系的晶胞参数变化规律及介电性能变化趋势满足前述规律的变化,验证了镧系元素的存在对BaO-Ln₂O₃-TiO₂体系的改性规律。BaO-CeO2-TiO2体系中由于Ce离子半径偏小及价态不稳定的原因最终无法形成类钙钛矿钨青铜结构的主晶相,成为体系的一个特例,烧结特性和物相组成均与其它体系不同,介电常数和品质因数也较其它BaO-Ln₂O₃-TiO₂体系低。更多还原

【Abstract】 The researching of microwave dielectric ceramics, especially BaO-Ln₂O₃-TiO₂ was summarized in this thesis. The effective electric field analysis in BaO-Ln₂O₃-TiO₂ indicated that it was electron-ion displacement polarization coupling that caused high permitivity. The contribution to polarization of A position cation was not so big. While the analysis results of intrinsic loss of ion crystal indicated that the ordering distribution of the cations in BaO-Ln₂O₃-TiO₂ and the lean angle increment of the octahedron structure were advantaged to loss reduction and heat stability enhancement. Based on the mentioned two points, the modification of BaO-Ln₂O₃-TiO₂ was mainly focused on the effect of lanthanide ion to crystal structure and microwave dielectric properties. At last the modification system and special case of BaO-Ln₂O₃-TiO₂ were examined to identify the antecedent rules.The main part of BaO-Ln₂O₃-TiO₂（Ln = La, Pr, Nd, Sm, Gd）system, i.e., Ba_6-3xLn_8+2xTi₁₈O₅₄ solid solution, belonged to finite substitution solid solution, and the limits were: when Ln=La, 0.1≤x≤0.8; when Ln=Pr, 0.1≤x≤0.8; when Ln=Nd, 0.2≤x≤0.7;when Ln=Sm, 0.3≤x≤0.7; when Ln=Gd, x=0.5.With the lanthanide cation diameter increment, the solid solubility limit of related system gradually reduced till reaching the only value.In BaO-Ln₂O₃-TiO₂ system, when the lanthanide concentration was determined, with the Ln3+ ion diameter increased, the crystal cell would mainly expand at AB plane that was vertical to C axis, so the change of crystal cell parameters were mainly represented as the increment of a and b, but the change of c was quite few. When the concentration of lanthanide ion increased, the whole crystal cell would shrink. Besides, the decrease of lanthanide cation diameter of Ba_6-3xLn_8+2xTi₁₈O₅₄ solid solution will increase the lean angle of [TiO6] octahedral, while the lean angle increase would also lead to the crystal cell volume shrink.The effect of lanthanide ion diameter, ion content, electronegativity and polarizability to dielectric constant were researched in this thesis. The tungsten-bronze type like structure caused high permittivity of BaO-Ln₂O₃-TiO₂ system, while the exsistence of lanthanide ion resulted in the permittivity change in extent. With the raw material recipe Ba_6-3xLn_8+2xTi₁₈O₅₄, with lanthanide ion diameter, polarizability and electronegativity increased, the dielectric constant showed a increasing trend. When x=2/3,the quality factor of BaO-Ln₂O₃-TiO₂ was the maximum. With the decrease of ion diameter and Ln3+ electronegativity, the maximum quality factor would increase accordingly.The lanthanide ion concentration increment , Ln3+ ion diameter decrease and structure torlerance factor decrease were advantaged to obtain near-zero resonant frequency temperature coefficient.The cell parameter and microwave dielectric properties of BaO-Sm2O3-Nd2O3-TiO2 and BaO-Nd2O3-TiO2 doped by Bi2O3 identify the rule as before. BaO-CeO2-TiO2 microwave dielectric ceramic was the special case in BaO-Ln₂O₃-TiO₂ seriers just because the smaller ion diameter and unstable valence. The sintering character and phase composition were different from other.And the permittivity and quality factor were lower than those of other BaO-Ln₂O₃-TiO₂ ceramics.更多还原