【作者】 熊钢；

【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】 本文在调研分析了国内外微波介质陶瓷研究状况的基础上,对Ca(Li_1/3Nb_2/3)O_3-δ基陶瓷的组成、微观结构和介电性能及相互间关系等进行了系统的研究。探讨了介电常数、介电损耗和谐振频率温度系数的主要影响机制,对控制介电常数、降低介电损耗以及调节谐振频率温度系数提出了可行的改性方法及相关改性机理。不掺杂Ca(Li_1/3Nb_2/3)O_3-δ陶瓷为典型的氧缺位型、钙钛矿结构的多元氧化物材料,随着B位Zr⁴⁺取代量的增加,逐渐转化为氧过剩型。研究了Zr⁴⁺置换对Ca[(Li_1/3Nb_2/3)_1-xZr_3x]O_3-δ（0.0≤x≤0.1）系陶瓷的晶胞参数、容忍因子、B位l:2有序度、离子极化率等方面的影响,以及晶体结构与介电性能之间的关系,以加深对微波介电性能的影响机理的认识。Zr⁴⁺离子取代(Li_1/3Nb_2/3)^3.67+复合离子,增大了Ca[(Li_1/3Nb_2/3)_1-xZr_3x]O_3-δ陶瓷体系的离子理论极化率。但随体系介电常数εr提高,B位l:2有序度减小,Qf值下降。Zr取代使体系的频率温度系数τf有所改善,例如x=2mol%时为-16.3 ppm/℃,x=10mol%时为-7.3ppm/℃。研究了Zr、Ti复合置换对Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15-xTi_x]O₍^3+δ陶瓷的结构及性能的影响。Ti⁴⁺进入体系B位导致体系介电常数增大,Qf值由x=0mol%时的13100 GHz增加到x=10mol%时的16570GHz,然后又减少到x=15mol%时的16020GHz。其原因是Zr⁴⁺取代Li+产生的多余电子会导致陶瓷电阻率的降低,增加了电导损耗,而Ti⁴⁺取代Nb5+产生空穴,于是电子浓度下降,电导损耗减小;但Ti⁴⁺取代量增加到一定程度时,由于空穴浓度的上升,导致电导损耗又开始增大。随Ti含量的增加,τf向负谐振频率温度系数方向增大。同时研究了制备工艺对Ca(Li_1/3Nb_2/3)O_3-δ基陶瓷介电性能的影响。研究了Ba²⁺、Sr²⁺及Nd³⁺置换Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O₍^3+δ体系A位Ca²⁺对晶体结及介电性能的影响,探讨了(Ca_1-xBa_x)[(Li_1/3Nb_2/3)_0.95Zr_0.15]O₍^3+δ （0.0≤x≤0.2）、（Ca1-xSrx） [(Li_1/3Nb_2/3)_0.95Zr_0.15]O₍^3+δ（0.0≤x≤0.2）及(Ca_1-xNd_x) [(Li_1/3Nb_2/3)_0.95Zr_0.15]O₍^3+δ （0.0≤x≤0.2）体系中晶体结构与介电性能之间的关系。适量Ba²⁺、Sr²⁺置换Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]³⁺δ陶瓷A位Ca²⁺,钙钛矿结构B位键价减小,τf向正谐振频率温度系数方向增大,材料性能得到改善。当x=2.5mol%时,含Ba体系有很好的介电性能:εr=34.3,Qf =13400GHz,τf = 2.1 ppm/oC;而含Sr体系则在x=5mol%时介电性能最佳,其εr=32.5,Qf =13500GHz,τf = -2.4 ppm/oC。Nd³⁺置换的体系中,适量置换,l:2有序度提高,陶瓷品质因素因而大幅度提高;过量置换会降低体系的1:2有序度。采用Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O^_3+δ作为原始组分,以ZnO-B₂O₃-SiO₂ （ZBS）、ZnO-B₂O₃-Na₂O （ZBN）、B₂O₃作为烧结助剂降低陶瓷的烧结温度,研究单一或复合掺杂这些助剂后该陶瓷体系的烧结特性、结构及微波介电性能,探讨了Ca(Li_1/3Nb_2/3)O_3-δ基陶瓷低温烧结机理。研究表明,单一掺杂时,ZBS、ZBN及B₂O₃均能降低陶瓷的烧结温度, ZBS的助烧作用有限,掺入量为7wt%时,于1000℃烧结,样品的微波介电性能为:εr=31.1,Qf=9530 GHz,τf = ?8.9 ppm/℃;B₂O₃的助烧效果最好,掺入1.0wt% B₂O₃,在990℃烧结4小时,陶瓷微波介电性能最佳:εr=33.1, Qf =13700GHz,τf =-6.8ppm/℃。而且,掺入2.0wt% B₂O₃,在940℃烧结,Qf可达8700GHz。复合掺杂比单一掺杂能更有效降低陶瓷的烧结温度,Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O^_3+δ +3.0 wt%ZBN +2.0wt% B₂O₃陶瓷在950℃烧结,有着较好介电性能,其εr=31.2 , Qf=10530GHz,τf =-5.1ppm/℃。研究了Zr⁴⁺电荷、结构非平衡取代Ca(Li_1/3Nb_2/3)O_3-δ陶瓷B位(Li_1/3Nb_2/3)^3.67+对原缺陷模型的影响,研究表明,随氧分压及杂质浓度的增加,锂空位浓度不断提高,氧空位浓度不断下降,氧缺位型Ca(Li_1/3Nb_2/3)O_3-δ化合物转变为氧过剩型化合物。同时研究了B位Zr、Ti复合置换的Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15-xTi_x]O^_3+δ （0.0≤x≤0.15）陶瓷及A位Nd置换的(Ca_1-xNd_x)[(Li_1/3Nb_2/3)_0.95Zr_0.15]O^_3+δ（0.0≤x≤0.20）陶瓷的缺陷化学,研究表明,随杂质Ti⁴⁺浓度的增加,电子浓度不断下降,空穴浓度不断提高;而A位Nd置换使晶体中参与电导的电子浓度上升。探讨了点缺陷电子电导对微波介质陶瓷介电损耗的影响机理。更多还原

【Abstract】 On the basis of research and analysis on a number of both domestic and foreign studies on microwave dielectric ceramics, this paper has systematically investigated the composition, microstructure, and dielectrics properties of Ca(Li_1/3Nb_2/3)O_3-δ ceramics, and their mutual relationship. Discussion is made on the principal influence mechanism of dielectric constant, dielectric loss, resonance frequency temperature coefficient. Feasible modification method and related mechanism is proposed for dielectric constant control, dielectric loss reducing, and resonance frequency temperature coefficient adjustment. Un-doped Ca(Li_1/3Nb_2/3)O_3-δ ceramics is of typical oxygen vacancy- type perovskite structure oxide, with the increase of B site Zr⁴⁺ substitution, it was transformed gradually into over the oxidized type.The influence of B site Zr⁴⁺ substitution on the lattice parameter, the tolerance factor, the degree of B-site 1:2 ordering and the ionic polarizability and the relationship between the crystal structure and dielectric properties of Ca (Li_1/3Nb_2/3)_1-xZr_3x]O_3-δ （0.0≤x≤0.1） ceramics was investigated. A increase of the ionic polarizability in Ca[(Li_1/3Nb_2/3) 1-xZr3x]O_3-δ ceramics caused by B site Zr⁴⁺ substitution.Therefore, theεr value of specimens increased, but the degree of B-site 1:2 ordering and the Qf value decreased. Theτf value increased from ?16.3 to ?7.3 ppm /oC with increasing Zr ⁴⁺content from 2.0 to 10.0mol%. The influence of multiple substitution of Zr⁴⁺ and Ti⁴⁺ on the ceramic structure and dielectric properties of Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15-xTi_x]O_³⁺δ （0.0≤x≤0.15）ceramics was studied. The substitution of Ti⁴⁺ at B site caused the increase of dielectric constant is increased. At first the Qf value is increased from 13100 GHz to 16570GHz as Ti⁴⁺ content increased from 0 to 10mol%, then it is decreased to 16020GHz at Ti⁴⁺ content of 15mol%. The reason is the substitution of Zr⁴⁺ to Li+ at B-site generated redundant electronic, lowered the resistance of ceramics, and leaded to an increase of conductivity loss, while the substitution of Ti⁴⁺ to Nb5+ generated hole, the electronic concentration was decreased, and conductivity loss decreases, but with increasing Ti⁴⁺ content to a certain degree, conductivity loss increased again due to the hole concentration increased. With a increase of Ti⁴⁺ content , theτf value moved to the negative direction. At the same time, effect of preparation processing on dielectric properties of Ca(Li_1/3Nb_2/3)O_3-δ-based ceramics was discussed.The effect of A site Ba²⁺, Sr²⁺ and Nd³⁺ substitution on the crystal structure and dielectric properties of Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O_³⁺δ ceramics was investigated. The proper substitution of Ba²⁺ and Sr²⁺ can improve the temperature coefficient of Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O_³⁺δ system, which was resulted from the decrease of the B-site bond valence of the ABO3 perovskite structure. At x=2.5mol%, good dielectric properties were obtained in (Ca_1-xBa_x)[(Li_1/3Nb_2/3)_0.95Zr_0.15]O_³⁺δ （0.0≤x≤0.2） ceramics:εr=34.3, Qf =13400Ghz andτf = 2.1 ppm/oC; the dielectric properties wereεr=32.5, Qf =13500GHz andτf = -2.4 ppm/oC for (Ca_1-xSr_x) [(Li_1/3Nb_2/3)_0.95Zr_0.15]O_³⁺δ （x=5mol%）. The proper substitution of Nd³⁺ can enhanced the degree of B-site 1:2 ordering. The Qf value of the specimens increased rapidly. Excessive substitution made the degree of B-site 1:2 ordering.Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O_³⁺δ ceramics were selected as the research objects, and ZnO-B₂O₃-SiO2 （ZBS）, ZnO-B₂O₃-Na2O （ZBN） and B₂O₃ were regarded as sintering aids. The effect of single aid or multiple aids on the sintering behavior, microstructure and dielectric properties of Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O_³⁺δ ceramics was discussed, and the low temperature sintering mechanism was revealed. The results of research show that ZBS, ZBN and B₂O₃ can also lower the sintering temperature. The effect of B₂O₃ aid was best. When the B₂O₃ of l.0wt% were added, the optimum microwave dielectric properties:εr =33.1,Qf =13700GHz andτf =- 6.8×10^-6/℃were obtained at the sintering temperature of 990oC. Furthermore. The specimens with 2.0wt% B₂O₃ sintered at 940oC for 4h showed good microwave dielectric properties ofεr=31.4 ,Qf =8700GHz andτf = - 5.2×10^-6/℃. Multiple aids can reduced the sintering temperature more effectively. Sintered at 950℃, the dielectric properties of Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15]O_³⁺δ with 3.0wt%ZBN +2.0wt% B₂O₃ wereε_r=31.2, Qf=10530Ghz andτ_f = ?5.1ppm/℃.The influence of electric charge and structure unbalance substitution of Zr⁴⁺ at B site on the original defect model in Ca(Li_1/3Nb_2/3)O_3-δ ceramics was studied. The result shows that the electron concentration rises with a increase of the partial pressure of oxygen and dopants concentration, the oxygen vacancy concentration decreased, and Ca(Li_1/3Nb_2/3) O_3-δ compounds changed from oxygen vacancy-type into oxygen ionic Surplus-type compounds. At the same time, the defect chemistry of Ca[(Li_1/3Nb_2/3)_0.95Zr_0.15-xTi_x]O_3+δ （0.0≤x≤0.15） ceramics was discussed. The study shows that the decrease of electron concentration with a increase of Ti⁴⁺ content, and the increase of electron concentration with increasing Nd³⁺ content. The influence mechanism of point defect electronic conductivity on the dielectric loss of microwave dielectric ceramics was discussed.更多还原