【作者】 王伟；

【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， 2005， 博士

【摘要】 Ba(Mg_1/3Ta_2/3)O₃ （BMT）陶瓷是中低εr类微波介质陶瓷材料中最优秀的典型代表,也是目前卫星通讯等高频领域所用的主要介质材料,因而成为当前国际上微波介质陶瓷研究与应用领域的热点之一。本论文工作从材料的微观结构出发,分析探讨BMT陶瓷介电损耗与谐振频率温度系数（τ_f）的内在机制与影响因素,以此为基础通过掺杂纳米添加剂对BMT系统介质陶瓷进行改性研究,主要研究目的是希望获得同时具有良好烧结性能与优异微波介电性能的BMT系统微波介质材料。1.对BMT陶瓷介电性能的理论研究进行了总结分析:材料在微波频率下的介电损耗分为内部损耗与外部损耗,内部损耗取决于材料的化学结构组成与晶体结构,外部损耗主要取决于材料的显微结构;材料的介电常数温度系数（τ_ε）不仅与材料的化学组成有关,还会受到材料晶体结构的影响,其原因在于晶体结构的改变直接影响到材料微观极化率的温度依赖性。2.使用多种金属离子以传统电子陶瓷工艺对BMT陶瓷进行掺杂改性,通过经典谐振子模型建立材料的离子物性参数与极性晶格振动模的联系,探讨分析了不同位置取代离子对材料性能的作用影响及规律:BMT系统的ε_r与τ_f主要取决于材料的低频区极性晶格振动模的特性变化,系统的内部损耗则取决于所有极性晶格声子的非谐效应,通过掺杂取代可调整原BMT体系极性晶格振动模的特性,进而改善材料的微波介电性能。3.将Sn⁴⁺与Mn²⁺分别以纳米粉体和溶液的形式对BMT系统陶瓷进行掺杂改性,获得了具有良好烧结性能与优异微波介电性能的BMT-BS系微波介质陶瓷材料:掺杂1.5 mol%Mn的0.85BMT-0.15BS系统在1450℃保温4h后的τf近似为0ppm℃^-1,体密度达到7.33g/cm³,εr为24.9, Q×f值为1.85×10⁵GHz。4.采用液相包覆—界面反应的方法在800℃下经济高效地合成出成份均匀、纯度较高、具有良好烧结活性的BMT纳米粉体,通过均匀设计与多重线性回归对以纳米BMT粉体作为添加剂改善BMT体系烧结性能的研究进行了优化分析,在1550℃下保温4h的含8.5wt%添加剂的BMT样品的相对密度达到93.80%,微波介电性能为:ε_r=24.8;τ_f=6ppm℃^-1;Q×f= 1 .24×10⁵GHz。更多还原

【Abstract】 As the most outstanding representative of moderate ε_r microwave dielectricceramics and main materials used currently at high-frequency regions such as satellitecommunication systems etc, Ba(Mg_1/3Ta_2/3)O₃ （BMT） compounds have gotten closeattention in the field of microwave ceramics. In this dissertation, the mechanisms ofdielectric loss and temperature coefficient of resonant frequency （ τ_f） wereinvestigated from microscopic material parameters and, based on such mechanismsanalysis, the studies on modified BMT systems were conducted by using nanoscaledpowders additives. The goal of this work is to obtain novel modified BMT materialswith both good sinterability and excellent microwave dielectric properties.1. The theoretical studies on dielectric properties of BMT ceramics were analyzedand summarized: the dielectric loss can be classified as intrinsic loss and extrinsicloss, the former is determined by chemical composition and crystal structure, thelatter is closely related to material microstructure;temperature coefficient ofdielectric constant （ τ_ε） is found to be not only related with material composition,but also with crystal structure, which directly influences the temperaturedependence of material microscopic polarizabilities.2. A systematically study on modified BMT systems were conduced by dopingvarious metallic ions through conventional electronic ceramics technology. Theions parameters were correlated with material polar lattice vibrations throughclassical oscillator model, and the relation between materials properties and ionscharacteristics at different substituting sites were also investigated: dielectricconstant （ ε_r） and τ_f are mainly determined by polar phonons characteristics atlow frequency regions;the intrinsic loss is determined by anharmonic effects ofall polar phonons;doping different ions at different sites can lead to the changesof lattice phonons characteristics, thus improving dielectric properties.3. A new modified BMT system ceramics with both good sinterability and excellentmicrowave properties were prepared by doping Sn4+and Mn²⁺ in the form ofBaSO₃ （BS） nanoscaled powders and Mn²⁺ solutions, respectively. After dopedwith 1.5mol% Mn, the 0.85BMT-0.15BS system can be sintered at 1450℃ for 4h.The as-prepared sample shows a density of 7.33g/cm³;τ f≈0ppm℃^-1;ε_r=24.9;Q× f= 1.85×10⁵GHz.4. BMT nanoscaled powders with high purity and good sintering activity wereeconomically synthesized at 800℃ through liquid-phase coating interfacialreaction and then were used as additives to improve the sinterability of BMTsystem. Uniform experimental design and multiple linear regressions were appliedto optimize the formula and preparation technology. When additive content is8.5wt%, the BMT materials sintered at 1550℃ for 4h show about 93.8% of thetheoretical density and good microwave dielectric properties: ε r=24.8;τ f=6ppm℃-1;Q× f= 1 .24× 105GHz.更多还原