【作者】 王静；

【导师】 姜胜林；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2013， 博士

【摘要】 随着电子信息技术的高速发展，电子产品不断向轻、薄、短、小等方向迈进，作为基础电子元件的陶瓷叠层电容器（MLCC）也向微型化、大容量、高比容、高电压、高频率、抗干扰、多功能和低功耗等方向发展。近年来，随着MLCC向高温应用领域的不断拓展，高介高稳定性MLCC的研究成为当务之急。钛酸钡基铁电陶瓷具有较高的介电常数，适当的居里温度，通过掺杂可以调整居里点和介电常数，是制造高介高稳定性MLCC的重要材料之一。针对现有钛酸钡基陶瓷材料温度稳定性差的问题，论文在分析传统固相法非化学均匀性掺杂制备芯/壳结构陶瓷的基础上，设计了粉体成分的多层次结构，提出了常压液相技术和分步式生长技术相结合制备芯/壳陶瓷粉体的合成路线。按照Lichtenecher对数叠加原理及介电多峰叠加效应，具有不同居里温度的介质层进行包覆生长后，陶瓷材料介电常数呈现多峰效应，介温特性得到改善。与传统方法不同，分步式液相法制备的芯部和壳部均为铁电相，材料整体的介电常数通过适当的掺杂可大幅度提高。通过实验得到了最佳合成条件：反应时间为3h，反应物浓度为0.2mol/L，介质的[OH-]为_0.5 mol/L，芯/壳结构粉体的粒径为300nm，均匀分散。芯/壳结构晶粒的芯部和壳部对陶瓷的介电性能有着重要的影响。论文首先对芯部材料进行了对比选择，分别以居里点较高的(Bi_0.5Na_0.5)TiO₃和(Ba_0.985Bi0.01)TiO₃纳米晶作为晶粒芯部，以居里点较低的BaTi_0.9Zr0.1O₃作为壳部，制备出两个系列的陶瓷电容器。实验结果表明，(Bi_0.5Na_0.5)TiO₃-BaTi_0.9Zr0.1O₃陶瓷中的(Bi_0.5Na_0.5)TiO₃可明显提高陶瓷材料的居里温度，但是由于(Bi_0.5Na_0.5)TiO₃的介电常数过低导致材料整体的介电常数不高，仅为2000；Ba_0.985Bi0.01TiO₃-BaTi_0.9Zr0.1O₃陶瓷的介电常数、温度稳定性均优于单相材料，最高介电常数接近6000，在-55℃、130℃和160℃的介电常数温度变化率分别为-12.0%、14.1%和-8.3%，满足X8R的温度特性，且介电损耗小于0.1。总结了液相法制备的陶瓷材料性能优异的原因与铁电相比例密切相关。基于Ba_0.985Bi0.01TiO₃-BaTi_0.9Zr0.1O₃体系表现出的优越介温特性，论文讨论了不同保温条件下Zr含量对该体系的微观结构和介电特性的影响。结果表明，在保温时间为1h的烧结条件下，随着Zr含量的增多，陶瓷的介电常数逐渐下降，居里点持续向低温移动，材料的温度稳定性不断增强，当x=0.1时，材料的稳定性满足X8R的特性要求；在保温时间为2h的烧结条件下，陶瓷材料的化学均匀性得到了较大程度的提高，当x=0.001时，介电常数峰值为55,678，介电损耗为0.1，在20¹40℃范围内的温度变化率低于21%。为了研究壳层对性能的影响，论文对Ba_0.985Bi0.01TiO₃-BaTi_1-xSnxO₃体系进行了系统研究，讨论了Sn的掺杂量和烧结工艺对物相和介电性能的影响。实验发现，随着Sn添加量的增大，样品的介电常数峰值先提高再降低，稳定性也先增强再减弱，当x=0.02时，在-55℃、120℃和170℃时的容温变化率分别为-15%、14.4%和-15%，温度稳定性满足X8R的要求，介电损耗低于_0.5，介电常数接近25,000；两步烧结法展现出了抑制晶粒生长、提高介电常数、增强稳定性和降低介电损耗的优势，材料的介电常数高于22,000，介电损耗低于0.6，在40¹40℃范围内的介温变化率低于10%。基于稀土元素可显著改善钛酸钡介电性能的原理，本论文对Ba_0.985Bi0.01TiO₃-Ba_1-1.5xLaxTiO₃体系进行了研究。讨论了La的掺杂量、MgO的添加以及烧结温度对物相和介电性能的影响。结果显示，当La的添加量为0.01时，材料的介电常数最大且介温稳定性最好，介电常数达到6000以上，介电损耗低于0.35，相对于30℃介温变化为-15%¹0%；MgO的添加降低了陶瓷的烧结温度，减小了陶瓷的损耗并促进了陶瓷晶粒的生长，但温度稳定性变差；Bi2O₃在烧结过程中的挥发和凝聚导致不同温度下成瓷的样品的微观形貌和密度迥然不同，由此也影响了材料的介电常数和介电损耗。随着成瓷温度的升高，各样品的介电常数峰值和介电损耗经历了先减小再增大又减小的变化，在1250℃和1270℃成瓷的样品符合X8R的温度特性，在-55℃、110℃和150℃时的容温变化率分别为-5.2%、13.8%和-12.8%，介电常数峰值接近9,500，介电损耗低于0.27。更多还原

【Abstract】 With the rapid development of electronic information technology, electronic productsare getting lighter, thinner, shorter and smaller. Multilayer ceramic capacitor （MLCC） as abasic electronic components subsequently are developing for miniaturization, large capacity,high volume, high voltage, high frequency, anti-jamming, multi-function and low powerconsumption. In recent years, with the working temperature of MLCC has become higherand higher, research on permittivity and temperature-stability of MLCC has becomeimperative. Barium titan ate ceramic has high dielectric constant, proper Curie temperature（Tc）, and adjustability in permittivity and Tc by doping, so it is the best material tomanufacture ceramic capacitors with high permittivity and stability.In order to improve the temperature stability of the capacitor materials, this paperproposed the synthesis route of multilayer structure grain using the atmospheric liquidphase technology and hierarchical classification growth technologies, based on thetraditional core/shell structure prepared by solid-phase method. Every dielectric layer in thegrain had different Curie temperature. When the grain grew layer by layer, its performancewould be the stack results of all the dielectric layers according to the Lichtenecher’s lawand multimodal effect. Distinct from traditional method, each dielectric layer in themultilayer structure was ferroelectric phase, so the dielectric constant could be increasedgreatly through proper doping. Through experimental studies, the optimum conditions forthe synthesis was as followed: the reaction time of3h, reactant concentration of0.2mol/Land [OH-] of_0.5 mol/L. The particle size is about300nm after surface-coating.Core and shell both have important influence on the properties. In order to study theeffects of core in this method, the article chose materials with high Tc by comparing(Bi_0.5Na_0.5)TiO₃and (Ba_0.985Bi0.01)TiO₃as grain cores respectively, BaTi_0.9Zr0.1O₃as shellwith low Tc growing on the surface of both grain cores. The results showed that(Bi_0.5Na_0.5)TiO₃obviously improved the Curie temperature. But the low dielectric constantof (Bi_0.5Na_0.5)TiO₃led to poor properties of the material. However, the dielectric constantand temperature stability of Ba_0.985Bi0.01TiO₃-BaTi_0.9Zr0.1O₃ceramic were superior to thatof single phase materials. Its highest dielectric constant was close to6,000, temperaturecoefficients of capacity were12.0%,14.1%and8.3%at-55oC,130oC and160oC, respectively, which met X8R specification, dielectric loss was less than0.1. It wassuggested that the nice properties of powders prepared by liquid-phase method wereattributed to the ferroelectric phase.Based on the stability of Ba_0.985Bi0.01TiO₃-BaTi_1-xZrxO₃ceramics, the microstructureand dielectric properties of Ba_0.985Bi0.01TiO₃-BaTi_1-xZrxO₃ceramics sintered at two differentconditions were studied. When holding time was1h, with the increase of Zr content,dielectric constant declined, Curie point moved to lower temperature, and the temperaturestability was improved. When x=0.1, temperature coefficients of capacity met X8Rspecification. When holding time is2h, ceramic materials with chemical uniformity wereobtained. When x=0.001, the material had high permittivity of55,678, the temperaturecoefficient of capacity was less than21%in the temperature range of20¹40oC, and themaximun dielectric loss was less than0.1.In order to research the effcts of shell on the material properties, Ba_0.985Bi0.01TiO₃-BaTi_1-xSnxO₃ceramic materials with core/shell structure were prepared. The influences ofSn content and sintering condition on phase constitution and dielectric properties werediscussed. With the amount of Sn increased, the peak value of permittivity increased beforedropping, as well as temperature stability. When x=0.02, the temperature coefficients ofcapacity were-15%,14.4%and15%at-55oC,120oC and170oC, respectively, which wasclose to X9R specification, and the dielectric loss was less than_0.5. Two-step sinteringmethod can inhibit grain growth effectively. Samples sintered by this method had a highpermittivity above22000and a falling dielectric loss, less than0.6. Its temperaturecoefficient of capacity was less than10%in the range of40¹40oC.Due to the obvious effects of rare earth element on dielectric performance of bariumtitanate, Ba_0.985Bi0.01TiO₃-Ba_1-1.5xLaxTiO₃ceramic powders with core/shell structure wereprepared. The influences of La content, addition of MgO and sintering temperature on thephase constitution and dielectric properties were discussed. When La content is0.010,dielectric constant and temperature stability were the most outstanding. Permittivity washigher than6000, dielectric loss was less than0.35, and the temperature coefficient ofcapacity was in the range of-15%¹0%. Due to the existence of MgO, grains grewsufficiently and could complete densification in low temperature. Dielectric loss at roomtemperature was significantly lowered. Due to evaporation and agglomeration of Bi2O₃in sintering process, samples sintered in different temperatures were very different from eachother in microstructure and density. The permittivity and dielectric loss were alsoinfluenced. The maximum dielectric constant decreases first, and then increases beforedropping again, mimicking the change of dielectric loss. Samples sintered at1250oC and1270oC had the best temperature stability, which meet X8R requirements. Thepermittiveity was near to9500, dielectric loss was less than0.27, and the temperaturecoefficient of capacity was in the range of-12.8%¹3.8%.更多还原