【作者】 张奇；

【导师】 袁松柳；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2009， 硕士

【摘要】 随着微电子器件的尺寸不断的减小,高介电常数材料在微电子器件中,尤其是在动态随机存储器的应用中,扮演着越来越重要的角色。近年来一种很特殊的钙钛矿结构的材料CaCu₃Ti₄O₁₂由于具有高介电常数而引起了研究人员的关注。它的介电损耗比较低,介电常数却很高,温度稳定性非常好,在l00K⁴00K甚至更广的温度范围内介电常数保持稳定。目前就CaCu₃Ti₄O₁₂巨介电常数的起因还没有一致的观点,大多数学者支持内部阻挡层电容器模型（Internal Barriers Layer Capacitance,IBLC）,但存在着很多争议。本文通过磁性离子替代钛位的研究,初步的讨论了巨介电常数起因,认为介电性起源于二个区域:晶粒,晶界。在某些体系中还观察到了类铁电性,主要是起源于晶粒内部自发极化以及Maxwell-Wagner极化。主要内容如下:第一章介绍了巨介电材料的研究概况和应用前景,简要描述了CaCu₃Ti₄O₁₂的晶体结构,巨介电性,以及巨介电性的可能起因（IBLC）,并对目前掺杂体系作了简单介绍,最后是给了出了本文的选题依据。第二章主要从材料制备上介绍了样品的制备工艺,主要使用了特殊的溶胶-凝胶法Peckin法制备了本文中的样品。第三章从实验上研究了三类磁性掺杂体系（Co,Ni,Mn）的结构及其介电性,类铁电行为,及可能存在的磁性。基于实验结果,讨论了样品的介电,铁电的起因。得出如下结论:（1）对于掺Co体系,介电性能得到了很大程度的提高,从Cole-Cole图谱上看,观察到了三类响应。介电响应主要起因于三个区域:低频区20¹04Hz主要由晶界引起的;中频区104¹06Hz有一平坦的响应区,主要来源于肖特基势垒;高频区106¹08Hz起源于晶粒内部。这三个区域的响应随着掺杂量的升高分别有不同的变化:低频段和高频段响应不断变强,而中频段响应慢慢消失。该体系并未观察到类铁电行为。（2）对于掺Ni系列样品,介电性有所增强。从Cole-Cole图上看,主要是由晶界和晶粒引起的,晶粒内部响应移向了低频区。在该体系中观察到了弛豫铁电性。随着x的增大,铁电性先增强后减弱。主要是由晶粒的自发极化引起的和表面极化造成的。我们还研究了尺寸效应,烧结温度越高,介电性越强,但类铁行为消失。（3）对于掺Mn体系,介电性急剧下降,晶粒电阻增大,导致内部阻挡层结构特征变弱,甚至消失。在整个可观测频率范围内,阻抗谱中只存在晶界响应。晶粒响应移向了高频段,也有可能消失。样品的烧结温度越高,介电常数越小。在该体系中我们观察到了类铁电行为,相比于CaCu₃Ti₄O₁₂有所减弱,属于弛豫类铁电行为。烧结温度越高类铁电性越强。在以上三种体系中我们并未观察到相关磁性。第四章主要研究了LCMO/CaCu₃Ti₄O₁₂复合样品的磁电阻行为,通过在LCMO的颗粒边界引入顺磁性第二相CaCu₃Ti₄O₁₂相,发现磁电阻效应得到了大大的提高。在3T的外场下,复合量为10%的样品磁电阻达到了73.4%,主要是由非本征效应引起的磁电阻效应。TP会随着复合量的增高而向低温区移动,同时在x=0.03,.0.05,0.10样品中观察到了热滞行为。这与CaCu₃Ti₄O₁₂的弛豫性质及边界上的自旋无序有一定的联系。更多还原

【Abstract】 With the size of micro-electronics device getting smaller, high dielectric constant material is playing more and more important role in it, especially in the application of dynamic random access memory. Recently, researchers pay close attention to a special kind of material, CaCu₃Ti₄O₁₂ ceramic, which has giant dielectric constant,and low loss tangent, good temperature stability. Its dielectrics constant nearly does not change in a big temperature range such as100K to 400K. At present, there are many different perspectives about the origin of giant dielectric constant. Most of researchers hold on the ideal of Internal Barriers Layer Capacitance, which was disputed by others.In this thesis, we substitute Ti ion for magnetic ion, and study its influence of the dielectric property. We think that dielectric property origin from two regions in its microstructures: the interior of crystal grain, crystal grain boundary. Some of samples, we observe ferroelectric-like property, mainly originated from interface polarization and crystal spontaneous polarization in some system. The main contents of the thesis are as follows:In chapter one, the study background and application perspectives of giant dielectric material are introduced, and briefly describe the crystal structure of CaCu₃Ti₄O₁₂. Also we show the main property of it, and the possible origin （IBLC）. The doped systems are reviewed to the point .The study basis of this research is finally offered.In chapter two, the preparation procession of the samples in our experiment are introduced. We prepare the sample by special sol-gel method.In chapter three, we study experimentally their dielectric, ferroelectric-like properties in the doped sample. Basic on the result of the experiment, the following conclusions are reached:（1） For the samples doped by Co ion, the dielectric constant increases sharply more than CaCu₃Ti₄O₁₂’s. From Cole-Cole circle, we find three kinds of response. The dielectric response result from three regions: low frequency responses by crystal boundary （about20¹04Hz）, middle frequency （104¹05Hz） in which exist a planar responses by Schottky barriers, high frequency responses by the crystal interior. There are different changes by the amount of the adulteration in the three regions:The low and high frequency response gets stronger with the increase of the adulteration, while the low frequency response gets smaller, even die away with the higher adulteration. In this doping system, no ferroelectric phenomenon is observed. （2） In the sample doped by magnetic Ni ion, the dielectric constant enhances slowly, compared with Co doping system. From Cole-Cole circle, we know the dielectric contribution is mainly from crystal grain boundary and grain , the grain response moves to lower frequency region, which we can not measure the characteristic frequency. In them, we observe relax ferroelectric phenomenon and the ferroelectric property is stronger than the sample with no dopant in x=0.08, but then get small with the larger x, which maybe exist the second phase. The origin of relaxor ferroelectric is mainly from spontaneous polarization in crystal. We also study the particle size effect by different sintering temperature, the higher temperature, the higher dielectric constant with no ferroelectric, which is relaxor’s character.（3） For the dopant Mn, the dielectric constant decrease sharply. The crystal grain resistance gets larger in the result of the miss of the structure of Internal Barriers Layer. In Cole-Cole circle, we observe grain boundary response without the grain and interior response that maybe move to higher frequency region or vanish. The higher sintering temperature, the smaller dielectric constant. In this doping system, we observe relax ferroelectric, which decrease the ferroelectric compared with no doping system. We find the ferroelectric gets stronger with the higher sintering temperature, but is still relaxor ferroelectric. There is no magnetic property of three series samples found.In chapter four, we mainly study the magneto resistance of the Composite System of LCMO/ CaCu₃Ti₄O₁₂by introduction of the second phase of paramagnetic CaCu₃Ti₄O₁₂ to LCMO crystal grain boundary. We find the magneto resistance enhance very much. Under 3 T field, the magneto resistance increases to a maximum value of 73.4% for x = 0.1 composite. The enhancement of magneto resistance results from extrinsic effect. Transition temperature TP moves to the lower temperature region with the higher composite. Simultaneously, the thermal hysteresis behavior in resistively is observed in x =0.03, x =0.05 and x = 0.1 samples, respectively. The MR enhancement and the abnormal induced by the interaction product layer between LCMO and CCTO.更多还原