【作者】 俞鹏飞；

【导师】 崔斌；

【作者基本信息】 西北大学 ， 无机化学， 2007， 硕士

【摘要】 BaTiO₃具有钙钛矿结构，由于其特殊的介电、压电、电致伸缩、电光性质以及相应的电子学应用备受关注，主要用作多层陶瓷电容器（MLCC）的基质材料。BaTiO₃纳米粉体的制备方法一直是人们的研究热点。溶胶-凝胶法所得粉体纯度高、粒径小、均匀性好，在实际操作中的应用更为广泛。但其制备的钛酸钡纳米粉体很容易形成团聚，所以本论文采用不饱和有机酸、一元和二元有机酸辅助溶胶-凝胶法制备了分散性较好的BaTiO₃纳米粉体及其具有良好介电性能的陶瓷，用油酸作表面活性剂合成了单分散纳米Ni、Ag和Fe₃O₄纳米粒子，并进一步制备了纳米银掺杂的高介电常数BaTiO₃陶瓷。此外，在本课题组原有的X7R瓷料基础上，进一步制备出了银掺杂的高介电常数的X7R型BaTiO₃基瓷料。1、用不饱和长链脂肪酸（油酸）作表面活性剂辅助溶胶-凝胶法制备了BaTiO₃纳米粉体，粒径范围为22到55nm。随着[Ti（OBu）₄]／[OA]比从1∶1到4∶1，所得粉体分散性降低。[Ti（OBu）₄]／[OA]比为1∶1，900℃／2h预烧、1250℃／2h烧结得到的BaTiO₃陶瓷其相对密度达到98.5％，室温介电常数达4569，介电损耗为0.027。2、用五种一元长链有机酸作表面活性剂辅助溶胶-凝胶法制备了BaTiO₃纳米粉体，粉体粒径范围为20到55nm。随着碳链的增长，粉体的粒径先减小后增大。除硬脂酸作表面活性剂制备的陶瓷外，随着碳链的增长，陶瓷的晶粒尺寸和相对密度都随之增大。月桂酸作表面活性剂制备的BaTiO₃粉体粒径最小，分散性最好且粒子形状趋向于球形，用其制备的陶瓷晶粒均匀且具有合适的晶粒尺寸（1.05μm），室温介电常数高达4319，介电损耗为0.022。3、用己二酸和癸二酸作表面活性剂辅助溶胶-凝胶法制备了BaTiO₃纳米粉体，粒径范围为60到65nm。癸二酸作表面活性剂制备的BaTiO₃陶瓷室温介电常数达3270，相对密度为97.1％。与一元酸相比，随着羧基数目的增加，BaTiO₃粉体的原始粒径明显增大，并且所制得的陶瓷的晶粒尺寸和相对密度也增大。而随着二元酸链长的增加，粉体粒径也增加，所得陶瓷的晶粒尺寸略有减少但相对密度增大。此外，与不饱和有机酸油酸相比，二元有机酸作表面活性剂制备的粉体粒径明显较大，故所得陶瓷相对密度较小。较大的粉体原始粒径是由于二元酸有两个羧基与钛酸钡前驱体键合牢固，“微胶囊”更稳定，能够容纳更多的钛酸钡前驱体，预烧后得到较大的晶粒。原始晶粒越大，团聚体也越大。4、通过溶剂热法或水热法分别合成了球形单分散的纳米Ni、纳米Ag和纳米Fe₃O₄。纳米银掺杂的钛酸钡陶瓷中无杂相存在，纳米银和钛酸钡不发生反应，当银含量大于5mol％时可观察到金属银相。随着银含量的增加，陶瓷的相对密度先增大后减小然后再增大，陶瓷的介电常数一直增大，而介电损耗则先减小后增大。银掺杂量为1mol％的陶瓷具有较好介电性能。5、采用固相法制备了不同银掺杂量的X7R型钛酸钡陶瓷。在烧结过程中，银与钛酸钡不发生反应，金属银粒子均匀地分布于X7R陶瓷中。少量银（＜0.5mol％）掺杂能够提高X7R钛酸钡陶瓷的烧结密度和介电常数，较多的银（0.5～2mol％）掺杂则会降低陶瓷密度和介电常数，而更多的银（＞2mol％）掺杂又会提高陶瓷的密度和介电常数。银掺杂对容温变化率影响不大，对介电损耗的影响不明显。当银掺杂量为0.5mol％时，陶瓷具有较好的介电性能。更多还原

【Abstract】 BaTiO₃ with a perovskite structure is noteworthy for their exceptional dielectric, piezoelectric, electrostrictive, and electrooptic properties with corresponding electronics applications, and is mostly used to make multilayer ceramic capacitor （MLCC） materials. Sol-gel process has been intensively studied, because it is so effective to give ceramic powders of high purity, small size and good homogeneity. But the BaTiO₃ nanopowders synthesized by sol-gel process however are easy to form agglomeration. Therefore, in this paper, better dispersed BaTiO₃ nanopowders and ceramics with well dielectric properties were prepared by sol-gel process using undersaturated organic acid, organic monoacid and diacid assistant. Moreover, Ni, Ag, and Fe₃O₄ nanoparticles were synthesized by hydrothermal or solvothermal method using oleic acid （OA） as surfactant. And nanosized Ag doped BaTiO₃-based ceramic with high dielectric constant were prepared. Furthermore, on the base of our original X7R materials, Ag-doped X7R BaTiO₃-based ceramic with high dielectric constant were prepared.1. BaTiO₃ powders were prepared by sol-gel process using OA as surfactant, and the powders were all nanometer scale with a particle size ranging from 20 to 50nm. With the increase of the concentration of OA, the dispersibility of the powders was improved. After sintering, the ceramics were completely consisted of the tetrahedron BaTiO₃ phase. The relative density of the ceramic （[Ti（OBu）₄]/[OA] ratio of 1:1） calcined at 900℃for 2h and sintered at 1250℃for 2h was 98.5%, room temperature permittivity reached 4569, and the dielectric loss was 0.027.2. BaTiO₃ powders were prepared by sol-gel process using five kinds of organic acid as surfactant, and the powders were all nanometer scale with a particle size ranging from 20 to 55nm. As the length of carbon chain of the organic acid increases, the size of the powders first increases and then decreases, and the grain size and the relative density of the ceramics increased except the ceramic prepared using stearic acid as the surfactant. Specially, the powders prepared using dodecanoic acid as surfactant had the minimum size, the best dispersibility, and the shape tended to be spherical, and the as-prepared ceramic was fairly uniform and of better grain size （1.05μm）. The permittivity of the ceramic reached 4319 and dielectric loss was 0.022.3. BaTiO₃ powders were prepared by sol-gel process using two kinds of organic diacid （hexanedioic acid and decanedioic acid） as surfactant, and the powders were all nanometer scale with a particle size ranging from 50 to 65nm. The relative density of the ceramic prepared using decanedioic acid as the surfactant was 97.1% and the room temperature permittivity reached 3270. Compared with monoacid, as the carboxyl number increases, the size of the powders obviously increased and the grain size, the relative density and the whole permittivity of the as-prepared ceramics also increased. As the length of carbon chain of the diacid increased, the grain size decreases slightly and the relative density of the ceramics increased. Moreover, compared with OA, the size of the powders prepared using diacid as surfactnat was bigger, and the relative density w as lower. The bigger original particle size was resulted from the bigger "organic acid micro-capsules" which was more stable and could contain more BaTiO₃ precursor. After calcining, the structure is preserved to produce bigger original particle. The bigger the original particle is, the bigger the agglomeration4. Uniform spherical monodispersed Ni, Ag and Fe₃O₄ nanoparticles were synthesized by hydrothermal or solvothermal method. No phases other than BaTiO₃ and Ag were present in nanosized Ag-doped ceramics, which suggersted that no reaction took place between Ag and BaTiO₃. The phase of silver metal can be observed when the content of Ag was higher than 5mol%. The relative density of the ceramics increased first and then decreased, finally increased again. The dielectric constant increased all the time and the dielectric loss first decreased and then increased. When the content of silver is 1mol%, the ceramic had the better dielectric properties. 5. X7R BaTiO₃ ceramics with different content of Ag has been prepared by the traditional solid-state method. No reaction took place between Ag and BaTiO₃ during sintering process, and silver metal dispersed uniformly in the ceramics. A small amount （<0.5mol%） of silver can improve the relative density and dielectric constant of X7R BaTiO₃ ceramics; larger addition （0.5～2mol%） of silver may decrease it; then addition of more silver （>2mol%） can increase theε_r（room temperature dielectric constant） greatly. The silver doping can’t directly affect the TCC （Temperature Coefficient of Capacitance） characteristics, and can’t obviously affect the dielectric loss. When the content of silver is 0.5mol%, the ceramic had the better dielectric properties.更多还原