【作者】 李玉芬；

【导师】 刘晓林；

【作者基本信息】 北京化工大学 ， 化学工程， 2007， 硕士

【摘要】 本文以典型钙钛矿结构的BaTiO₃为研究对象，分别采用氢氧化物-醇盐法（简称AH法）和溶剂热重结晶法（SV法）系统地研究了纳米BaTiO₃的制备工艺并对所得粉体进行了表征。以Ti（i-OC₃H₇）₄和Ba（OH）₂·8H₂O为钛源和钡源，采用AH法，低温下（＜100℃）合成了纳米BaTiO₃粉体。研究表明：粉体粒径随反应时间的增加先减小后增大；随反应温度或钛醇盐浓度的升高而增加；增加反应物Ba／Ti摩尔比使粉体粒径减小。当钛醇盐浓度为1.104M，回流温度下将钡源加入到稍过量的钛源中反应8h，可以得到颗粒分布窄、类球形且粒径约为～13nm的立方相BaTiO₃粉体，HRTEM表明粉体中存在单晶颗粒；粉体经800℃热处理后，可以得到粒径约～60nm，c／a=1.0097的四方相BaTiO3。以Ba（OH）₂取代部分Ba（OH）₂·8H₂O（Ba（OH）₂／Ba（OH）₂·8H₂O=R）发现粉体粒径随R的增加而减小，不同反应时间粉体的XRD和TEM结果表明BaTiO₃颗粒的形成过程遵循溶胶-沉淀机制，提高反应温度及减小R均可加快生成BaTiO₃的速率。其次，对AH-BaTiO₃浆料进行溶剂热重结晶处理，研究发现处理后粉体的结晶度提高，形貌更加规整且羟基缺陷减少。粉体的粒径随着溶剂热处理温度的升高及溶剂热处理时间的延长而增大。提高前驱物Ba／Ti摩尔比会减少晶胞中的羟基缺陷，有利于四方相钛酸钡的生成。当氨水／乙醇为2／3，Ba／Ti摩尔比为2，前驱物固含量为0.4g／ml，190℃下处理3h可得到形貌规整且平均粒径约为25nm的四方相BaTiO₃。最后，研究了BaTiO₃粉体的烧结活性和介电性能，AH-BaTiO₃粉体在1000℃烧结就可以得到相对密度为94.5％BaTiO₃陶瓷，比SV-BaTiO₃粉体达到相同致密度所需的烧结温度约低200℃，表明小尺寸粉体具有高的烧结活性。由于SV-BaTiO₃粉体具有较少的缺陷及较高的原始密度，与AH-BaTiO₃粉体相比，烧结成瓷后室温介电常数有所提高，从2055增加到2608，介电损耗从0.035降至0.02。更多还原

【Abstract】 Nano-sized BaTiO₃ powders were prepared by an alkoxide-hydroxide process and a solvothermal recrystallization route, respectively.Firstly, in the alkoxide-hydroxide process Ba（OH）₂·8H₂O, Ti（i-OC₃H₇）₄ and hydrous ethanol were acted as barium source, titanium source and reactive medium, respectively. The results showed that higher reaction temperature or titanium alcoholic concentration tended to increase the particle size of powders and siutbale reaction time and Ba/Ti were benifit to obtain finer powders. Under refluxing conditions, when added Ba（OH）₂·8H₂O to Ti alcoholic solution and reacted for 8h, nanosized BaTiO₃ particles with mean size of-13 nm, few aggregates and cubic structure was obtained. HRTEM revealed single-crystal particles existed in powders. Calcining the as-prepared powders at 800, tetragonal BaTiO₃ （c/a=1.0097） with particle size of 60nm could be obtained.Furthmore, BaTiO₃ powders were synthesized by a modified AH route, that was replacing part of the Ba（OH）₂·8H₂O by hydrous Ba（OH）₂ to change the water content of the reaction system. It was found that the powders particle size increased with reduce of R in barium sources and AH route was a sol-precipitation process. Hydrolysis of titanium alkoxide depended on the release of water molecules in situ Ba（OH）₂·8H₂O dissolved in the alcoholic solution. Thus, smaller R in barium source or lower reaction temperature would slow down the hydrolysis rate of Ti alkoxide.In order to process the crystallinity of the BaTiO₃ obtained by AH process, a novel solvothermal recrystallization （SV） route was developed to obtain finer BaTiO₃ nanocrystals. The results showed that the SV-BaTiO₃ powders had much less hydroxyl lattice defects, higher purity and better crystallinity than AH-BaTiO₃. Higher solvothermal treatment temperature and time were favorable for the preparation of nice crystallinity and larger particle size of BaTiO₃ powder. Higer Ba/Ti of the precursor was benefit to produce tetragonal BaTiO₃. When fixed the ammonia/enthnal of 2/3, Ba/Ti molar ratio in precursor of 2, solvothermal temperature of 190℃, recrystalling time of 3h and the concentration of BaTiO₃ slurry of 0.4g/ml, tetragonal BaTiO₃ powders with mean size of 25nm could be obtained.Finally, the sintering reactivity and delectric properties of BaTiO₃ ceramic were investigated. It was found that AH-BaTiO₃ ceramics had a relative low sintering temperature and could be sintered at 1000℃with relative density of 94.5%, which was lower than that obtained by solvothermal recrystallization route. Compared with the untreated powders, due to the less hydroxyl lattice defects content and higher density of crude pellet, the dielectric constant of BaTiO₃ ceramics increased from 2055 to 2608 at room temperature, while the delectric loss reduced from 0.035 to 0,02,更多还原