【作者】 李明利；

【导师】 徐明霞； 梁辉；

【作者基本信息】 天津大学 ， 材料学， 2009， 博士

【摘要】 钛酸锶钡（Ba1-xSrxTiO₃,BST）铁电陶瓷具有优异的电学性能,但是其过高的烧结温度（>1300℃）限制了该材料的实际应用。针对该问题,本课题采用改进的草酸盐共沉淀工艺制备了具有高化学活性的BST粉体,并开发了Bi₂O₃-ZnO-Nb₂O₅ （BZN）、B₂O₃-Li₂CO₃ （BL）、B₂O₃-SiO₂–Li₂CO₃ （BSL）三个体系的烧结助剂,研究了三个材料体系的烧结行为和介电特性。探明了作为草酸盐共沉淀方法制备钛酸锶钡粉体前躯体之一的草酸氧钛酸（HTO）溶液的稳定和失稳机理,提出了制备稳定澄清的草酸氧钛酸（HTO）溶液的条件是既要控制pH的波动又要添加定比例的去离子水以抑制[TiO（C₂O₄）₂]₂-的聚合作用。在此基础上通过向锶钡盐溶液中预先添加固定量的氨水以调控pH值,实现了对整个共沉淀反应过程中pH的精确控制,大幅简化了制备工艺,避免了由于反应体系各处的不均匀性带来的扰动,制备出性能优良的BST粉体。该粉体具有微米级的粒径、高的比表面积和规则的类球状软团聚形貌,因而具有良好的流动性和较高的烧结活性,与传统方法制备的BST粉体相比具有较低的烧结温度和较宽的烧结温区。BST-BZN的烧结温度降低到1050℃以下,在烧结后期BZN与BST发生了固溶反应,BST-BZN的居里峰被压低展宽,因而有良好的介电常数-温度稳定性,其αTin为2.93%,αTde为3.78%。但是由于少量Bi³⁺对Ba²⁺/Sr²⁺的取代、晶粒的细化、晶界相比例增多等原因导致了BST-BZN可调率降低,1kV/mm的偏场作用下其可调率只有0.15%。B₂O₃-Li2O烧结助剂能够显著降低BST的烧结温度,与所制备的BST粉体匹配性良好,当添加2.32wt%Li₂CO₃-0.68wt%B₂O₃时,BST的烧结温度降低到850℃。部分B³⁺和Li+进入BST的晶格导致BST的XRD衍射峰向高角度略微偏移。由于B₂O₃-Li2O的添加量少,BST-BL具有较高的偏场可调性,在1kV/mm的外加偏场下,样品的可调率在15%以上。相对于BST-BL体系,添加SiO₂后,BST-BSL的烧结温度升高。B₂O₃-SiO₂–Li₂CO₃在烧结过程中与BST主晶相发生了复杂的化学反应,因此造成了液相性质的改变,在不同温度保温,残留于晶界的第二相种类不同。由于该BST粉体的显著优点, BST-BSL可以在较宽的温区内实现致密烧结,从而实现对BST晶粒尺寸的控制。B₂O₃-SiO₂–Li₂CO₃的添加大幅改善了BST的介电常数温度稳定性,但是非铁电第二相对BST铁电性的‘稀释作用’使BST-BSL的可调率降低,BST-BSL样品在1kV/mm外加偏场下的可调率在5%以上。更多还原

【Abstract】 Barium Strontium Titanate （Ba1-xSrxTiO₃,BST） ferroelectric materials have excellent electrical properties. Pure BST and BST-based materials are commonly sintered at >1350°C, which is too high for using silver electrodes and co-firing with LTCC multilayer modules （850-900°C）. In this paper, Ba0.6Sr0.4TiO₃ powders with high activity by modified oxalate co-precipitation method were chosen as a basic ferroelectric BST ceramic. The different combination of Bi2O3-ZnO-Nb2O5, B₂O₃-Li₂CO₃ and B₂O₃-SiO₂–Li₂CO₃ were tested as sintering aids. The stabilization mechanism of [H2TiO（C2O4）2] （HTO） was studied. In order to obtain clear HTO solution, the disturbance of pH value must be avoided and proper quantities of H2O must be added to inhibit the polymerization of [TiO（C2O4）2]2-. Through adding quantitative ammonia into a precursor solution containing stoichiometric quantities of Ba and Sr ions before the co-precipitation procedure, a simple oxalate co-precipitation method based one-step cation-exchange reaction between the stoichiometric solutions of oxalotitanic acid （H2TiO（C2O4）2:HTO） and barium+strontium nitrate is investigated successfully for the quantitative precipitation of barium–strontium titanyl oxalate （Ba0.6Sr0.4TiO（C2O4）2·4H2O:BSTO） precursor powders. The pyrolysis of BSTO produced the homogeneous barium–strontium titanate （Ba0.6Sr0.4TiO₃: BST） powders. The BST powders were micron-sized with regular near-spherical aggregate structure. The BST powders possess high fluidity as well as high specific surface area of 18.52g/m2 and thus can be sintered at rather lower sintering temperature and broader temperature range. The BST-BZN samples can be sintered at 1050℃. Also the Curie peak was suppressed and broadened withαTin of 2.93% andαTde of 3.78% in the range of -40-80℃. However, the tunability was only 0.15% when a DC field of 1kV/mm was installed （measured at 1MHz）. It can be explained considering the substitution of Bi³⁺ to Ba²⁺/Sr²⁺, the decrease of BST grain size and the increase of grain boundary. B₂O₃-Li₂CO₃ effectively decreased the sintering temperature of BST. The BST with 2.32wt%Li₂CO₃-0.68wt%B₂O₃ can be sintered at as low as 850°C. Some B³⁺ and Li+ enter the BST crystal lattice. The tunability of BST-BL samples was over 15% when a DC field of 1kV/mm was installed （measured at 1MHz）. BST-BSL can be sintered at relatively higher temperature and broader temperature range. And thus the grain size of BST can be adjusted easily by altering the sintering temperature. The change of liquid property during the sintering process was due to the complex chemical reaction between B₂O₃-SiO₂–Li₂CO₃ and BST. The permittivity-temperature character of BST-BSL was improved while the tunability was decreased. The tunability of BST-BSL samples was over 5% when a DC field of 1kV/mm was installed （measured at 1MHz）.更多还原