【作者】 肖立华；

【导师】 孟庆昌；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 硕士

【摘要】 本文采用溶胶-凝胶法(Sol-gel)通过紫外光辐照合成了钕掺杂钛酸铋BNT (Bi4-xNdxTi3O12, x=0, 0.25, 0.5, 0.75)粉体和薄膜。通过热重-差热分析(TG-DTA)、X射线衍射(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)等技术手段对Sol-gel法制备的BNT粉体和薄膜进行了表征。BNT溶胶胶体制备工艺优化过程表明,采用醋酸铋和硝酸钕及钛酸四丁酯为原始组分,乙酸和乙二醇分别为催化剂和溶剂,可获得BNT透明溶胶。在凝胶过程中,经紫外光辐照下制备的BNT(x=0.25)干凝胶粉体,在350-400℃煅烧时主物相是Bi2O3和Bi2O3CO2,而在450℃煅烧处理可获得单一钙钛矿相BNT。紫外光辐照显著地的降低了BNT的晶化温度。研究表明,紫外光辐照促进了凝胶在晶化过程中的化学反应:通过溶胶-凝胶法在Pt(111)/Ti/SiO2/Si结构的基片上旋涂沉积BNT薄膜,经紫外光辐照的薄膜于300℃除去有机物,后经500℃随炉热处理可得到均匀致密的钙钛矿相BNT薄膜。薄膜平整致密,厚度约为400nm。薄膜择优取向随着Nd掺杂含量的增加趋向于c轴,其中以x=0.5,c轴择优取向最为明显。所得薄膜具有较小的粗糙度,均在2-4nm范围内。铁电性能测试结果表明,剩余极化强度(Pr)和矫顽场(Ec)都随着Nd掺杂比例的增大而减小。Bi4-xNdxTi3O12(x=0.25, 0.5, 0.75)薄膜的剩余极化值分别为2.75μC/cm2,11.59μC/cm2,10.24μC/cm2,其中钕掺杂量x=0.5的薄膜表现出良好的铁电性能。更多还原

【Abstract】 With the help of ultraviolet irradiation, the ferroelectric BNT(Bi4-xNdxTi3O12, x=0, 0.25, 0.5, 0.75) powders and thin films were successfully synthesized by a sol-gel method. The crystallization process and structural characteristics of obtained BNT powders and thin films were analyzed by using TG-TDA, XRD, SEM and AFM methods.The transparent BNT solutions were prepared by using Bi(CH3COO)3 and Nd(NO3)3·5H2O, and Ti(C4H9O)4 as source materials, ethylene alcohol as a solvent and acetic acid (HOAc) as a catalyst. Under the condition of ultraviolet irradiation, the main constitutions of the BNT gel calcined at the range of 350°C to 400°C are Bi2O3 and Bi2O3CO2. The phase-pure BNT with layered pervoskite structure can be obtained at as lower as 450°C. It indicates that the ultraviolet irradiation play a very important role in the crystallization process of the dried gel. It is considered that the ultraviolet irradiation promotes the chemical reactions as follows.In the case of preparation of BNT thin films, also under the condition of ultraviolet irradiation, the organic matter was burned at 300°C. After the heat-treatment at 500°C, the phase-pure ferroelectric thin films can be synthesized with a dense surface. The typical thickness of the thin films was 400nm. With the increasing of Nd content, the optimal orientation of BNT thin films was adapted to c axis. In particular, the Bi3.5Nd0.5Ti3O12 thin film is more (00l)-orientated than other thin films. Accordingly, the thin films were homogenously, and have small roughness at a level of 2-4 nm. With the change of chemical constitution of Nd and technical conditions, the optimal BNT thin film (x=0.5) has the residual polarization of 11.59μC/cm2, which is good enough for applications in the future.更多还原