Bi4Ti3O12基共生铋层状铁电单晶的生长及其结构与性能关系研究

Bi4Ti3O12-SrBi4Ti4O15 (BiT-SBT) is a representative kind of intergrowth bismuth layer-structured ferroelectric materials, which has been attracted much attention due to its superlattice-structure as well as high Curie temperature and other excellent electrical properties. The BiT-SBT and Nd/La-modified BiT-SBT crystals are expected to exhibit superior piezoelectric properties than those of ceramics. In this project, the top-seeded solution growth (TSSG) technique is employed to grow BiT-SBT single crystal, and the seed crystal is obtained by sieve method. The high quality BiT-SBT and Nd/La-modified BiT-SBT single crystal with diameter over 10mm can be obtained by optimizing growth parameters, such as growth speed, the rotation rate of seed and the proportion of Bi2O3 flux etc. In addition, the segregation will be studied to improve the homogeneity of the crystal. Dielectric, piezoelectric and ferroelectric properties are to be systemically investigated as functions of temperature, frequency, composition and crystal orientation. Moreover, the relationship among electronic structure, ionic displacement and electric properties are to be studied by experimental methods and first-principles, revealing the possibility of high piezoelectric in BiT-SBT single crystal high index orientation, which greatly provide the technical foundation and theoretical basis to promote the application of bismuth layer-structured piezoelectric single crystals.

Bi4Ti3O12－SrBi4Ti4O15（简称BiT-SBT）是一类典型的共生铋层状铁电体材料，因具有天然超晶格结构及高居里温度、高铁电压电性能而被引起广泛关注，预计共生铋层状BiT-SBT单晶及Nd/La改性单晶将表现出比陶瓷更为优越的铁电压电性能。本项目拟采用顶部籽晶助熔剂法生长BiT-SBT系及其Nd/La改性单晶，利用逐步淘汰法培育BiT-SBT籽晶，通过调整生长速度、籽晶旋转速率、Bi2O3助熔剂添加比例等晶体生长工艺参数，弄清单晶生长中组分分凝规律，以期最终生长出直径大于10mm、质量优异的BiT-SBT系及其Nd/La改性单晶，并将对所得到单晶的压电、铁电、介电等性能进行系统表征；在实验研究基础上，利用第一性原理研究该单晶电学性能与其电子结构、离子位移等微观物理量的关系，并探索BiT-SBT系单晶高指数方向高压电性能的可能性，为推动铋层状单晶的应用提供技术基础和理论依据。

本项目采用熔融法生长制备出Bi4Ti3O12(BIT)单晶，对BIT单晶材料的制备工艺、生长机理以及晶体结构进行了系统探究。所制备出的淡黄色单晶样品尺寸约为10mm×10mm×5mm，使用XRD、SEM、TEM等测试手段对晶体结构进行全方位表征分析。XRD图谱分析表明生成了BIT主晶相，样品截断面SEM照片显示单晶具有二维生长特性，自然显露面为(001)，TEM得到的晶格条纹图中可以看出(117)面天然超晶格条纹，面间距为0.296nm，研究表明采用熔融法并控制合适的降温速率可以制备出单晶样品，这一结果为制备更高质量的BIT单晶材料的制备与性能研究打下重要的基础。本项目还对BIT基共生铋层状陶瓷材料的制备工艺、晶体结构和各项物理性能进行了系统研究，采用固相法制备了Na0.5Bi8.5Ti7O27(NBT-BIT)共生铋层状无铅压电陶瓷材料，研究了不同离子掺杂组分对陶瓷材料的性能和缺陷机制的影响，获得了Er3+、Ce3+、Mn3+等离子对BIT基共生铋层状陶瓷材料压电、铁电、介电性能随温度、应力和电场变化的作用规律，探讨了缺陷对陶瓷各方面性能的优化作用，结合稀土离子光致发光特性综合探讨了掺杂对体系结构和性能的影响机制。研究成果对BIT基共生铋层状材料在高温应用领域中实现光电多功能一体化进程具有重要推动作用。