Structure-Property-Chemistry Relationship in Ferroelectric Bronzes: Material Science Issues in Tilted Oxygen Octahedra

本研究项目的主要目标是发展钨青铜（TB）结构固溶体的基础材料科学，丰富目前对氧八面体铁电材料和弛豫剂的一般认识，从而提高设计、选择和修饰电子陶瓷和单晶的能力，用于各种器件应用。具体的研究课题包括：(a)结核成分结构场图的构建；(b)单晶x射线衍射晶体结构研究；(c)了解弛豫特性和结构性质的阳离子/空位分布和顺序；(d)大阳离子的热力学涨落对低温介质色散的影响。该项目将包括关键的实验和分析，以澄清铁电TB氧化物家族中潜在的结构-性能-化学关系。将构建已知TB成分的结构场图，总结离子半径和压力/温度条件下的晶体相稳定性。因此，可以绘制和预测嗜形相边界（MPB）系统。单晶衍射可以在很宽的温度范围内得到阳离子位移的细节。设计并建立了一个选择电场条件下的单晶x射线衍射和结构精化系统。这将是第一个允许在电场下研究阳离子位移的仪器。对a位填充或部分填充的近MPB成分单晶进行淬火和退火研究，以阐明阳离子偏好和空位分布的影响。低温相变/弛豫现象将通过结构分析（低温XRD和中子衍射）以及动态热释电测量来研究。该项目将为PSU和林肯大学（HBCU）的学生提供一个智力和具有挑战性的研究项目，并可以使用大学和政府的实验室设施。钨青铜结构的铁电材料涵盖了一大类固溶体体系，在各种电子、光学和电光领域具有巨大的应用潜力。该项目将使材料科学家对变形和倾斜氧八面体结构中的结构-性能-化学关系有更统一的理解，并为技术上重要的设备应用提供智能选择材料的可能性。＊＊＊

The primary goal of this research project is to develop underlying materials science in solid solutions of tungsten bronze (TB) structure and to enrich the present general understanding of the oxygen octahedral ferroelectric materials and relaxors, thereby enhancing the capability to design, select and modify electronic ceramics and single crystals for various device applications. Particular research topics include (a) the construction of structure-field-maps for TB compositions; (b) crystallographic structure studies by single crystal x-ray diffraction; (c) understanding the cation/vacancy distribution and order on relaxor characteristics and structural properties; and (d) the effect of thermodynamic fluctuation of large cations on low temperature dielectric dispersions. The project will consist of critical experiments and analysis that clarify the underlying structure-property-chemistry relationship in the ferroelectric TB oxide family. A structure-field-map for known TB compositions that summarizes crystallographic phase stability over ionic radii and pressure/temperature conditions will be constructed. Morphotropic phase boundary (MPB) systems can therefore be charted and predicted. Single crystal diffraction will be conducted to obtain cationic displacement details in over a broad temperature range. A selected-electric-field-condition single crystal x-ray diffraction and structure refinement system will be designed and built. It will be the first of its kind to allow the study of cation displacement under an electric field. Quenching and annealing studies on single crystals of near MPB composition with filled or partially filled A-site will be carried out to clarify the effect of cation site-preference and the vacancy distribution. Low temperature phase transition/relaxation phenomena will be studied by structural analysis (low temperature XRD and neutron diffraction), along with a dynamic pyroelectric measurement. The project will provide students from PSU and from Lincoln University (an HBCU) with an intellectual and challenging research project with access to both university and government lab facilities. Ferroelectric materials of the tungsten bronze structure encompass a large family of solid solution systems with great potential in various electronic, optical and electro-optic applications. The understanding that will result from this project will take materials scientists toward a more unified understanding on the structure-property-chemistry relations in deformed and tilted oxygen octahedral structures, and allow the possibility of intelligent selection of the materials for technologically important device applications. ***