In Situ Determination of Phase Equilibria and Thermal Expansions in the Ternary Hafnia-Tantala-Titania System

非技术描述：相图的确定，设计新材料的基本热力学是一个漫长而艰巨的过程，但有必要提供新的电子和结构陶瓷所依据的基本科学知识。这项研究的重点是如何加速和改进这类资料的收集，从而采用可应用于与技术有关的系统的新方法。这项研究采用的方法是在高达4000华氏度的空气温度下进行原位测量，使用高强度、快速的x射线同步加速器测量和精确的数据分析。据估计，在目前确定相图所需时间的五分之一内，可以获得更多的科学信息，并且比通常获得的晶体学信息要多得多。一名博士生和几名本科生参与了这项研究。此外，PI还参加各种各样的活动，以促进科学和工程的初高中学生。技术细节：本研究旨在展示一种新的、高效和高度精确的方法来确定三元相图，使用快速、原位、空中同步加速器仪器，再加上Rietveld方法精确、定量的数据分析。这项工作旨在彻底改变收集数据的缓慢、非原位方法，并将这一过程减少五倍。此外，将分析三元相图中发现的任何新相的热膨胀系数和晶体结构。选择铪-钛-钽三元体系作为模型体系。三元制在很大程度上尚未被探索，但即使是这些元素在技术上也很有趣。例如，钽是广泛应用于微电子和集成微技术的有前途的候选下一代材料。它的介电常数是二氧化硅的六倍。钽化合物的应用包括：计算机动态随机存取存储器（dram）中存储电容器的介电层、场效应晶体管中的栅极氧化物、薄膜电致发光器件中的绝缘层、生物和化学传感器中的传感器层、硅太阳能电池的抗反射涂层、电荷耦合器件和耐腐蚀材料。铪是一种很好的中子吸收剂，用于核反应堆的控制棒，而钽酸铪在结构核应用中很有价值。氢氧化铝也被用作超高温结构和隔热材料。这项工作是及时的，因为目前对下一代电子器件的研究是基于掺杂的非晶钽，尽管晶体钽的介电性能明显优于非晶钽，但目前对晶体钽的亚稳相和稳定相的了解是未知的。一个额外的战略利益是培养博士生在这个前沿的研究技术。同时，本科生也参与到研究中来，帮助制作同步加速器实验的样品，并协助进行全天候的束流线实验。PI参与各种活动，向初高中学生推广科学和工程知识（例如，面向小学和高中教师的Project Lead The Way，以及面向女孩的工程体验游戏）。

NON-TECHNICAL DESCRIPTION: The determination of phase diagrams, the underlying thermodynamics for designing new materials is a long and arduous process, but it is necessary to provide the basic scientific knowledge upon which new electronic and structural ceramics are based. This research is focused on how to accelerate and improve the gathering of such information, thereby introducing new methodology which can be applied to technologically-relevant systems. The approach taken in this research is to make in situ measurements at temperatures up to 4,000 F in air, using high intensity, rapid X-ray synchrotron measurements coupled with accurate data analysis. It is estimated that more scientific information can be obtained in one-fifth of the time currently taken to determine a phase diagram, with significantly more crystallographic information than what is usually obtained. A doctoral student and several undergraduate students are engaged in the research. As well, the PI participates in a variety of activities to promote science and engineering to middle and high school students.TECHNICAL DETAILS: This research aims to demonstrate a new, efficient and highly accurate method to determine ternary phase diagrams, using rapid, in situ, in air synchrotron instrumentation, coupled with accurate, quantitative data analysis by the Rietveld method. This work aims to revolutionize the slow, ex situ methods of collecting data and reduce the process five-fold. In addition, thermal expansion coefficients and crystal structures will be analyzed for any new phases discovered in the ternary phase diagram. The hafnia-titania-tantala ternary was selected as the model system. The ternary system is largely unexplored, but even the elements are technologically interesting. For example, tantala is a promising candidate next generation material for application in a wide range of microelectronics and integrated micro-technologies. Its dielectric constant is six times that of silica. Tantala compounds have applications as dielectric layers for storage capacitors in dynamic random access memories (DRAMS) in computers, gate oxides in field effect transistors, insulating layers in thin film electroluminescent devices, sensor layers in biological and chemical sensors, anti-reflection coatings for silicon solar cells, charge-coupled devices and corrosion resistant materials. Hafnium is a good absorber of neutrons and is used in the control rods of nuclear reactors and hafnium tantalate is of interest for structural nuclear applications. Hafnia is also used as an ultra-high temperature structural and thermally insulating material. This work is timely because current research into the next generation of electronic devices is based on doped, amorphous tantala, and the current knowledge of metastable and stable phases in crystalline tantala is unknown, even though its crystalline dielectric properties are significantly superior to its amorphous properties. An additional strategic benefit is the training of a doctoral student in this cutting-edge research technique. As well, undergraduate students are engaged in the research by helping to make samples for the synchrotron experiments and assisting at the around-the-clock beam line experiments. The PI participates in a variety of activities to promote science and engineering to middle and high school students (e.g., Project Lead the Way for grade school and high school teachers, and GAMES (engineering experiences for girls).