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

非技术描述：相图的确定是设计新材料的热力学基础，这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基于的基本科学知识。这项研究的重点是如何加快和改进此类信息的收集，从而引入可应用于技术相关系统的新方法。这项研究采取的方法是在空气中温度高达4,000华氏度的情况下进行现场测量，使用高强度、快速的X射线同步加速器测量并结合准确的数据分析。据估计，在目前确定相图所需时间的五分之一时间内就可以获得更多的科学信息，比通常获得的结晶学信息要多得多。一名博士生和几名本科生参与了这项研究。技术细节：这项研究旨在展示一种新的、高效和高精度的方法来确定三元相图，该方法使用快速、现场、空气中的同步加速器仪器，并结合Rietveld方法进行准确的定量数据分析。这项工作旨在彻底改变缓慢的、异地收集数据的方法，并将这一过程减少五分之一。此外，还将分析在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Hafnia-TiO2-Tantala三元体系作为模型体系。三元系统在很大程度上还没有被探索，但即使是元素在技术上也是有趣的。例如，Tantala是一种很有前途的下一代材料，可以应用于广泛的微电子和集成微技术。它的介电常数是二氧化硅的六倍。Tantala化合物可用作计算机动态随机存取存储器(DRAM)中存储电容器的介质层、场效应晶体管中的栅氧化物、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、硅太阳能电池的减反射涂层、电荷耦合器件和耐腐蚀材料。Hf是一种很好的中子吸收剂，用于核反应堆的控制棒，而Hf-Ta酸盐在结构核应用中具有重要意义。哈夫尼亚还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设备的研究是基于掺杂的非晶态钽酸锂，而且目前关于晶体钽酸锂亚稳定相和稳定相的知识是未知的，尽管它的晶态介电性能明显优于它的非晶态属性。另一个战略好处是对博士生进行这种尖端研究技术的培训。此外，本科生也参与了这项研究，他们帮助制作同步加速器实验的样品，并协助全天候束线实验。该协会参与了向初中生推广科学和工程学的各种活动(例如小学和高中教师带头的项目)和游戏(女孩的工程学经验)。

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).