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).
