Bulk silicon nitride (Si3N4) ceramics have been investigated extensively over the last twenty years due to their desirable mechanical and physical properties in many high temperature applications. An intrinsic characteristic of Si3N4 ceramics, on the other hand, is their brittleness (fragility), which limits their use and reliability as structural components. It has been demonstrated that doping the grain boundaries of Si3N4 with rare-earth oxides decreases this intrinsic brittleness, and improves its mechanical properties. In this program, the aim is to take a significant step in a fundamental atomic understanding of the structure-property relationships of Si3N4 grain boundaries by using advanced methods of structural and electronic characterization in state-of-the-art scanning transmission electron microscopes and state-of-the-art first-principles (parameter-free) calculations. Such atomic understanding is the most important step in achieving a real breakthrough in tailoring the mechanical properties of Si3N4 for better device applications. Additionally, this work includes significant training of undergraduate and graduate students in the most advanced experimental characterization methods and computational modeling studies, used in the research and development industry. Training students along both experimental and theoretical disciplines is a unique aspect of the proposed activity, and is expected to offer a wider range of career opportunities for the students in the current competitive job market.
In this program, the PIs propose to investigate the structure-property relationships in the Si3N4/rare-earth oxides interfaces using two state-of-the-art experimental and computational modeling techniques: (1) atomic-resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM), and (2) first principles calculations based on density functional theory (DFT). The experimental methods that will be used in these studies have already been shown to provide unique information on the link between structure, bonding, and composition of these interfaces with the material properties of silicon nitride. DFT, with this very good track record in computational materials science, is the most widely used theoretical tool to accurately study structure-property relationships in structurally and chemically complex materials. In particular, in the proposed research program the PIs, using a unique combination of these experimental and theoretical techniques, aim to understand how the interfacial atomic and electronic structures are controlled by oxygen and the size/electronic structure of the different rare-earth elements. This information is crucial in order to achieve a real breakthrough in tailoring the mechanical properties of Si3N4 for better device applications. Additionally, this work includes significant training of undergraduate and graduate students in the most advanced experimental characterization methods and computational modeling studies, used in the research and development industry. Training students along both experimental and theoretical disciplines is an important aspect of the proposed activity, and is expected to offer a wider range of career opportunities for the students in a competitive job market.
