CAREER: Toward Rational Discovery and Design of Metastable Materials

Colorado School Of Mines, Golden CO

Investigators

Abstract

NONTECHNICAL SUMMARY Metastable forms of matter are long-lived in environments and conditions at which they would tend to transform to more thermodynamically favorable stable forms. There are many examples of such materials in our daily lives. The best-known example is diamond, a crystalline form of carbon that is known to be metastable at room temperature and ambient pressure. At these conditions diamond would tend to spontaneously transform into graphite, but this process is extremely slow making diamond sufficiently long-lived (metastable) so that its mechanical, optical and electronic properties can be utilized in a number of technologically relevant applications. Other well-known examples are glass, which is a non-crystalline metastable form of silicon dioxide, and solid chocolate in the so-called polymorph-V form, which is its most utilized form due to its desired melting, textural and mouth-feel characteristics. Despite the proven importance of metastable materials and despite a rather extensive knowledge of the phenomenology of metastability, our ability to predict and design metastable forms of matter for a specific purpose is rather limited. Significant knowledge gaps remain that prevent accurate predictions of which metastable states, out of the numerous possibilities, could actually be experimentally realized and how long they would tend to remain in that state. The main scientific goal of this project is to fill these knowledge gaps in order to enable rational and reliable discovery and design of metastable materials. More specifically, this project concentrates on theory developments to advance our understanding and our ability to predictively model the realizability of metastable states and the kinetics of their transformations to thermodynamically more stable forms. This will be achieved through a combination of modern electronic structure methods and molecular dynamics simulations, as well as by leveraging previous accomplishments of the PI and the existing capabilities present in his group. The educational and outreach activities of this project aimed to integrate the newly generated knowledge include: (i) development of innovative course materials designed to promote student engagement and active learning, (ii) increasing participation of undergraduates in research both through opportunities created by this project, and continuing participation in the Department of Energy Science Undergraduate Laboratory Internships program at the National Renewable Energy Laboratory, and (iii) strengthening PI’s role in the Bridge Opportunities for Transfer Student Success program at the Colorado School of Mines that seeks to both recruit and retain transfer students from community colleges through summer research experiences. Educational and outreach activities will also include organization of tutorials and symposia at major materials science and condensed matter physics conferences as well as dissemination through publications and presentations. TECHNICAL SUMMARY Metastable systems, both crystalline (polymorphs) and non-crystalline (glassy, amorphous), offer a vast and immensely rich, but virtually unexplored space for discovering novel and useful materials. While there are many examples of metastable materials in our daily lives (e.g. diamond, glass, chocolate, anatase), our present understanding of metastability is largely phenomenological and qualitative. First, we are only beginning to understand the realizability of metastable polymorphs; that is, why there is only a small number of structures realized experimentally in comparison to the large number of possible low-energy states. Second, unlike the ground states which are stable, the metastable states have finite lifetimes and our ability to predict kinetics of transformations between different phases is presently rather limited. These remarks also apply to our understanding of the structure-property relations; we understand much better how changing the chemistry would affect relevant properties of materials compared to what would happen if the structure changed. The main goal of this project is to fill these knowledge gaps; with the specific objectives which include: (i) extending our understanding of physical principles governing realizability of metastable crystalline phases, (ii) enabling predictive modeling of glassy and amorphous states, and (iii) revealing physical principles governing kinetics of transformations between different crystal structures. This will be achieved through a combination of modern electronic structure methods and molecular dynamics simulations, as well as by leveraging previous accomplishments of the PI and the existing capabilities present in his group. The work is founded on the hypotheses that the realizability of metastable solids, in particular crystalline polymorphs, is determined by their thermodynamic probabilities and that the dominant contributions to the rapid or slow nature of the kinetics of polymorphic transformations are primarily crystallographic. These hypotheses, which are partially validated in the PI’s preliminary work, form a basis to both advance our present state of knowledge of metastability and for creating powerful and efficient computational methodologies that would enable identification of new and potentially ground-breaking metastable functional materials. The educational and outreach activities of this project aimed to integrate the newly generated knowledge include: (i) development of innovative course materials designed to promote student engagement and active learning, (ii) increasing participation of undergraduates in research both through opportunities created by this project, and continuing participation in the Department of Energy Science Undergraduate Laboratory Internships program at the National Renewable Energy Laboratory, and (iii) strengthening PI’s role in the Bridge Opportunities for Transfer Student Success program at the Colorado School of Mines that seeks to both recruit and retain transfer students from community colleges through summer research experiences. Educational and outreach activities will also include organization of tutorials and symposia at major materials science and condensed matter physics conferences as well as dissemination through publications and presentations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.