CEAE Distinguished Speaker Series: Making Better Materials - From Understanding 2D Interfacial Phases to Exploring Compositionally Complex Ceramics and Ultrafast Sintering

A piece of ice melts at 0 °C, but a nanometer-thick surface layer of the ice can melt at tens of degrees below zero. This phenomenon, known as “premelting,” was first recognized by physicist Michael Faraday. Materials scientists have discovered that interfaces in engineered materials can exhibit more complex phase-like transitions at high temperatures [see, e.g., a most recent perspective: Science 368, 381 (2024)], which can affect the processing and properties of a broad range of metallic alloys and ceramic materials. Studies of 2D interfacial phases (also called “complexions”) shed light on several long-standing mysteries in materials science, including the origins and atomic-level mechanisms of “solid-state” activated sintering, as well as liquid metal embrittlement in Ni-Bi and grain boundary (GB) embrittlement in Ni-S. Since phase diagrams are arguably one of the most useful materials science tools, a focus of this seminar is to discuss a series of studies to compute GB “phase” diagrams via thermodynamic models, atomistic simulations, and machine learning [see a perspective: Interdisciplinary Materials 2, 137 (2023)]. Analogous 2D surface phases have also been studied and utilized to improve the performance of batteries and other materials for energy-related applications. After briefly discussing two other ongoing studies on (i) ultrafast sintering (in seconds) with vs. without electric fields and field effects on microstructural evolution and (ii) 5- to 21-component high-entropy and compositionally complex ceramics, nascent topics at the intersections of these emergent areas and interfacial science will be discussed. Here, recent collaborative studies within the UCI MRSEC CCAM investigated disordered (premelting-like) GBs in compositionally complex perovskite oxides and their roles in lithium ionic conduction and abnormal grain growth. In addition, we demonstrated that applied electric fields can induce GB phase-like transitions via electrochemical coupling, thereby opening a new window to tailor microstructures [Materials Today 73, 66 (2024)].