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Expanding the frontier—Grand challenges in ceramic science cracks are not appropriate for short, naturally occurring cracks. A new avenue of research is required to help elucidate fundamental mechanisms of nucleation events and to provide grist for lifetime models that more accurately portray reality. 2. Understanding the phase behavior of interfaces The second grand challenge is to expand and redefine the current boundaries of ceramic behavior by exploiting the boundaries within the structure. Often, grain-boundary behavior influences the electrical, thermal, and mechanical properties of bulk, polycrystalline materials. For example, incorporating oversized dopant ions at alumina grain boundaries can influence the high-temperature mechanical and transport behavior. The dopant ions segregate to the grain boundaries. However, the mechanism by which the properties modify is unresolved. A fascinating new development in terms of our view of boundaries is related to the discovery of thermodynamically stable interphases at grain boundaries, referred to as complexions, which do not exist as stand-alone materials. For example, it has been shown that in certain impure alumina ceramics, grain boundaries with distinct structures and compositions have different mobilities, energies, orientation distributions, compositions, and atomic structures. Given the importance of boundaries in determining the overall material properties, this raises the exciting prospect of synthesizing new materials with unique combinations of properties. In principle, therefore, one could begin to colonize the “white space” in Ashby diagrams, which are the locations of contraindicative properties, such as simultaneous high hardness and toughness, on property correlation maps. 3. Predicting and controlling heterogeneous microstructures with unprecedented functionalities Multiphasic combinations of ceramics and hybrid combinations with other materials offer the potential to realize functionalities well beyond the limits of present-day materials. However, achieving unprecedented functionalities will require a fundamental understanding and control of constituent properties, interfaces, and microstructures at length scales across several orders of magnitude. The challenge for the future is to merge this information at various length scales and to conduct such studies as a function of the fourth dimension, time, to develop a fundamental understanding of the evolution of the microstructure and its effect on properties. Several advancements are needed. First, to gain a comprehensive understanding of a mechanism, structural characterization will need to integrate multiple techniques to span several orders of magnitude of length scales. A second barrier is the need to analyze at high scanning rates large volumes of material that contain more of the features of interest (such as second-phase particles and interfaces). Even defining the representative volume of material required to understand the origin of a given property remains a challenge. A third challenge is to develop more facile approaches to collect timedependent information from multiple trials using destructive and nondestructive imaging techniques. 4. Controlling the properties of oxide electronics The past 15 years of research on oxide single crystals and thin films provide great insight to the diverse spectrum of electronic, optical, and magnetic properties of ceramic oxide materials that were historically categorized as passive insulators. For example, precise control of the LaAlO3/ SrTiO3 interface demonstrates that joining two linear dielectrics can lead to a high-mobility electron gas. The future challenge is to design and synthesize oxide surfaces, interfaces, and nanoscale structures that catalyze a wide spectrum of scientifically inspiring electronic properties, including high mobility, superconductivity, and magnetism, that are tunable by external electrical, optical, magnetic, mechanical, and chemical stimuli. Next-generation oxide electronics will require significant synergy between materials theory, modeling, synthesis, characterization, and nanomanufacturing. Major scientific advances are required, including a sophisticated ability to control stoichiometry, strain, defect chemistry, crystallinity, and diffusion at interfaces, which incorporate increasing chemical, structural, polar, and bonding contrast. 5. Understanding defects in the vicinity of interfaces Advanced materials span a continuum from passive to functional behavior. Modern technologies for energy, Table 1. Workshop participants Gregory S. Rohrer Carnegie Mellon University Mario Affatigato Coe College Monika Backhaus Corning Incorporated Rajendra K. Bordia University of Washington (now with Clemson University) Helen M. Chan Lehigh University Stefano Curtarolo Duke University Alex Demkov The University of Texas at Austin James N. Eckstein University of Illinois Katherine T. Faber Northwestern University Javier E. Garay University of California, Riverside Yury Gogotsi Drexel University Liping Huang Rensselaer Polytechnic Institute Linda E. Jones Alfred University Sergei V. Kalinin Oak Ridge National Laboratory Robert J. Lad University of Maine Carlos G. Levi University of California, Santa Barbara Jeremy Levy University of Pittsburgh Jon-Paul Maria North Carolina State University Louis Mattos Jr. The Coca-Cola Company Alexandra Navrotsky University of California, Davis Nina Orlovskaya University of Central Florida Carlo Pantano Pennsylvania State University Jonathan F. Stebbins Stanford University T. S. Sudarshan Materials Modification Inc. Toshihiko Tani Toyota Technological Institute K. Scott Weil Pacific Northwest National Laboratory 30 www.ceramics.org | American Ceramic Society Bulletin, Vol. 92, No. 6 (Credit: ACerS.)


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