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sustainability, and miniaturization will require a departure from the tailoring of continuously varying properties to engineered multifunctionality—technology demands will not usually be met by single-phase materials. For example, energy storage technologies need solid electrolytes offering 10 times higher ionic conductivities, energy harvesters need thermoelectrics that decouple phonon and electron transport, solid oxide fuel cells need to operate at much lower temperatures, and filtration technologies need materials with graded nanoporosity, chemically active surfaces, and environmental stability. The challenge is to extend defect chemistry models to account for the metastability of defect distributions in nanoheterogeneous ceramic systems where surfaces and interfaces are closely spaced. Models for defect distributions in these conditions also must account for the composition of the gaseous environment, high pressure and temperature, and high strain (often present in heterostructures), and high electric fields. To meet this challenge, a new defect chemistry perspective is needed that merges controlled-atmosphere surface science (as opposed to ultrahigh vacuum) with thermodynamic and kinetic models for defect formation. 6. Control of ceramics far from equilibrium Advances in processing methods during the past decade have freed ceramic science from the “tyranny of equilibrium.” We can synthesize ceramic materials that do not represent the state of lowest free energy but that persist, sometimes to surprisingly high temperatures, and can be fabricated and used in a variety of applications. The challenge is to understand and predict how the thermodynamic, physical, structural, and functional properties of materials prepared far from equilibrium differ from those of the bulk equilibrium phases and how these properties change with composition and grain size. This understanding is a prerequisite to tailoring materials for specific applications and to using concepts such as “inverse design” to find optimum materials for a given application. It also is a prerequisite to understanding when such materials have acceptable lifetimes in application and when they evolve to other states that often compromise function. 7. Accelerating the development of new ceramic materials Although there exists a wide range of synthetic paths for new ceramics, we are not yet able to make new materials in a sensible and systematic fashion and to explore the physical properties of such materials with an eye to unique behavior and novel applications. The goal is to create totally new types of ceramics rather than to modify existing ones by small changes in composition or processing. This area is especially fruitful for materials containing B, N, C, chalcogenides, and halides, which have not been explored as thoroughly as oxides. Addressing this challenge will require guidance from computation on target compositions and synthesis strategies as well as a merging of the practices of the synthetic chemist and ceramist. The challenge is to use available synthetic capabilities to make new materials in a sensible and systematic fashion and to explore the physical properties of such materials with an eye to unique behavior and novel applications. This brings the synthetic chemist and ceramist together, especially when complex organometallic precursors are used or when inorganic materials are functionalized with organic groups. 8. Intermediate-range order in glasses to enable novel properties Even though glass has been known since ancient civilizations, understanding and controlling the intermediate-range order in glasses remains a grand challenge. Intermediate-range order (IRO), meaning nonrandom structure beyond the first two or three coordination shells, is a long-standing problem in glasses and glass-forming liquids. Intermediate-range order influences diffusion and corrosion of glass surfaces, and thus strength and fracture toughness. The elucidation of IRO will have an immediate impact on the transport properties of many glass families. For example, the channel model for alkali silicates changes dramatically our approach to understanding diffusion of ions into or out of the bulk. Because many disordered solids are far from their equilibrium states, the development of order on cooling or disorder on heating is inherently dynamic, and it is often best studied by in-situ, high temperature methods. Such experiments are often technically challenging and need further development. Theoretical and computational developments could lead to major breakthroughs in interpreting structural data and understanding fundamental dynamic processes. In-situ structural measurements also are especially useful for testing and validating models (e.g., molecular dynamics), for which computational limits restrict the range of real temperatures that can be simulated accurately. Acknowledgement National Science Foundation Grant DMR-1216415 supported the workshop and report. The workshop organizers appreciate the encouragement and guidance of Lynnette Madsen. About the author Gregory S. Rohrer is W.W. Mullins Professor and head of the Department of Materials Science and Engineering at Carnegie Mellon University, Pittsburgh, Pa. Contact: gr20@andrew.cmu.edu. References 1G. S. Rohrer, M. Affatigato, M. Backhaus, R. K. Bordia, H. M. Chan, S. Curtarolo, A. Demkov, J. N. Eckstein, K. T. Faber, J. E. Garay, Y. Gogotsi, L. P. Huang, L. E. Jones, S. V. Kalinin, R. J. Lad, C. G. Levi, J. Levy, J. P. Maria, L. Mattos, A. Navrotsky, N. Orlovskaya, C. Pantano, J. F. Stebbins, T. S. Sudarshan, T. Tani, and K. S. Weil, “Challenges in ceramic science: A report from the workshop on emerging research areas in ceramic science,” J. Am. Ceram. Soc., 95 12 3699–712 (2012). 2K. Niihara, T. Ohji, and Y. Sakka, “3rd International Congress on Ceramics (icc3)”; p. 1001 in IOP Conference Series, Vol. 18, 2011. 3Y. M. Chiang and K. Jakus, “Fundamental research needs in ceramics: Report from the 1997 NSF workshop.,” http://www-unix.ecs. umass.edu/~jakus/nsf/nsf.ceramics.report6. pdf. n American Ceramic Society Bulletin, Vol. 92, No. 6 | www.ceramics.org 31


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