# The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop

Katherine T. Faber, Tewodros Asefa, Monika Backhaus-Ricoult, Richard Brow, Julia Y. Chan, Shen Dillon, William G. Fahrenholtz, Michael W. Finnis, Javier E. Garay, R. Edwin García, et al.

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## To cite this version:

Katherine T. Faber, Tewodros Asefa, Monika Backhaus-Ricoult, Richard Brow, Julia Y. Chan, et al. The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop. Journal of the American Ceramic Society, 2017, 100 (5), pp.1777 - 1803. 10.1111/jace.14881. hal-01685715

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FEATURE ARTICLE

# The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop

Katherine T. Faber<fnref n="1" /> ID | Tewodros Asefa<fnref n="2" /> | Monika Backhaus-Ricoult<fnref n="3" /> | Richard Brow<fnref n="4" /> |
Julia Y. Chan<fnref n="5" /> | Shen Dillon<fnref n="6" /> | William G. Fahrenholtz<fnref n="4" /> ID | Michael W. Finnis<fnref n="7" /> | Javier
E. Garay<fnref n="8" /> | R. Edwin García<fnref n="9" /> | Yury Gogotsi<fnref n="10" /> | Sossina M. Haile<fnref n="11" /> | John Halloran<fnref n="12" /> |
Juejun Hu<fnref n="13" /> | Liping Huang<fnref n="14" /> | Steven D. Jacobsen<fnref n="15" /> | Edgar Lara-Curzio<fnref n="16" /> |
James LeBeau<fnref n="17" /> | William E. Lee<fnref n="7" /> | Carlos G. Levi<fnref n="18" /> | Igor Levin<fnref n="19" /> | Jennifer
A. Lewis<fnref n="20" /> | Don M. Lipkin<fnref n="21" /> | Kathy Lu²² | Jian Luo²³ | Jon-Paul Maria<fnref n="17" /> | Lane
W. Martin²⁴ | Steve Martin²⁵ | Gary Messing²⁶ | Alexandra Navrotsky²⁷ | Nitin
P. Padture²⁸ ID | Clive Randall²⁶ ID | Gregory S. Rohrer²⁹ | Anatoly Rosenflanz³⁰ | Tobias
A. Schaedler³¹ | Darrell G. Schlom³² | Alp Sehirlioglu³³ | Adam J. Stevenson³⁴ |
Toshihiko Tani³⁵ | Veena Tikare³⁶ | Susan Trolier-McKinstry²⁶ |
Hong Wang³⁷ ID | Bilge Yildiz<fnref n="13" />,³⁸

<footnote n="1">¹Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California</footnote>

<footnote n="2">²Department of Chemistry and Chemical Biology & Department of Chemistry and Biochemical Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey</footnote>

<footnote n="3">³Corning Incorporated, Crystalline Materials Research, Corning, New York</footnote>

<footnote n="4">⁴Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, Missouri</footnote>

<footnote n="5">⁵Department of Chemistry, University of Texas, Dallas, Texas</footnote>

<footnote n="6">⁶Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois</footnote>

<footnote n="7">⁷Department of Materials, Imperial College, London, UK</footnote>

<footnote n="8">⁸Department of Mechanical and Aerospace Engineering, University of California San Diego, San Diego, California</footnote>

<footnote n="9">⁹School of Materials Engineering, Purdue University, West Lafayette, Indiana</footnote>

<footnote n="10">¹⁰Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania</footnote>

<footnote n="11">¹¹Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois</footnote>

<footnote n="12">¹²Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan</footnote>

<footnote n="13">¹³Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts</footnote>

<footnote n="14">¹⁴Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York</footnote>

<footnote n="15">¹⁵Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois</footnote>

<footnote n="16">¹⁶High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee</footnote>

<footnote n="17">¹⁷Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina</footnote>

<footnote n="18">¹⁸Materials Department, University of California, Santa Barbara, Santa Barbara, California</footnote>

<footnote n="19">¹⁹Materials Measurement Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland</footnote>

<footnote n="20">²⁰John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts</footnote>

<footnote n="21">²¹GE Global Research, General Electric, Niskayuna, New York</footnote>

<footnote>This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.</footnote>

<footnote>© 2017 The Authors. *Journal of the American Ceramic Society* published by Wiley Periodicals, Inc. on behalf of American Ceramic Society (ACERS).</footnote>
<sup>22</sup>Department of Materials Science and Engineering, VirginiaTech, Blacksburg, Virginia

<sup>23</sup>Department of NanoEngineering, University of California San Diego, San Diego, California

<sup>24</sup>Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California

<sup>25</sup>Department of Materials Science and Engineering, Iowa State University, Ames, Iowa

<sup>26</sup>Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania

<sup>27</sup>Department of Chemical Engineering and Materials Science, University of California Davis, Davis, California

<sup>28</sup>School of Engineering, Brown University, Providence, Rhode Island

<sup>29</sup>Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania

<sup>30</sup>M, Corporate Research Materials Laboratory, St. Paul, Minnesota

<sup>31</sup>HRL Laboratories, Malibu, California

<sup>32</sup>Department of Materials Science and Engineering, Cornell University, Ithaca, New York

<sup>33</sup>Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio

<sup>34</sup>Laboratoire de Synthèse et Fonctionnalisation des Céramiques, UMR3080 CNRS/Saint-Gobain, Saint-Gobain CREE, Cavaillon, France

<sup>35</sup>Toyota Central R&D Labs, Inc., Aichi, Japan

<sup>36</sup>Sandia National Laboratories, Albuquerque, New Mexico

<sup>37</sup>State Key Laboratory for Mechanical Behavior of Materials & School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an, China

<sup>38</sup>Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts

**Correspondence**

Katherine T. Faber, Division of
Engineering and Applied Science,
California Institute of Technology,
Pasadena, CA

Email: ktfaber@caltech.edu

**Funding information**

Division of Materials Research, Grant/
Award Number: 1619666

**Abstract**

Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under extreme conditions; and Rational design of functional glasses guided by predictive modeling. It is anticipated that these challenges, once met, will promote basic understanding and ultimately enable advancements within multiple sectors, including energy, environment, manufacturing, security, and health care.

**KEYWORDS**

defects, glass, layered ceramics, processing, ultrahigh-temperature ceramics

**1 | INTRODUCTION**

Given the ever-increasing pace of innovation in the 21st century, the U.S. National Science Foundation (NSF) sponsored a workshop, held in September 2016, to identify emerging research areas in ceramic and glass science. The meeting brought together 42 researchers in glass and ceramic materials from the United States and abroad to share both their expertise and vision in defining outstanding materials challenges. Participants from academia, industry,

and national laboratories were chosen to represent four material classes: amorphous materials, oxides, nonoxides, and composites. In preparation for the meeting, participants suggested topics for consideration. From these ideas, the workshop co-organizers, Katherine Faber, Jennifer Lewis, Clive Randall, and Gregory Rohrer, defined five themes for discussion: Ceramic Processing Science, Defect-Enabled Phenomena, Low-Dimensional Phenomena, Ceramics for Extreme Environments, and Glasses and High-Entropy Materials. These topics formed the basis of workshop
presentations and breakout discussions in which challenges were formulated and shared with the entire workshop attendance. In addition, strategies of data mining were explored as a tool for identifying new areas of study and opportunities for crosscutting research.¹

NSF had sponsored two prior workshops to identify and accelerate emerging research strategies in ceramics. The first assembly, “Future Research Needs in Ceramics,” co-organized by Yet-Ming Chiang and Karl Jakus, was held at NSF headquarters in June 1997.² More recently, a workshop chaired by Gregory Rohrer and held in March 2012, highlighted eight challenges for the ceramic and glass communities in its report, “Challenges in Ceramic Science: A Report from the Workshop on Emerging Research Areas in Ceramic Science.”³ Although less than 5 years elapsed since the previous meeting, it is well established that materials development cycles are shortening. This is frequently described in graphs of accelerating waves of innovation, first noted by economist Joseph Schumpeter. This notion gained popularity in publications like *The Economist*,⁴ where the six waves of innovation since the Industrial Revolution are depicted, each with decreasing period, but with increasing amplitude meant to imply greater complexity of innovation.⁵ The sixth and current wave includes sustainability, biomimicry, renewable energy, and green nanotechnology, all of which rely on materials innovation.

Reported here are eight challenges reached by consensus during workshop discussions, each describing the fundamental science required to forward basic understanding of ceramics and glasses and enable advances in, among others, energy, environment, manufacturing, security, and health care:

1. Ceramic processing: Programmable design and assembly

2. The defect genome: Understanding, characterizing, and predicting defects across time and length scales

3. Functionalizing defects for unprecedented properties

4. Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics

5. Ceramics in the extreme: Discovery and design strategies

6. Ceramics in the extreme: Behavior of multimaterial systems

7. Understanding and exploiting glasses and melts under extreme conditions

8. Rational design of functional glasses guided by predictive modeling

A common thread through these challenges is the importance of computational materials science through efforts such as integrated computational materials engineering

(ICME)⁶ for the design of new ceramic materials and prediction of properties. Examples of the design of complex oxides for electronic devices⁷ and superionic conductors⁸ provide evidence of advancements in the field. However, the use of these techniques for highly defective structures, ultrahigh-temperature materials, or complex, multicomponent amorphous materials is sparse. A second overarching need is the advancement of probes necessary to characterize and visualize materials at smaller length scales, for example, a single atomic defect, and at higher temperatures and pressures, for example, at T>2000°C. Each challenge is described in detail below following the reports of the five subgroups.

## 2 | CERAMICS PROCESSING SCIENCE

The ability to programmably design and assemble ceramics would enable unprecedented mechanical, electrical, thermal, and other properties. Several novel routes have emerged for precisely controlling the composition and structure of ceramics over multiple length scales, including guided colloidal assembly⁹⁻¹⁸ and 3D printing methods.¹⁹⁻³⁷ When those are combined with techniques, such as atomic layer deposition and “cold sintering,” ceramics can be seamlessly integrated with polymers (or metals) that melt at low temperatures. A new ceramics processing paradigm that links multiscale modeling with computer-aided design and assembly is needed to fully exploit the broadening palette of materials, architectures, and fabrication strategies.

### 2.1 | Challenge #1: Ceramic processing: Programmable design and assembly

Ceramics processing methods uniquely involve several states of matter: dry powders, colloidal suspensions and gels, green and sintered bodies. Unfortunately, the constitutive behavior of each of these states is imperfectly known. Multiscale modeling to optimize material composition, microstructure, and topology coupled with the ability to re-alize those designs, offer the potential to create ceramic-based constructs with extraordinary performance. Modeling and simulation research must be directed toward understanding the transformation of initial building blocks, both colloidal particles and other constituents, into sintered bodies that give rise to the properties of interest.

Multiscale modeling spans length scales ranging from atomistic to the mesoscale. Density functional theory (DFT) electronic structure calculations have received considerable attention as part of the Materials Genome Initiative with the aim of discovering new ceramics and their properties.³⁸,³⁹ DFT can be used to generate quantum-
accurate potentials for atomic scale simulations,<sup>40,41</sup> to model interfacial structure, energies, and the stability of nanoscale features. New automated techniques can generate accurate potentials when combined with DFT methods, and inform the design of the complex interfaces that are anticipated with the advanced architectures of heterogeneous materials.<sup>42-44</sup> They can also provide mechanistic understanding of materials processes such as diffusion, interface mobilities, and phase transitions. Mesoscale modeling, predominantly phase field<sup>45</sup> and Potts kinetic Monte Carlo models,<sup>46</sup> can treat microstructure and its evolution at processing temperatures of interest under different energy fields when applicable. However, models to assess engineering properties from ceramic microstructures are immature, as they typically have to incorporate the variation in microstructural features, making for very large simulations, or need to combine simulations spanning multiple scales, requiring new methods to couple models at different length scales.<sup>47,48</sup> To programmably generate ceramic-based architectures with optimized composition and structure across multiple length scales, one must know *what features are desirable and then use this input to deterministically guide the assembly process*.

By harnessing forces ranging from weak van der Waals to external electromagnetic fields, one can guide colloidal self-assembly in two and three dimensions to create novel architectures with as yet unexplored properties. Two-dimensional assembly of nanosheets into superlattice structures guided by van der Waals forces yield completely new architectures and material combinations.<sup>9,10</sup> DNA-coated particles<sup>11,12</sup> and Janus rods coated with hydrophobic patches form “atom-like” building blocks<sup>13</sup> that can be assembled into 3D architectures (Figure 1). Photoresonant dispersants enable creation of colloidal suspensions that can be switched on demand from a fluid to gel state upon exposure to UV light.<sup>14</sup> With further synthetic advances, new classes of shape and chemically anisotropic

particles with engineered interactions that guide self-assembly can be realized.

Beyond those strategies, external fields are also being exploited to guide colloidal assembly. For example, electric fields applied to colloid dispersions can structure particles by electrophoresis and dielectrophoresis.<sup>15,16</sup> Magnetic fields can be used to orient ferroelectric particles for templated grain growth.<sup>17</sup> Importantly, even diamagnetic colloidal particles can be oriented under very high magnetic fields to produce textured ceramics.<sup>18</sup> However, to harness external fields to locally “write microstructure” in a predictive manner, a deeper understanding must be developed of how particle dynamics, structure, and assembly are influenced by applied external fields both in the absence and within complex molds that define their final shape. With these capabilities in hand, new classes of crystallographically tailored, polycrystalline ceramics that exhibit single crystal-like properties could be realized in a highly scalable manner.

Additive manufacturing methods, such as robocasting<sup>19-21</sup> or stereolithography,<sup>22-27</sup> enable patterning of concentrated colloidal suspensions and photopolymerizable resins. For example, robocasting, also known as direct ink writing, has been used to produce lithium ion microbatteries composed of high aspect ratio, interdigited electrodes<sup>28</sup> (Figure 1), as well as 3D periodic lattices.<sup>21</sup> New advances in colloidal suspension design, such as biphasic mixtures composed of attractive and repulsive colloidal particles,<sup>29</sup> coupled with the implementation of active mixing and switching microfluidic printheads,<sup>30,31</sup> would further accelerate the compositional and architectural complexity realizable by this technique.

New cellular ceramics can be fabricated by light-based 3D printing of preceramic monomers, nanoparticle-filled or pure resins.<sup>22-27</sup> For example, nonoxide cellular ceramics that are virtually pore free are produced by patterning a preceramic monomer resin using stereolithography followed by high-temperature pyrolysis (Figure 1).<sup>22</sup> However,

<figure><img src="image_4.png" /><figcaption>**FIGURE 1** Recent advances in ceramics processing science. From left to right: Optical image of the guided self-assembly of colloidal SiO₂ rods (~2.2 µm in length and 1.1 µm in diameter) coated on one end with a hydrophobic metallized tip (black) [inset: tetrahedral “atom-like” cluster composed of four rods.]<sup>13</sup> (reprinted with permission, American Chemical Society); Optical image of a lithium ion microbattery composed of 3D printed, interdigited cathode (LFP, dark) and anode (LTO, white) high aspect ratio features<sup>28</sup> (reprinted with permission, Wiley); SiOC microlattice fabricated by stereolithography of a preceramic monomer solution; and multilayer thermoelectric device obtained by cold sintering at 250°C that integrates n-type ZnO, p-type Ca₃Co₄O₉, and polytetrafluoroethylene, a thermoplastic insulating material</figcaption></figure>
fundamental challenges remain to both understand and optimize the pyrolysis process to enable incorporation of fibers or active fillers within these printed architectures. Nanoparticle-filled and pure polymer structures in the form of octet trusses and other novel geometries have recently been constructed by these methods.²⁵,²⁷ In the latter case, the structures serve as sacrificial templates, which are coated with a thin layer of Al₂O₃, SiO₂, or other materials via processes such as atomic layer deposition (ALD) or chemical vapor deposition (CVD) prior to template removal to achieve cellular ceramics with exceptional strength and stiffness at ultralow densities.²⁴⁻²⁷,³² This approach essentially allows one to transform 2D thin “films” into 3D cellular materials. While considerable research has been carried out to understand the structure-property relations of thin film ceramics, the mechanical properties of *freestanding* 3D “film-based” architectures require rigorous study.

The densification of ceramics by high-temperature sintering has been the status quo for millennia. Recently, a new paradigm for sintering has been introduced, known as *cold sintering*.³⁴⁻³⁶ It is now possible to densify ceramic green bodies at temperatures as low as 25°C to 300°C via a transient liquid phase (eg, water). This nascent method offers the potential to heterogeneously integrate ceramics with disparate materials that would otherwise melt, decompose, or react, including ceramic-polymer (Figure 1) and ceramic-metal composites. To date, new dielectric materials, ionic electrolytes, and semiconducting composites and multilayers have been densified by cold sintering.³⁴⁻³⁶ However, despite its significant promise, little is known about the fundamental mechanisms and limitations of this new approach.

The major progress in colloidal science, guided self-assembly, coating methods, and 3D printing, coupled with cold sintering, offers new opportunities to design and integrate dissimilar materials that were previously unimaginable. By establishing a new ceramics processing paradigm, new materials will be created with unique combinations of matter, architecture, and properties that require fewer trade-offs. For example, it is well-known that important functional and structural properties of porous materials are inversely related,³⁷ that is, their permeability, specific surface area, and corrosion rates tend to increase with increasing porosity, while their strength, creep resistance, and thermal conductivity decrease. The ability to optimize the topology and programmably fabricate multifunctional porous ceramics that combine both high strength and permeability would impact a myriad of applications, including anode-supported fuel cells and asymmetric oxygen-separation membranes. Limiting barriers imposed by similar property trade-offs that exist across the spectrum of ceramic applications may also be overcome by this approach with appropriate transition and linkage to manufacturing engineering.

### 3 | DEFECT-ENABLED PHENOMENA

A defect in a material is most commonly defined as a disruption to the periodicity of its crystalline organization, that is, a structural anomaly, or to its composition, that is, chemical irregularity. As compared to metals and semiconductors, defects in ceramics are distinguished by the additional constraints and levers of electrostatics: global charge neutrality must be preserved in the bulk.⁴⁹,⁵⁰ Structural anomalies have long played defining roles in the properties of ceramics and, in many cases, have been enabled through electrostatic considerations. In the most generalized view, point defects (eg, vacancies, interstitials) determine transport characteristics; linear defects (dislocations) establish strain relaxation behavior; planar defects (eg, domain and grain boundaries) govern ferroelastic, piezoelectric, and ferroelectric response; and volume defects (eg, secondary phases) regulate mechanical properties. Moreover, not only is the physical dimensionality of the defect relevant to its function, but also factors such as defect concentration, association configurations, and dissociation interactions, length scale, and even time scale of interaction are critically important to the macroscopic material behavior. Thus, structural anomalies in ceramics exist over a complex, multidimensional space (Figure 2), and from these, opportunities emerge for precise control of material properties in both highly studied and largely overlooked regions of this space.

In this context, two challenges emerge. The first is to understand, characterize, and predict defect populations and distributions in ceramics as they exist within the phase space of Figure 2. Given the fact that defects can perturb properties over orders of magnitude, success here will lead to the emergence of a “defect genome,” which will complement the materials genome for comprehensive materials design. A second challenge is to go beyond the passive characterization of defects and move to their controlled creation and toward the functionalization of these defects. This may be achieved in particular through the control of defect-defect interactions. Such defect functionalization is expected to yield materials with unprecedented response to applied stimuli, including electrical, magnetic, or optical drivers. To address both challenges, advances in defect visualization and direct characterization arise as a pressing need.

#### 3.1 | Challenge #2: The defect genome: Understanding, characterizing, and predicting defects across time and length scales

Many of the desirable functional properties of ceramics depend on defect populations and their character. New classes of ceramic materials are envisioned, from those containing very few, precisely located, isolated anomalies to others containing extremely large defect densities that,
<figure><img src="image_5.png" /><figcaption>**FIGURE 2** Defects are critical for ceramic applications. From point⁹⁸,⁹⁹ to planar¹⁰⁰,¹⁰¹ to bulk¹⁰² defects, modern ceramic systems rely upon exacting and careful control of these features to ensure operation and performance in applications.¹⁰³⁻¹⁰⁷ Looking toward the future, deterministic control of these defects and even formation of designed mesostructures based on defects are expected to enable new phenomena and better performance. From top left to right: STM images of the c(4×2) reconstructed surface of SrTiO₃⁹⁸ (reprinted with permission, Elsevier); an HRTEM image of dislocation loops in a high-temperature irradiated SrTiO₃ crystal⁹⁹ (reprinted with permission, Elsevier); bright-field STEM image of a Sr₇Ti₆O₁₉ epitaxial film grown on (110) DyScO₃¹⁰⁰ (reprinted with permission, Nature Publishing Group); SEM micrograph of an interface delamination crack for 8% Y₂O₃ partially stabilized ZrO₂ thermal barrier ceramic coating on NiCrAlY subjected to six thermal fatigue cycles¹⁰¹ (reprinted with permission, ASME); local thermal dielectric breakdown events (dark spots) linked to mechanical breakdown events in a piezoelectric film. From bottom left to right: Fuel cells¹⁰³ (reprinted with permission from Forschungszentrum Jülich); Memristor¹⁰⁴ (reprinted with permission from HP); Cellular Technology;¹⁰⁵ Barrier Coatings;¹⁰⁶ Electron Gun¹⁰⁷ (reprinted with permission from RBD Instruments, Inc.)</figcaption></figure>

for example, drive formation of unexpected, entropy-stabilized phases and associated emergent phenomena. Application of “stressors,” either during or after synthesis, will generate dynamic defect response that can be further manipulated for material design and property control.

In the following, a few examples illustrate critical needs to fully exploit the capabilities of current ceramics and point to new challenges in recently discovered ceramics.

Existing, simple point defect chemistry models (see textbooks⁴⁹,⁵⁰) rapidly reach their limits when confronted with high defect concentrations, strong defect interactions,⁵¹ dislocations,⁵²,⁵³ or interfaces.⁵⁴ Similarly, difficulties are encountered when trying to discern defect behavior far from thermodynamic equilibrium or under complex configurations of thermal gradient, stress, electrical field, or magnetic field. In most cases, point defect thermodynamic models have not yet been sufficiently developed. In the past, the required system size has exceeded in size and/or complexity of the computational possibilities. Preliminary efforts have attempted to capture the interplay between antisite defects and phase formation,⁵⁵ and between electrical field, stress, and defect distribution.⁵⁶ Further efforts in this direction are needed, especially those targeting dynamic system response.⁵⁷

Interaction and motion of higher dimensionality defects remain a challenge for predictive modeling and for phenomenological description. Even though motion of domain walls in ferroelectrics has been known for many years, the

relevant processes are poorly understood. Several key needs emerge: (i) developing a formalism that describes long range electromechanical coupling in polycrystalline ceramics,⁵⁸ including grain-to-grain and domain-to-domain coupling, (ii) enabling the theoretical framework for experimental data sets that describes the interaction of dynamic domain walls with pinning sites and various types of grain boundaries⁵⁹ and explains cascaded motion of domain walls,⁶⁰ (iii) establishing processes to reliably turn domain wall motion on and off in ferroelectric materials to optimize figures of merit for particular applications, (iv) making progress toward controlled processing/generation of defect concentrations in films,⁶¹ (v) characterizing the role of defects on properties across multiple length scales.

Mixed-oxide materials with configurational disorder made by populating a single sublattice with a variety of different cations have been found to exhibit unexpected crystal symmetry and high material stability.⁶² This structural and chemical complexity, in which multiple types of metal cations are “stuffed” into a structure, creates a highly defective, engineered material and a potential route to exceptional properties. In some cases, the resulting oxides display extremely delayed phase transitions and melting. Existing frameworks for understanding the stability of such ceramics are largely based on ionic size and charge approaches; first principles calculations would build fundamental understanding and enable the synthesis of designed materials.
Progress in modern thin film growth and control of growth processes has ushered in an era in which materials can be synthesized from the bottom up, using various designed building blocks, for example, atomic layers, bilayers, or block units. It is generally assumed that the individual building block chemistry and the global architecture determine the final material properties, and in many cases, little attention is paid to defects and their interactions. Several efforts have leveraged synthesis by design in recent years, for example, 3D thermoelectric materials that use building blocks to decouple electric and phonon conduction,⁶³⁻⁶⁵ memristive switches that gain their functionality from localized reversible, reproducible redox reactions,⁶⁶,⁶⁷ and emergent devices with 2D interfacial properties in layered structures.⁶⁸⁻⁷¹ For each of these examples, an implicit control of defect structure is supporting or even driving the desired effects. Embracing these considerations for assembled structures, including defect engineering as an additional design parameter, processing tunable defect structures will open access to a new range of materials and phenomena. So far, these approaches remain relatively underdeveloped; however, there is potential for considerable progress, if defects can be harnessed in this manner.⁷² Key challenges and opportunities go beyond traditional chemical synthesis and focus either on establishing the desired defects in situ during the synthesis⁷³ or controlling ex situ the production of specific defect types and densities at selected sites.⁷⁴,⁷⁵ For controlled thin film synthesis, questions arise about the possibility of using the Vegard strains that result from defect production during film growth to induce changes locally in the lattice and in the associated local properties.⁷⁶,⁷⁷

Interface defect chemistry changes in response to “stresseurs” from the environment, including elevated temperatures, gas pressure, electrochemical potential, electric field, and mechanical stress. Experimental and modeling efforts have started to develop formalisms for the defect structure and chemistry of (2D) grain boundaries, surfaces, and interfaces, and have captured surface and grain-boundary reconstruction in thermodynamic equilibrium situations.⁷⁸ Improved understanding of dynamic interfaces, such as oxygen exchanging electrodes⁷⁹,⁸⁰ or oxide catalysts supporting chemical synthesis, has been gained by operando imaging and spectroscopy⁸¹ and supported by simple models.⁸² However, to date it has not been possible to fully model these highly driven systems due to their size, complexity, and intricate boundary conditions. More extended predictive simulation of oxide interfaces under complex drivers and at extended spatial and time scales requires further progress in computing, including both higher performance supercomputers and novel computational methods to extend time scales⁸³ and spatial scales⁸⁴ to the ranges that address interface behavior and its evolution.

Progress in computational tools is expected to enable better prediction and help to build fundamental understanding of dynamic interfaces under various stressors and for various technologies.

Li- or Na-ion conducting solid electrolytes for battery applications have significant advantages over liquid electrolytes, such as higher stability, higher transference numbers, and lack of dendrite formation.⁸⁵ While a framework for tuning and optimizing the defect chemistry is available for crystalline electrolytes, it is not the case for ionic conducting glasses, where understanding of order and its evolution are missing. On the other hand, noncrystalline electrolytes generally display higher conductivity than their crystalline counterparts. This contradictory situation suggests that extending the understanding of glassy electrolytes, likely through atomistic level simulations, may provide tremendous payoff in both classes of conductors. Such understanding may even encourage the consideration of new classes of materials, such as composite systems or partially crystalline glasses.

Low-temperature ceramics synthesis approaches, as highlighted in Challenge #1, have been reported that use “fluxes” and drive dissolution/recrystallization-based densification at very low temperatures.³⁴⁻³⁶ It is not clear if the resulting ceramics have similar properties as those processed by high-temperature sintering; it may be necessary to study in detail the nature of the defects introduced by “flux”-supported synthesis, understand the mechanisms, and extract possible levers.

Along with appropriate theoretical and computational techniques, the defect genome will complement the materials genome for comprehensive materials design. Computational capacity and speed have grown steadily over the past years. In addition, more and more multiscale approaches and parallel networking tools have been developed, which will soon allow treatment of larger and more complex systems and address the above opportunities.

## 3.2 | Challenge #3: Functionalizing defects for unprecedented properties

Although functionality of defects is exploited in materials, the idea of engineered functionalization with spatial and time resolution to drive homogeneous properties, as well as device capabilities, has received far less attention. Accordingly, fewer specific examples are available of how this approach can enhance materials performance. Nevertheless, some intriguing possibilities can be envisaged. For example, deep trap states in wide band gap dielectrics have been shown to reduce electrical losses under applied field excitation.⁸⁶ Can this approach be generalized such that defects become a source of material stability and functionality? Can benign defects be used to
trap deleterious ones? This would be a source of “engineered reliability.” Functionality may also arise via defect-defect interactions. For example, the motion of one defect could trigger the motion of many others, giving rise to cascaded motion. In another example, in this case already demonstrated, extended defects, such as hetero-interfaces or dislocations, can influence the distribution of point defects that can, in turn, alter local properties.⁸⁷ This type of emergent behavior would result in materials with exceptionally high response to the application of a given stimuli.

Defect-defect interactions further hold the potential for emergence of neuromorphic properties, resulting from the existence of multiple, reconfigurable interacting states. What kind of defect structures, if any, would lead to such properties, how would they be created, and how would the appropriate time and length scales for interaction be ensured? These are intriguing questions that arise when one recognizes defects as features that can be leveraged for accessing material behavior not possible via a static, periodic arrangement of atoms.

To achieve the goals outlined above, the development of a defect genome and the functionalization of defects as toolkits for materials design will require comprehensive understanding of relevant defect interactions, defect dynamics, and defect-property relations. Imaging and spectroscopy techniques essential for gaining this understanding have been tremendously improved over the past few years. In particular, in situ and operando direct defect analysis in realistic environments has been achieved in many settings. For example, aberration corrected (scanning) transmission electron microscopy (STEM) now provides accurate and precise quantification of atom positions directly in real space,⁸⁸,⁸⁹ the capability to count atoms by comparing experiment and theory⁹⁰ and the ability to map chemistry at the atomic scale with electron energy loss and X-ray spectroscopies.⁹¹ This progress allows direct identification and quantification of defects in terms of both their atomic and electronic structures.⁹² Furthermore, recent in situ (scanning) transmission electron microscopy and scanning tunneling microscopy (STM) techniques advances have enabled the direct tracking the material evolution as a function of time and environmental variables.⁹³ For example, surface reconstructions can be directly observed in cross-section by transmission electron microscopy (TEM) and atop surface by STM during heating or catalytic/electrochemical reactions.⁹⁴ At the same time, other techniques, such as high-resolution phase-resolved tomography, neutron scattering, nuclear magnetic resonance (NMR), electron spin resonance (ESR), Raman, infrared (IR), positron lifetime annihilation, and surface spectroscopies have also made tremendous strides in the past decade, some techniques even allowing operando observation.⁹⁵⁻⁹⁷ In combination, these new tools

offer opportunities to connect the behavior of defects in ceramics and their impact on properties across length and time scales.

## 4 | LOW-DIMENSIONAL PHENOMENA

Two-dimensional structures create opportunities—and challenges—that are distinct from one-dimensional or three-dimensional materials. In particular, their high anisotropy in mechanical, electrical, and transport properties lead to both novel scientific phenomena and unique functional and structural capabilities. The current scientific excitement about phenomena in exotic two-dimensional materials is exemplified by the 2016 Nobel Prize in physics (Thouless, Haldane, and Kosterlitz) that recognizes the use of concepts in topology to explain, among other things, phase and property transitions in two-dimensional materials. The materials that embody the current challenge span free-standing materials, surfaces, and supported layers, as well as materials confined at interfaces and grain boundaries, as illustrated in Figure 3. The challenge is to define structure-property relations for these materials.

### 4.1 | Challenge #4: Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics

It has been known for decades that it is possible to delaminate or exfoliate layered crystals into two-dimensional sheets a few atoms thick.¹¹¹ However, there has been a recent growth of research in this area and the range of materials available has grown enormously.¹¹² Among the ceramics that can be produced in single layer form are clays,¹¹³ hydroxides,¹¹⁴ oxides,¹¹⁵ h-BN,¹¹⁶ and transition-metal carbides.¹¹⁷ Most of these materials have a van der Waals gap between the separable layers. In some cases, the materials can be exfoliated in solution simply by sonication. In other cases, ions may be intercalated into the gap, increasing the separation of layers, and thereby reducing the strength of the bonding between layers, making exfoliation possible in appropriate solutions. When the bonding between the layers is stronger, it has also been shown that the layers can be separated by etching or protonation in strong acid.

The free-standing layers described above are produced at low temperature and are kinetically stable in this form. In addition, there are also spontaneously forming two-dimensional ceramic interfacial phases, which are called “complexions” to differentiate them from the three-dimensional bulk phases rigorously defined by Gibbs.¹¹⁸ These
**FIGURE 3** Schematic representations and micrographs of real two-dimensional ceramics. (A) Free-standing layer; (B) plan view TEM of single layer h-BN<sup>108</sup> (reprinted with permission, AAAS); (C) supported layer; (D) transverse TEM image of a vanadia layer on TiO<sub>2</sub><sup>109</sup>(reprinted with permission, AIP); (E) confined layer; and (F) TEM of grain-boundary complexion (Nd bilayer between alumina grains)<sup>110</sup> (reprinted with permission, Elsevier)

<figure><img src="image_6.png" /></figure>

complexions can form on free surfaces,<sup>119</sup> at grain boundaries,<sup>118</sup> and heterophase boundaries.<sup>120</sup> Among supported surface complexions, adsorbate-based surficial films,<sup>119</sup> reconstructions,<sup>121</sup> and controlled surface terminations are considered.<sup>122</sup> These two-dimensional materials can be thought of as thermodynamically stable nanoscale coatings or atomic-level surface modifications that can be controlled by changing the temperature or chemical potential of the constituents to alter the transport and catalytic properties.

The formation and control of grain-boundary complexions can be used to influence microstructure evolution during processing. Specifically, the recent discovery of grain-boundary phase-like behaviors has already provided new insights into several long-standing scientific mysteries that puzzled the ceramic community for decades, for example, the origins and atomistic mechanisms of solid-state activated sintering<sup>123</sup> and abnormal grain growth.<sup>124</sup> Beyond the interfacial diffusivity and mobility that govern the microstructural development, grain-boundary complexions often control properties of structural and functional ceramics, including—but not limited to—strength, toughness, creep resistance, electrical, thermal, and ionic conductivities, the nonlinear I-V character of varistors, and the critical current of superconductors.<sup>125</sup>

Two-dimensional ceramics possess characteristics that make them scientifically interesting and potentially useful.

For example, enhanced transport properties in two-dimensional ceramics can enable energy storage devices<sup>126,127</sup> and may play a role in cold sintering.<sup>128</sup> The rich catalytic properties of two-dimensional ceramics enable reactions that are important for the production and utilization of solar fuels.<sup>129</sup> Interface complexions, which have been shown to be thermodynamically stable, undergo transformations that control the evolution and properties of the microstructure. The properties are tunable by temperature, pressure, and chemistry, and may even be switchable by external fields. The recent demonstration that complexion transformation kinetics could be represented on conventional time-temperature-transformation diagrams opens up the possibility of establishing predictable control over the microstructural evolution of ceramics.<sup>130</sup> The next obvious step in advancing the science of two-dimensional ceramics is understanding structure-property relations. To date, it is not possible to predict how the properties of oxides only known to exist in the bulk state change when those oxides are made into nanometer thin sheets.<sup>131</sup> Similarly, predicting the properties of (both free-standing and confined) two-dimensional materials that have stoichiometries and structures that do not appear in the bulk is not feasible.<sup>117,118</sup>

Two-dimensional ceramic materials are ripe for investigation and discovery. For the past decade, there has been an intense focus on modeling two-dimensional systems,
including the two-dimensional electron gas at the LaAlO₃/
SrTiO₃ interface¹³² and graphene.¹³³ This foundation has
provided a wealth of experimental techniques for the syn-
thesis and characterization of two-dimensional materials. At
the same time, there has been a rapid growth in the discov-
ery of new two-dimensional ceramics¹¹²,¹¹⁷ that have not
been subjected to the same detailed studies as the model
systems. Therefore, there is an opportunity to adapt the
techniques used to study the model materials to a wide
range of new materials. Since this is a synthesis, process-
ing, and characterization problem, it fits more naturally in
the ceramics domain than any other. As a result of devel-
oping structure-property relationships for these materials, it
will be possible to identify new targets for synthesis.

The study of two-dimensional systems also presents
challenges and opportunities for modeling. Specifically, the
analysis of the atomistic stability of two-dimensional cera-
mic structures, including the calculation of the structure,
while incorporating intrinsic and extrinsic defects into the
formulation remains a challenge.¹³⁴ For example, the calcu-
lation of energies of formation for charged point defects
(while conserving the charge neutrality condition), energy
barriers for ionic diffusion, the impact of phonon-defect,
defect-defect, and photon-defect interactions, surface-atmo-
sphere or solution interactions, and their impact on the sta-
bility of two-dimensional ceramic structures is still done on
a case-by-case basis.¹³⁵,¹³⁶ In many instances, these calcu-
lations are not yet possible, particularly for cases where the
interface provides technologically relevant functionalities
such as ferroelectrics, thermoelectrics, rechargeable batter-
ies, and fuel cells. The rational integration of atomistic
results into meso- and continuum descriptions is not yet
possible and the formulation of descriptions to define their
two-dimensional equilibrium as a result of the abutting
three-dimensional phases is limited to only a few cases.¹³⁷
The formulation of automated theoretical and numerical
formalisms that guide the synthesis of tailored properties
for two-dimensional systems that parallel the development
of existing three-dimensional systems, such as the alloy
theoretic automated toolkit¹³⁸ and the atomic simulation
environment¹³⁹ at the atomic level, or OOF¹⁴⁰ and
MOOSE¹⁴¹ at the meso- or continuum scale, are not avail-
able. Therefore, there is a unique opportunity for the
ceramics community to develop multiscale two-dimensional
tools and platforms that will enable the rational and sys-
tematic exploration of these systems. Furthermore, uncer-
tainty quantification of two-dimensional systems that are
able to assess the impact of average and extremal events is
nonexistent, even though numerical tools such as Dakota¹⁴²
are emerging and can provide the context to understand
their impact.

Energy storage is already an important part of ceramics
research and is likely to increase in activity considering that

the industry forecasts that by 2019 the market will be as large
as US $120B. Ceramic materials are key performance-deter-
mining constituents of Li-ion batteries,¹⁴³ pseudocapaci-
tors,¹²⁷ and hybrid devices for energy storage.¹⁴⁴ The two-
dimensional materials already mentioned have the potential to
enable the next generation of thin and flexible rechargeable
batteries with improved storage capability, faster charging
rates, safer operation, and a longer lifetime. While graphene
has been extensively studied, much less is known about struc-
ture-property relations in two-dimensional ceramics.¹⁴⁵ Fast
intercalation of not only lithium, but also sodium, potassium,
and multivalent ions (aluminum or magnesium) into elec-
trodes built of free-standing two-dimensional ceramic
nanosheets may lead to improved batteries. Additionally, two-
dimensional ceramics may dramatically expand the range of
solutions for automotive power systems and the large-scale
stationary storage of renewable energy, once they can be pro-
duced in large quantities. Also, emerging energy storage
devices entirely based on solid-state (ceramic) technology are
currently limited by the structure and properties of the two-
dimensional heterointerfaces through which they are spatially
coupled. Thus, a fundamental understanding of interface
stability and transport properties is the first step to remove
existing performance bottlenecks.

Two-dimensional ceramic materials will also impact chal-
lenging yet important problems related to catalysis. These
materials have the right structural features to serve as cata-
lysts for the most important reactions in energy conversion
systems. They are also among the most promising con-
tenders for fundamental studies of the electrochemical and
photochemical properties of materials. Their unique proper-
ties provide catalytically rich surfaces for reactions pertinent
to renewable energy applications, such as the hydrogen evo-
lution reaction and the oxygen evolution reaction.¹²⁹,¹⁴⁶
Many of them have also been shown to catalyze the oxygen
reduction reaction in fuel cells, assisting in the generation of
energy from green energy carriers such as hydrogen. These
unique attributes, coupled with the many strategies available
to produce them with numerous structures and compositions,
as well as their tunable electronic, surface, and defect prop-
erties, make two-dimensional ceramics valuable in the search
for sustainable energy resources.

In summary, the recent discovery of many two-
dimensional structures has outpaced the understanding of
their properties. Establishing an understanding of struc-
ture-property-processing relations for two-dimensional
structures is expected to lead to easily tunable properties
through small changes in chemistry, processing, or exter-
nal fields. These two-dimensional structures may have
impact on energy applications (batteries, supercapacitors,
catalytic materials), miniaturization of switching devices,
low energy computing, and novel functional and mechani-
cal properties.
5 | CERAMICS FOR EXTREME ENVIRONMENTS

Attributes that make ceramics attractive for society's imper-
atives in energy, transportation, and national security
include their refractoriness, stability in chemically aggres-
sive and radiation environments, as well as a diverse range
of unique functional and mechanical properties, notwith-
standing their limited toughness. Nevertheless, societal
demands for continuing technological progress translate
into a relentless drive to further extend the capabilities of
ceramics into regimes of unprecedented severity. These
demands pose new challenges to the scientific understand-
ing of ceramic materials, and specifically, to the elucidation
of mechanisms that control their response in extreme envi-
ronments. Concomitantly, these demands motivate the dis-
covery and synthesis of new ceramics.

The performance limits of materials may be defined in
terms of (i) loss of functionality, such as resulting from a
phase transition with increasing temperature; (ii) loss of
shape or physical integrity under thermomechanical stresses
or applied fields, such as deformation or fracture; or (iii)
degradation of structure and properties over time, such as
creep rupture or radiation damage. Any situation that drives
known materials past their performance limits may be
defined as “extreme,” providing at once a series of techno-
logical challenges and an opportunity for fundamental
materials development. For the purposes of this discussion,
extreme environments are defined as those for which there
are no known materials solutions, wherein the motivation
for discovery is greatest, and where the theoretical and
experimental infrastructure to study and understand their
behavior is still inadequate. Extreme environments are fur-
ther exacerbated when more than one excessively harsh
condition is simultaneously involved.

Notable examples of technologically extreme environ-
ments driving scientific research in ceramics are illustrated
in Figure 4. These include:

(i) *Hypersonic flight*, where sharp leading edges are required in aircraft for reduced draft and improved maneuverability.¹⁵² Required temperatures are in excess of 2000°C,¹⁵³ with heat fluxes of multiple MW/m²,¹⁵⁴ which can translate into extreme thermal gradients and stresses. Ionization of the impinging air¹⁵⁵ enhances oxidation potential,¹⁵⁶ followed by catalytic recombination at the surface, leading to still further heating.¹⁵⁷ Ultrahigh-temperature ceramics (UHTCs)¹⁵⁸ and C<sub>f</sub>/SiC composites,¹⁵⁹ current candidate materials for these applications, are hindered by severe oxidation at the target temperatures.¹⁶⁰⁻¹⁶³

(ii) *Aerospace propulsion*, encompassing gas turbines,
scramjets, and rocket engines, with prospective gas tempera-
tures in excess of ~1700°C,¹⁶⁴ ~2000°C,¹⁵² and ~3000°C,¹⁵⁷
respectively. Gas turbines for aircraft propulsion and power

generation share common goals, namely increased efficiency
and reduced emissions, although aircraft engines presently
lack renewable or carbon-neutral alternatives. Target material
temperatures exceed 1500°C in near-sonic flows of combus-
tion gases at pressures of order 5 MPa (~50 atmospheres),
containing well over 6 vol% of water vapor as a combustion
product. Erosive/corrosive entrained debris that may impact
or deposit on component surfaces further exacerbates the
operating environment. All known turbine hot section
materials, whether metallic¹⁶⁵⁻¹⁶⁷ or the recently introduced
ceramic composites (CMCs),¹⁶⁴,¹⁶⁸ rely on ceramic coatings.
However, both the thermal barrier coatings (TBCs) used to
protect metallic components¹⁶⁴,¹⁶⁹ and the environmental
barrier coatings (EBCs) used to protect CMCs¹⁶⁴,¹⁷⁰ are
temperature limited when exposed to molten dusts, which
comprise highly corrosive calcium-magnesium aluminosili-
cates (CMAS).¹⁶⁴,¹⁷¹⁻¹⁷⁵ A second major barrier is associated
with coating toughness limitations,¹⁷¹ as the consequences of
coating loss become more critical with increasing reliance on
their continued protection. No present material meets both
the toughness and CMAS resistance requirements over the
relevant range of temperatures. Ceramics in hypersonic and
rocket propulsion operate in arguably mechanically simpler
environments, where the problems introduced by the rotation
of gas turbine components are largely absent, but heat fluxes
can be much more severe owing in part to the concepts
involving fuel cooling of the hot walls. Materials of the same
families considered for leading edges are of interest, but
subject to similar durability concerns due to the extreme
environments.

(iii) *Advanced nuclear energy*, where materials must withstand high fluxes of energetic particles.¹⁷⁶ While current and prospective next-generation fission reactors pose substantial challenges to ceramics, for example, as advanced fuels and wasteforms,¹⁷⁶ fusion reactors arguably represent one of the most ambitious challenges to the spectrum of extreme materials technology.¹⁷⁷ Temperature extremes in fusion reactors range from cryogenic in the superconducting magnets that contain the plasma to well over 1000°C for the plasma-facing first wall and diverter, which are subject to radiation by 14 MeV neutrons and thermal fluxes exceeding 20 MW/m². The neutrons interact primarily with the first wall and the breeder blanket, but affect all other components in the system,¹⁷⁸ with local temperatures influencing the extent of recovery from the radiation damage. Low-activation materials are essential to minimize radioactive waste. High-temperature superconductors for the containment magnets, Li-based oxides for the tritium breeder blanket, WC cermets for diverter shielding, SiC-based CMCs, and possibly UHTCs for plasma facing components all lack the required durability and/or functionality. The fundamental understanding of how to tailor materials for such extreme environments must be
<figure><img src="image_7.png" /><figcaption>**FIGURE 4** Challenges for ceramics in extreme environments arise across broad applications in energy, security, and transportation. Sources for images, from left to right: high-T<sub>c</sub> superconductors (HTSC) for plasma confinement<sup>147</sup> (reprinted with permission, Nature Publishing Group); armor<sup>148</sup>; ceramic-matrix composite<sup>149</sup> (reprinted with permission, General Electric Company); reaction zone between environmental barrier coating with calcium-magnesium-aluminosilicate<sup>150</sup>; and ultrahigh-temperature ceramic leading edges<sup>151</sup> (Source: NASA Ames Research Center)</figcaption></figure>

developed before implementation of fusion systems becomes a reality.

(iv) Tribological, superabrasive, and armor materials that serve under extreme static and dynamic mechanical loads, often combined with temperature extremes. These include operation at ultrahigh pressures or contact loads (10 GPa-1 TPa), such as those generated within diamond anvil cells (DACs),<sup>179</sup> machining tools (eg, cutting, drilling, grinding) which benefit from super- and ultrahard materials,<sup>180</sup> and operation under highly dynamic loads found, for example, in armor applications, where impact pressures can exceed 10 GPa.<sup>181</sup> While phase transformations under pressure can lead to the discovery of new structures with novel properties, they may also be deleterious to the expected performance, as in the solid-state amorphization of B<sub>4</sub>C under high-velocity impacts.<sup>182</sup> As is the case with ballistic armor, the discovery and fundamental understanding of superhard materials is still in its early stages of identifying and leveraging advanced simulation, synthesis, and characterization tools.

Severe environments of one sort or another are also encountered in a broad spectrum of functional applications, such as high-temperature thermoelectrics,<sup>183</sup> electrochemical systems in batteries,<sup>184</sup> solid oxide fuel cells (SOFCs),<sup>185</sup> high-voltage insulators,<sup>186</sup> magnets,<sup>187</sup> superconductors,<sup>188</sup> and optical/optoelectronic devices subject to high photon fluxes.<sup>189</sup> A common issue is the evolution of defects as the field or flux interacts with the ceramic, which limits the subsequent system performance.<sup>189</sup> Despite differences in the details of the mechanisms and associated dynamics, these issues have analogs with the categories discussed above, namely degradation by energetic particles and high-flux thermal fields, thermochemical

reactions with aggressive species, and extreme transient loads.

A fundamentally rigorous, computationally backed experimental strategy is required to elucidate the phenomena that govern extreme environment ceramics at multiple length and time scales. Most extreme environments will likely require multimaterial systems, wherein performance is not dependent solely on the properties of each individual constituent, but rather on the interplay among them.<sup>164,190</sup> From that perspective, two challenges are identified in ceramics for extreme environments, one related to discovery and design strategies for new materials and the other to improved understanding of complex systems (including interactions across interfaces) under extreme thermal, chemical, and mechanical environments. Both challenges share limitations of the theoretical and modeling infrastructure to predict behavior (even under a single extreme condition), as well as of the experimental capabilities to measure properties and assess performance in the more complex situations that combine extremes.

## 5.1 | Challenge #5: Ceramics in the extreme: Discovery and design strategies

As noted earlier, the extreme environments of interest are those for which no satisfactory materials solution yet exists, even if some materials meet a subset of the required properties. For example, UHTCs based on refractory metal borides, carbides, or nitrides exhibit some of the highest melting temperatures available and form highly refractory, stable oxides.<sup>158,163</sup> However, these oxides are porous and tend to crack due to thermal expansion mismatch with their parent material, rendering them nonprotective.<sup>191</sup> Use of
UHTC composites with SiC additions leads to a passivat-
ing liquid silicate coating that is susceptible to ablation by
turbulent flows and experiences volatilization above
~1600°C.<sup>160,163</sup> Efforts to form solid protective coatings
using rare-earth additives lead to formation of refractory
oxide scales, for example, LaZr<sub>2</sub>O<sub>7</sub>,<sup>192</sup> but these too are
unlikely to survive above ~1800°C due to thermal expan-
sion mismatch. Conversely, environmental barrier coatings
for CMCs based on rare-earth disilicates are sufficiently
refractory and better matched to the substrate than their
rare-earth monosilicate counterparts but have inferior resis-
tance to volatilization in water vapor.<sup>169</sup> Moreover, neither
ceramic has adequate resistance to attack by molten sili-
cates.<sup>173,174,193</sup> In these, as in many other cases, the known
menu of candidate materials is sparse and highlights the
critical need for the discovery/design of new materials and
architectural concepts.

Theory and computational modeling are essential tools
to guide the discovery process. The value of theory is
illustrated by recent work that provided a fundamental
explanation for the reported maximum in melting point for
rock-salt solutions of TaC–HfC at ~(Ta<sub>0.8</sub>Hf<sub>0.2</sub>)C<sub>0.875</sub>.<sup>194-197</sup>
The authors further predicted that compounds in the Hf–C–N
system could exhibit melting points at least 200°C higher
than in Ta–Hf–C, although this prediction is yet to be vali-
dated experimentally. Methods based on DFT are now able
to calculate mechanical, electronic and thermophysical prop-
erties of ceramics at low temperatures.<sup>198</sup> High-temperature
properties of ceramics require calculation of the Gibbs free
energy, which may involve electronic excitations and
defects. Such calculations are much more demanding and
not yet generally available, although an early approach for
elemental metals was demonstrated in the 1990s by DFT
calculations of the melting curve of Fe up to 6000 K in the
earth's core, at pressures up to 350 GPa.<sup>199</sup> Progress has
since enabled DFT calculations of thermal expansion and
heat capacity of pure ZrC up to 3500 K.<sup>200</sup> Although not
yet possible, extension of these ideas to the prediction of
new materials is encouraging.

Understanding phase stability and structural transforma-
tions in chemically complex systems is paramount to all dis-
covery and design strategies and arguably requires
continuum level approaches based on CALPHAD, phase
field, and other computational methods. CALPHAD has
been invaluable in providing a methodology to assess phase
equilibria in multicomponent systems, but is largely based
on fitting of free energy models to reproduce experimental
data. This presents two obstacles. First, determination of
thermodynamic properties is hindered for materials that are
not readily synthesized. Here, exploration and property pre-
dictions based on DFT may prove invaluable;²⁰¹ in fact,
ongoing activities are focusing on exploring avenues to
bypass the CALPHAD approach altogether by using DFT

and applying advanced sampling techniques.²⁰¹ The second obstacle is related to the measurement of thermodynamic properties at extreme temperatures, notably enthalpies of transformations and heat capacities.²⁰²,²⁰³ Containment of materials at these temperatures without introducing contamination or measurement artifacts is a major practical issue. This challenge can be addressed by novel calorimetric techniques combining, for example, aerodynamic levitation with laser melting.²⁰³ Examples of techniques applicable to extreme environments are illustrated in Figure 5; however, many are still emerging and much development remains. Phase transformation temperatures in the solid state can also be addressed with X-rays²⁰⁴ coupled with noncontact methods of heating, such as quadrupole lamp furnaces,²⁰⁵ though the latter are still limited to temperatures below ~ 2000°C. Resistive heating of UHTCs has been employed in oxidation studies to 2000°C,²⁰⁶,²⁰⁷ taking advantage of the metallic conductivity of refractory borides and suitable specimen design, though these approaches are limited to conductive materials and may also be prone to artifacts.²⁰⁷

While characterization of materials under combined extremes is still challenging, progress has been made in measuring behaviors in simplified environments typically dominated by a single extreme condition. For example, one can measure melting temperatures well over 3000°C using new laser techniques,²¹⁰ as demonstrated recently on HfC<sub>0.98</sub>, (3959°C±84°C).¹⁹⁵ It is also possible to measure strength,²¹¹ thermal diffusivity,²¹² heat capacity,²⁰³ coefficient of thermal expansion,²⁰⁴,²¹³ and electrical conductivity²¹⁴ at very high temperatures, as well as material responses in extreme heat fluxes.²¹⁵,²¹⁶ A limiting factor often becomes the stability and inertness of the sensors needed to measure the quantities of interest, both in the environment as well as in contact with the specimen.

Elucidating mechanical behavior at extreme temperatures still presents major barriers. Among these is the characterization of the constitutive behavior. Micromechanical models that combine the effects of composition, phase constitution, and defects, all of which can evolve over time,²¹⁷ and finite element models that can be informed by the emerging micromechanical understanding must be developed. Advances in high-resolution X-ray computed tomography provide new insights into the evolution of defects and damage with increasing strain,²¹⁸,²¹⁹ which can then illuminate the development of virtual test methods and predictive models for failure. Toughness is a particularly critical property, often limiting the applicability of ceramics, but capabilities to develop fundamental understanding of this property at extreme temperatures are lacking. Novel tests have been developed, especially for porous materials,²²⁰⁻²²² but their applicability above ambient temperature is limited by the lack of appropriate tooling and sensors, as well as the lack of models for the interpretation of results. The increasing availability of synchrotron-compatible diamond
<figure><img src="image_8.png" /></figure>

**FIGURE 5** High-temperature and high-pressure techniques applicable to extreme environmental research; clockwise from upper left: high-resolution microcomputed tomography (μ-CT) of SiC-SiC composites<sup>219</sup> (reprinted with permission, Nature Publishing Group); arc jet test<sup>151</sup> (Source: NASA Ames Research Center); diamond anvil cell for extreme pressures; ultra high-temperature (UHT) calorimetry<sup>208</sup>; and a time sequence of surface melting of silicate deposits from a high heat flux laser gradient test<sup>209</sup>

anvil cells and environmental systems with heating sources allows a wide range of high temperatures/high pressures, and controlled-environment physical properties to be monitored in situ, including structure, compressibility, elasticity, thermal expansion, transport properties, rheology, and chemical reactions.<sup>223,224</sup> However, constitutive behavior under nonhydrostatic stresses at extreme temperatures is still a challenge.

## 5.2 | Challenge #6: Ceramics in the extreme: Behavior of multimaterial systems

The complexity of extreme environments favors reliance on multiphase/multielement materials having tailored microstructures and architectures. A scientific approach that captures the complexity of the salient thermochemical and thermomechanical material interactions is essential. This includes modeling of the interactions of the constituents in different atomic scale configurations, requiring input from thermodynamic measurements to inform phase stability and kinetic models in multicomponent systems; processing approaches to develop the desired architectures; and experimental assessment of the multiphase/microstructurally designed material systems in extreme environments. In situ and operando measurements are becoming increasingly critical, requiring development of testing systems and sensors for extreme conditions.

Modeling challenges include the integration of the relevant physical phenomena within the constituents of the system, their interfaces, and the dynamics of the multimaterial assemblage to identify the performance-limiting factors in the extreme environment.<sup>225,226</sup> The overall infrastructure,

integrated along the guidelines of the materials genome initiative, requires further developments in continuum and microstructure-level models, such as those emerging from multiscale finite and discrete element methods.<sup>227</sup> Micromechanical, thermodynamic, and kinetic models are also essential. Of particular interest are models describing the oxidation of multiphase materials, especially when one or more of the oxidation products is subject to volatilization,<sup>156,161,163,228</sup> all of which are limited by insufficient thermodynamic and kinetic information. Concepts involving the development of a protective scale during extreme oxidation environments are of particular interest, especially for nonoxide ceramics.<sup>192</sup>

Extensive experimental infrastructure, both user facilities as well as laboratory-scale academic capability, is needed to meet this grand challenge for both scientific and technological progress as well as training a generation of new researchers. Examples of critical facilities include plasma and wind tunnels for testing under hypersonic conditions,<sup>154,157,162,229,230</sup> facilities for studying nuclear radiation effects on fusion materials, and also for the study of materials under high heat fluxes.<sup>231,232</sup>

While some facilities capable of simulating complex in-service environments are in place (eg, for simulation of environments relevant to turbine engines<sup>217,232,233</sup>), their capabilities are still limited, for example, to quantitatively assess the effects of ionic dissociation in hypersonics, or the role of water vapor at high pressures and high velocities. In situ measurements of material characteristics and operando monitoring of materials evolution are critically needed to enable a quantitative understanding of the
composition-structure-property relations in a complex environment. Using X-rays as probes, especially in combination with µ-CT, one should be able to assess the synergistic effects of temperature, environment, and stress on the mechanical properties and the mechanisms of failure,²¹⁹,²²⁰,²³⁴ phase stability, oxidation, oxidation-induced stresses,²³⁵ and effects of high-temperature corrosion by CMAS²³⁶,²³⁷ and gradients in internal strain.²³⁸

## 6 | GLASSES

The current status and future outlook of glass science and engineering were recently discussed in two splendid reviews.²³⁹,²⁴⁰ The challenges in glass science and engineering identified here build on these and other recent advances and emerging opportunities.

### 6.1 | Challenge #7: Understanding and exploiting glasses and melts under extreme conditions

By studying the responses of glasses and melts to extremes in temperature, pressure, deep super-cooling, or steep chemical, electrochemical, and magnetic gradients using in situ or operando characterization tools and methods, knowledge of the glassy state can be substantially extended. Analogous to challenges posed for crystalline ceramics in Challenge #5, some extreme conditions can be used to synthesize novel glasses with new and unexpected properties and functionalities that are otherwise not possible with conventional processing techniques. Furthermore, designing new and novel glasses that function under such extreme conditions is likewise important for a variety of applications, including electrochemical, aerospace, and biomedical.

Among the extremes, pressure and temperature are important basic thermodynamic variables that determine the structure, dynamics, and macroscopic properties of glasses and glass-forming liquids.²⁴¹ Artisans, technologists, and scientists tailor glass properties (and structures) by controlling thermal history. Because of experimental difficulties, the pressure variable has been used sparingly to modify glass properties, even though available literature shows that pressure could be very effective in synthesizing novel glasses with desirable properties²⁴² and could provide a better understanding of the glass transition²⁴³,²⁴⁴ as well as phenomena like polyamorphism.²⁴⁵⁻²⁵⁰ The pressure variable can be employed to help advance glass science and technology in at least two different ways: (i) to gain insights into glass structure and properties by, for example, characterizing how pressure affects the mechanical response of glass (crack resistance, elasticity/plasticity, and

equation of state, etc.); and (ii) using pressure as a synthesis parameter to tailor the structure and properties of glass beyond what can be achieved just through composition and/or thermal control alone.

Most of the high-pressure studies on glasses have been done by the geoscience community on geologically relevant systems using multianvil apparatuses (MAA) or diamond anvil cells (DAC) to provide a better understanding of volcanology and/or magmatic processes. High-pressure apparatuses with and without resistive or laser heating have been integrated with synchrotron X-ray and neutron diffraction, inelastic X-ray scattering, Raman and Brillouin light scattering, X-ray absorption spectroscopy (XAS) (including both X-ray absorption near-edge structure [XANES] and extended X-ray absorption fine structure [EXAFS]) to study the physical and chemical properties of glasses and melts under high-pressure/high-temperature conditions.²⁵¹⁻²⁵⁵ Fairly recently, in situ high-pressure nuclear magnetic resonance (NMR) probes that can operate at pressures up to 2.5 GPa have been developed to study the structure of glass under pressure.²⁵⁶ In situ high-pressure/temperature studies have been done on prototypical network-forming oxide glasses, such as SiO₂, GeO₂, B₂O₃, etc.²⁴⁵⁻²⁵⁰; however, much less is known about the structure and properties of multicomponent glasses and melts under pressure. A close collaboration between researchers in the glass science and geoscience communities is needed to adapt these in situ high-pressure/temperature characterization techniques to study multicomponent glasses²⁵⁷⁻²⁵⁹ and melts, particularly those which are of industrial relevance and technological importance, for example, new kinds of solid electrolytes for safer and higher energy density batteries.

Pressure effects on structure and properties are generally studied on quenched glasses after application of pressure. Pressurization is either carried out at room temperature or at elevated temperatures, near the glass-transition temperature ($T_g$).²⁶⁰ Studies have shown that pressure quenching is an effective way to change the atomic packing and bonding of glasses.²⁶¹ Pressure quenching can be used to prepare glasses with different structures and properties, and this approach is easier than the hyperquenching technique,²⁶²⁻²⁶⁴ especially for the synthesis of bulk samples. For example, while pristine silica glass deforms predominantly via densification under indentation, densified silica glass is capable of shear flow under indentation,²⁶⁵ which was confirmed in classical molecular dynamics (MD) simulations²⁶⁶ (Figure 6). Pressure-quenched glasses with high elastic moduli and high thermomechanical stability may find potential applications in many fields of technological importance such as the aerospace industries.²⁶⁵ Recent studies have shown that the same degree of densification induced by cold compression at room temperature or hot compression near $T_g$, or by annealing at ambient pressure can lead
<figure><img src="image_9.png" /><figcaption>**FIGURE 6** Atomic configuration (first row), local shear strain (second row), local density (third row), and local density change mapping (fourth row) under indenter after nanoindentation test for silica glass quenched under 0 GPa and 15 GPa²⁶⁶</figcaption></figure>

to different structure and properties.²⁶⁰,²⁶⁷ These findings indicate new possibilities for the rational design of glasses with fine-tuned properties otherwise not possible through conventional composition and/or thermal control. Furthermore, hot compression of glass in the nonrigid state in the glass transition range may also provide a means to study the structure and properties of glass-forming liquids under pressure, which is of critical importance to understand geological processes in the Earth's interior.

Among high-temperature and high-pressure apparatuses, DAC can achieve very high pressures (>100 GPa) and very high temperatures (>3000 K with laser heating), but the sample size is very small, typically on the order of tens of µm.³ Similar pressures and temperatures have been achieved by MAA techniques, but with significantly larger (mm³) samples.²⁶⁸ Larger samples (cm³) cooled from high temperatures and modest pressures (up to 1 GPa) are possible using a recently opened gas-medium high-temperature and high-pressure facility in Poland,²⁶⁹ making it now possible to study the effects of pressure on macroscopic properties and to use conventional structural characterization techniques. Further development of large volume high-temperature and high-pressure techniques is needed to enable in-depth studies of glasses and melts under pressure.

Another way of exploring the properties of melts under unusual conditions, particularly those that do not readily form glasses on quenching, is to subject them to deep undercooling in ways that minimize heterogeneous nucleation initiated at container walls, or that avoid homogeneous nucleation by rapid undercooling. For instance, splat quenching techniques, with cooling rates reaching 10⁶-10⁷°C/s, were employed to synthesize amorphous metallic alloys.²⁷⁰ That original work has led to extensive investigation of “metallic glasses” as they later became known, ultimately succeeding in establishing composition-driven predictive capabilities for bulk glass formation, glass stability, and nanocrystallization in such systems.²⁷¹ In many

respects, the original research in systems requiring extraordinarily high cooling rates built a foundation for the synthesis of novel bulk metallic glasses that can now be prepared under more normal processing conditions, with some of the best glass-forming alloys now being prepared at cooling rates as low as 0.5°C/min.²⁷² Rapid quenching techniques have been used by many in the inorganic glass community, most actively in the 1970s and 1980s,²⁷³⁻²⁷⁵ although most of these studies were done to catalog unusual glass-forming systems. In some cases, unusual properties were measured for these rapidly quenched systems, including high ionic conductivity²⁷⁶ and magnetic properties.²⁷⁴ Additional examples of glass formation in technologically important Al₂O₃-based systems have been reported more recently.²⁷⁷,²⁷⁸ Yet, overall this research has not yielded predictive capabilities beyond fairly trivial “eutectic” and “mixed metal-oxide, kitchen sink” rules, let alone formation of novel glasses utilizing conventional glass synthesis approaches.

Containerless melting techniques, such as laser melting combined with levitation, are uniquely suited for studies of deeply supercooled melts. These techniques emerged relatively recently and have been used for studies of interesting phenomena such as polyamorphic glass transitions in Al₂O₃-Y₂O₃ system.²⁷⁷ They also provide a viable way to form novel glasses with unique properties otherwise not possible with conventional glass-forming techniques, such as TiO₂-, Ta₂O₅-, WO₃-, and Al₂O₃-based glasses without any classical network formers.²⁷⁹⁻²⁸⁴ It was recently shown that Al₂O₃-SiO₂ binary glasses with up to 60 mol% Al₂O₃ could be synthesized by using the containerless technique and that these glasses possess high elastic moduli, high hardness, and high crack resistance²⁸⁵ (see Figure 7).

Combining containerless melting with in situ characterization capabilities is a powerful tool to study the structure and dynamics of deeply supercooled liquids without contamination or crystallization. First principles theoretical
<figure><img src="image_10.png" /><figcaption>**FIGURE 7** Composition dependence of elastic moduli (left) and Vickers hardness (right) for the xAl₂O₃-(100-x)SiO₂ glasses. Vickers indentation imprints for the xAl₂O₃-(100-x)SiO₂ glasses. Blue-shaded photographs show the cracked samples. Gray-shaded photographs show the noncracked samples²⁸⁵</figcaption></figure>

calculations of structures present in deeply supercooled melts should further shed light on such important aspects as network connectivity and viscosity-temperature profiles. A combination of experimental and theoretical studies should further advance the understanding of whether the designation “glass” can be used for such “frozen melts.” A solid that is X-ray amorphous could be designated as a noncrystalline solid (NCS) or a short-range order solid (SROS), but without evidence of a glass transition, a more restrictive “glass” designation is unwarranted.

Levitation systems have been combined with synchrotron X-ray and neutron diffraction at Argonne and Oak Ridge National Laboratories to study glasses and supercooled liquids,²⁸⁶,²⁸⁷ although few such systems are available at universities. Combing levitation systems with high-speed cameras and various diffraction and scattering techniques will enable us to study a range of structural, thermodynamic, viscoelastic properties of glasses and melts.

## 6.2 | Challenge #8: Rational design of functional glasses guided by predictive modeling

The traditional approach for glass research is largely empirical. A rational design approach to develop new glasses with desired properties and functionalities is usually hampered by the lack of understanding of the impact of composition and processing conditions (eg, thermal or pressure history) on the resulting glass structures and macroscopic properties. Although multiscale computer simulation and modeling techniques have been widely applied to study the structure and properties of glass²⁸⁸ (see Figure 8), they have only achieved limited success to date. This is due in part to the limited time (~µs) and length (~µm) scales accessible by even the most powerful parallel computers and to the deficiencies in existing techniques, such as the lack of reliable structural models for first principles calculations and potential models for classical MD simulations. More importantly, to design multifunctional

glasses, models at different scales are needed to predict manufacturing-related attributes, for example, temperature-dependent viscosity, liquidus temperatures, and refractory compatibility, as well as the relevant end-use properties, for example, elastic moduli, hardness, and damage resistance for cover glass in personal electronics. It remains a challenge to have all models validated by experiments, often information from a smaller scale model is used to fit and validate models at larger scales. For example, force fields used in classical MD simulations are often developed by using first principles data to fit the potential parameters, while outputs from MD simulations, such as atomic structure, elastic moduli, and diffusion coefficients are used as inputs in topological constraint modeling, finite element analysis, and analytical modeling. Thus, it is of critical importance to ensure that the fundamental chemistry and physics of glass are built into the models used in first principles calculations and in classical MD and Monte Carlo simulations.

Predictive modeling of the mechanical, electronic, electrochemical, thermal, and optical properties of glass and amorphous solids using first-principle techniques (eg, DFT) mandates the construction of structural models that properly reflect experimentally relevant glassy states. Such structural models are relatively well established for simple glasses such as vitreous silica,²⁸⁹⁻²⁹¹ but more often than not are inaccessible for complex multicomponent glass systems. The challenge of building realistic structural models for laboratory glass is twofold. From the modeling side, all structural models must be completely relaxed to a desired level of accuracy for first principles simulations such that they can be used in electronic structure calculation and for subsequent quantum mechanical modeling of physical properties. For complex glass systems, in particular nonoxide glasses where reliable interatomic potentials are often not available, ab initio molecular dynamics (AIMD) in principle offers a viable alternative to classical MD. However, due to its excessive computational needs, AIMD is severely limited in size and time scales and therefore
<figure><img src="image_11.png" /><figcaption>**FIGURE 8** Overview of modeling techniques for glasses, from purely empirical models to those firmly grounded in fundamental physics<sup>288</sup> (reprinted with permission, American Chemical Society)</figcaption></figure>

cannot represent realistic glass-forming processes. Building structural models for solids under external stimuli (eg, photosensitive glass under light exposure) presents an additional challenge. On the experimental end, quantitative glass structure characterization typically relies on diffraction techniques or advanced imaging tools. For multicomponent glasses consisting of atoms of similar sizes, accurate structure identification remains a challenging task. Furthermore, structure factors and pair distribution functions obtained from diffraction measurements are one-dimensional functions that are inherently unable to fully capture the three-dimensional glass structure. Classical reverse Monte Carlo (RMC) simulations<sup>292</sup> as well as emerging, further refined computational methods<sup>293</sup> allow inversion of diffraction data to extract glass structures, although still with some ambiguity. Advanced atomic scale imaging based on electron microscopy complements diffraction techniques by providing direct visualization of glass structures in real space. For instance, electron tomography is now applied to the reconstruction of three-dimensional amorphous structures with nanometer spatial resolution.<sup>294</sup> The direct imaging of two-dimensional silica glass comprising bilayers of SiO<sub>4</sub> tetrahedra using STEM is another salient example.<sup>295</sup> Nevertheless, the imaging approach requires complicated sample preparation and also poses constraints on sample dimensions, and are only suited for model validation rather than predictive material design. Overall, construction of realistic glass structural models for first principles predictive modeling of mechanical, electronic, electrochemical, and optical properties in glasses remains a standing challenge. Resolving this

challenge will entail the development of new efficient modeling techniques as well as reliable, large-scale structure characterization methods. It is worth mentioning that high-throughput synthesis and measurement methods, coupled with data-based materials informatics, will likely complement first principles approaches to enable predictive modeling capabilities for glass materials.

Because of the semiempirical nature of interaction potential models used in atomistic simulations, they must be validated against experimental or first principles data. This is done by optimizing potential parameters to reproduce the physical properties of known structures, for example, static properties, such as bonding energy, density, bond lengths, bond angles, structure factors, and elastic moduli, and dynamic properties, such as the vibrational density of states (VDOS), IR, and Raman spectra, as well as transport properties, such as diffusion coefficients. The position and depth of the potential well largely determines bond length, density, and defect formation energy, while the shape of the minimum affects atomic vibrations and elastic moduli. It is the shape of the tail that mainly tells how easily atoms can migrate out of the potential well. Most of the force fields were developed by mainly using structural information and properties near the potential minimum (dominated by the harmonic part) from experiments or first principles calculations at ambient conditions. High-temperature in situ characterization of well-designed model systems is needed to provide structure and properties determined by the anharmonic part of the potential to fit and validate computer models, such as thermal expansion coefficient or viscosity/diffusion coefficient. Levitation
combined with laser heating and in situ characterizations
can be a viable and “clean” way to obtain such structure
and properties of glasses at high temperatures, especially
for compositions that may not be stable using conventional
routes. Studies of the structure and properties of glass
under high pressure, similar to those suggested for poly-
crystalline ceramics in Challenge #5, can provide inputs for
fitting or validating the repulsive part of the interaction
potential. Reasonably accurate potential models are avail-
able for simple silicate glasses, but for borate glasses, phos-
phate glasses, or multicomponent glasses with mixed
network formers, such force fields are currently lacking.
Therefore, there is a pressing need to develop potential
models for such systems to enable predictive design of
their structure and properties.

Human-produced glasses have been available for 5000+
years, but many puzzles related to their structural and
dynamic nature remain, in situ or operando characterization,
and modeling of glasses and melts are needed to develop pre-
dictive computer models. With reliable and predictive com-
puter models, glass compositions and/or processing
conditions for various applications starting from atomic
structure models from simulations can be designed. This can
dramatically change the nature of glass research and, just like
designing new drugs in the pharmaceutical industry, will
allow for the design of new functional glasses based on com-
putations, including those with high strength, high fracture
toughness, or high ionic conductivity.

7 | SUMMARY

Eight grand challenges for fundamental ceramic and glass science research form the basis for progress in creating knowledge with transformational technological impact potential. These challenges focus on strategies for the design of new materials and understanding of their structure and properties. Ultimately, these are expected to afford new capabilities in function and performance. The challenges demand innovation in both experiments and models; in the former, for example, at extreme conditions of temperature, pressure, or radiation flux, while in the latter, for instance, models for defect-defect interaction, particularly for cases with large defect concentrations, and defects confined in 2D arrays, are particularly vexing. It is anticipated that these challenges will provide inspiration for research in the ceramic and glass communities with societal and industrial import.

ACKNOWLEDGMENTS

This workshop and the resulting report were supported by
NSF DMR-1619666. The assistance of Thorston Bayer

(The Pennsylvania State University), Joseph Muth (Harvard
University), and Xiaoting Zhong (Carnegie Mellon Univer-
sity) as scribes during the workshop is greatly appreciated.
Joshua C. Agar (University of California, Berkeley) assem-
bled Figure 3. The co-organizers thank Dr. Lynnette Mad-
sen for her counsel during the planning and conduct of the
workshop.

REFERENCES

1. Deville S, Stevenson AJ. Mapping ceramics research and its evolution. *J Am Ceram Soc*. 2015;98:2324-2332.

2. http://www-unix.ecs.umass.edu/~jakus/nsf/nsf.ceramics.report6.pdf. Accessed September 12, 2016

3. Rohrer GS, Affatigato M, Backhaus M, et al. Challenges in ceramic science: a report from the workshop on emerging research areas in ceramic science. *J Am Ceram Soc*. 2012;95:3699-3712.

4. Innovation in Industry. Catch the wave: the long cycles of industrial innovation are becoming shorter. *Economist*. February 18, 1999 www.economist.com/node/186628, Accessed January 9, 2015.

5. Hargroves K, Smith MH. The Natural Advantage of Nations: Business Opportunities, Innovation and Governance in the 21st Century. London: Earthscan; 2005.

6. Pollock TM, Allison JE, Backman DG, et al. Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security. Washington, DC: National Academy of Sciences; 2008.

7. Rondinelli JM, Poeppelmeier KR, Zunger A. Research update: towards designed functionalities in oxide-based electronic materials. *APL Mater*. 2015;3:080702.

8. Wang Y, Richards WD, Ong SP, et al. Design principles for solid-state lithium superionic conductors. *Nat Mater*. 2015;14: 1026.

9. Li B, Osada M, Ozawa TC, et al. Engineered interfaces of artificial perovskite oxide superlattices via nanosheet deposition process. *ACS Nano*. 2010;4:6673-6680.

10. Li B, Osada M, Ebina Y, Ueda S, Sasaki T. Coexistence of magnetic order and ferroelectricity at 2D nanosheet interfaces. *J Am Chem Soc*. 2016;138:7621-7625.

11. Wang Y, Wang Y, Breed DR, et al. Colloids with valence and specific directional bonding. *Nature*. 2012;491:51-55.

12. Auyeung E, Li T, Senesi AJ, et al. DNA-mediated nanoparticle crystallization into Wulff polyhedral. *Nature*. 2014;505:73.

13. Chaudhary K, Chen Q, Juarez JJ, Granick S, Lewis JA. Janus colloidal matchsticks. *J Am Chem Soc*. 2012;134:12901-12903.

14. Plunkett K, Mohraz A, Lewis JA, Moore JS. Light-regulated electrostatic interactions in colloidal suspensions. *J Am Chem Soc*. 2005;127:14574-14575.

15. Chaudhary K, Juarez J, Chen Q, Granick S, Lewis JA. Reconfigurable assemblies of Janus rods in AC electric fields. *Soft Matter*. 2014;10:1320-1324.

16. Gangwal S, Cayre OJ, Velev OD. Dielectrophoretic assembly of metallodielectric Janus particles in AC fields. *Langmuir*. 2008;24:13312-13320.

17. Poterala SF, Meyer RJ, Messing GL. Low-field dynamic magnetic alignment and templated grain growth of diamagnetic PMN-PT ceramics. *J Mater Res*. 2013;28:2960-2969.
18. Sakka Y, Suzuki TS, Uchikoshi T. Fabrication and some properties of textured alumina-related compounds by colloidal processing in high-magnetic field and sintering. *J Eur Ceram Soc.* 2008;28:935-942.

19. Cesarano J III, Calvert P. Freeforming Objects with Low-Binder Slurry. U.S. Patent 6,027,326, 2000.

20. Cesarano J III, Segalman R, Calvert P. Robocasting provides moldless fabrication from slurry deposition. *Ceram Ind.* 1998;148:94.

21. Smay JE, Cesarano J, Lewis JA. Colloidal inks for directed assembly of 3-D periodic structures. *Langmuir.* 2002;18:5429-5437.

22. Eckel ZC, Zhou C, Martin JH, Jacobsen AJ, Carter WB, Schaebler TA. Additive manufacturing of polymer-derived ceramics. *Science.* 2016;351:58-62.

23. Halloran JW. Ceramic stereolithography: additive manufacturing for ceramics by photopolymerization. *Annu Rev Mater Res.* 2016;46:19-40.

24. Maloney KJ, Roper CS, Jacobsen AJ, Carter WB, Valdevit L, Schaebler TA. Microlattices as architected thin films: analysis of mechanical properties and high strain elastic recovery. *APL Mater.* 2013;1:022106.

25. Meza LR, Das S, Greer JR. Strong, lightweight, and recoverable three-dimensional ceramic nanolattices. *Science.* 2014;345:1322-1326.

26. Zanchetta E, Cattaldo M, Franchin G, et al. Stereolithography of SiOC ceramic microcomponents. *Adv Mater.* 2016;28:370-376.

27. Zheng X, Lee H, Weisgraber TH, et al. Ultralight, ultrastiff mechanical metamaterials. *Science.* 2014;344:1373.

28. Sun K, Wei T-S, Ahn BY, Seo JY, Dillon SJ, Lewis JA. 3D printing of interdigitated Li-ion microbattery architectures. *Adv Mater.* 2013;25:4539.

29. Mohraz A, Weeks ER, Lewis JA. Structure and dynamics of biphasic colloidal mixtures. *Phys Rev E.* 2008;77:060403.

30. Ober TJ, Foresti D, Lewis JA. Active mixing of complex fluids at the microscale. *Proc Natl Acad Sci.* 2015;12:12293-12298.

31. Hardin JO, Ober TJ, Valentine AD, Lewis JA. Microfluidic printheads for multi-material 3D printing of viscoelastic inks. *Adv Mater.* 2015;27:3279-3284.

32. Bauer J, Hengsbach S, Tesari I, Schwaiger R, Kraft O. High-strength cellular ceramic composites with 3D microarchitecture. *Proc Natl Acad Sci.* 2014;111:2453-2458.

33. Zocca A, Colombo P, Gomes CM, Günster J. Additive manufacturing of ceramics: issues, potentialities, and opportunities. *J Am Ceram Soc.* 2015;98:1983-2001.

34. Kähäri H, Teirikangas M, Juuti J, Jantunen H. Dielectric properties of lithium molybdate ceramic fabricated at room temperature. *J Am Ceram Soc.* 2014;97:3378-3379.

35. Guo J, Guo H, Baker A, et al. Cold sintering: a paradigm shift for processing and integration of ceramics. *Angew Chem Int Ed.* 2016;55:11457-11461.

36. Guo J, Berbano SS, Guo H, Baker AL, Lanagan MT, Randall CA. Cold sintering process of composites: bridging the processing gap of ceramics and polymers. *Adv Funct Mater.* 2016;26:7115-7121.

37. Colombo P. In praise of pores. *Science.* 2008;322:381-383.

38. Burke K. Perspective on density functional theory. *J Chem Phys.* 2012;136:1590901.

39. Calderon CE, Plata JJ, Toher C, et al. The AFLOW standard for high-throughput materials science calculations. *Comput Mater Sci.* 2015;108[Part A]:233-238.

40. van Duin ACT, Dasgupta S, Lorant F, Goddard WA III. ReaxFF: a reactive force field for hydrocarbons. *J Phys Chem A.* 2001;105:9396-9409.

41. Focus Section on Semi-Empirical Interatomic Potentials. In: Muser MH, eds. *Modelling and Simulation in Materials Science and Engineering*. Philadelphia, PA: IOP; 2015:23.

42. Trott CR, Hammond SD, Thompson AP. SNAP: strong scaling high fidelity molecular dynamics simulations on leadership-class computing platforms. *Int Supercomputing Conf.* 2014;19-34.

43. Brommer P, Kiselev A, Schopf D, Beck P, Roth J, Trebin H-R. Classical interaction potentials for diverse materials from *ab initio* data: a review of potfit. *Modell Simul Mater Sci Eng.* 2015;23:074002.

44. Thompson P, Swiler LP, Trott CR, Foiles SM, Tucker GJ. Spectral neighbor analysis method for automated generation of quantum-accurate interatomic potentials. *J Comput Phys.* 2015;285:316.

45. Steinbach I. Phase-field model for microstructure evolution at the mesoscopic scale. *Annu Rev Mater Res.* 2013;43:89-107.

46. Holm EA, Battaile CC. The computer simulation of microstructural evolution. *J Met.* 2001;53:20-23.

47. Dimiduk DM. Microstructure-Property-Design Relationships in the Simulation Era: An Introduction. In: Dimiduk D, Ghosh S, eds. *Computational Methods for Microstructure-Property Relationships*. US: Springer; 2010.

48. The Minerals, Metals & Materials Society (TMS). Modeling Across Scales: A Roadmapping Study for Connecting Materials Models and Simulations Across Length and Time Scales. Warrendale, PA: TMS; 2015.

49. Schmalzried H. *Chemical Kinetics of Solids*. Weinheim: VCH; 1995.

50. Maier J. *Physical Chemistry of Ionic Materials: Ions and Electrons in Solids*. Weinheim: Wiley Verlag; 2004.

51. Mebane DS, De Souza RA. A generalized space-charge theory for extended defects in oxygen-ion conducting electrolytes: from dilute to concentrated solid solutions. *Energy Environ Sci.* 2015;8:2935-2940.

52. Mo K, Zhau Z, Miao Y, et al. Synchrotron study on load partitioning between ferrite/martensite and nanoparticles of a 9Cr ODS steel. *J Nucl Mater.* 2014;445:209-217.

53. Sun L, Marrocchelli D, Yildiz B. Edge dislocation slows down oxide ion diffusion in doped CeO₂ by segregation of charged defects. *Nat Commun.* 2015;6:6294.

54. Maier J. Crystalline solid electrolytes and defect chemistry: some novel thermodynamic and kinetic results. *Solid State Ionics.* 1996;86-88:55-57.

55. Alonso JL. Phase diagram and influence of defects in the double perovskites. *Phys Rev B.* 2003;76:214423.

56. Korobko R, Patlolla A, Kossoy A, et al. Giant electrostriction in Gd-doped ceria. *Adv Mater.* 2012;24:5857-5861.

57. De Souza RA. Introduction to the special issue on defects and transport in complex oxides. *Comput Mater Sci.* 2015;103:205.

58. Pramanick D, Damjanovic D, Daniels JE, Nino JC, Jones JL. Origins of electro-mechanical coupling in polycrystalline ferroelectrics during subcoercive electrical loading. *J Am Ceram Soc.* 2011;94:293-309.

59. Marincel DM, Zhang K, Jesse S, et al. Influence of a single grain boundary on domain wall motion in ferroelectrics. *Adv Funct Mater.* 2014;24:1409-1417.
60. Bintachitt P, Jesse S, Damjanovic D, et al. Collective dynamics underpins Rayleigh behavior in disordered polycrystalline ferroelectrics. *Proc Natl Acad Sci.* 2010;107:7219-7224.

61. Dedon LR, Saremi S, Chen ZH, et al. Nonstoichiometry, structure, and properties of BiFeO₃ films. *Chem Mater.* 2016;28:5952-5961.

62. Rost CM, Sachet E, Borman T, et al. Entropy-stabilized oxides. *Nat Commun.* 2015;6:8485.

63. Koumoto K, Funahashi R, Guilmeau E, et al. Thermoelelctric ceramics for energy harvesting. *J Am Ceram Soc.* 2012;96:1-23.

64. Backhaus-Ricoult M, Rustad J, Moore L, Smith C, Brown J. Semiconducting large bandgap oxides as potential thermoelectric materials for high-temperature power generation? *Appl Phys A.* 2014;116:433-470.

65. Biskup N, Salafranca J, Mehta V, et al. Insulating ferromagnetic LaCoO₃-δ films: a phase induced by ordering of oxygen vacancies. *Phys Rev Lett.* 2014;112:087202-087205.

66. Yang JJ, Strukov DB, Stewart DR. Memristive devices for computing. *Nat Nanotechnol.* 2013;8:13-24.

67. Messerschmitt F, Kubicek M, Schweiger S, Rupp JL. Memristor kinetics and diffusion characteristics for mixed anionic-electronic SrTiO₃-δ bits: the memristor-based cottrell analysis connecting material to device performance. *Adv Funct Mater.* 2014;24:7448-7460.

68. Breckenfeld E, Bronn N, Karthik J, et al. Effect of growth induced (non) stoichiometry on interfacial conductance in LaAlO₃/SrTiO₃. *Phys Rev Lett.* 2013;110:196804.

69. Warusawithana MP, Richter C, Mundy JA, et al. LaAlO₃ stoichiometry is key to electron liquid formation at LaAlO₃/SrTiO₃ interfaces. *Nat Commun.* 2013;4:2351.

70. Sato HK, Bell C, Hikita Y, Hwang HY. Stoichiometry control of the electronic properties of the LaAlO₃/SrTiO₃ heterointerface. *Appl Phys Lett.* 2013;102:251602.

71. Breckenfeld E, Bronn N, Mason N, Martin LW. Tunability of conduction at the LaAlO₃/SrTiO₃ heterointerface: thickness and compositional studies. *Appl Phys Lett.* 2014;105:121610.

72. Kalinin SV, Borisevich A, Fong D. Beyond condensed matter physics on the nanoscale: the tole of ionic and electrochemical phenomena in the physical functionallities of oxide materials. *ACS Nano.* 2012;6:10423-10437.

73. Breckenfeld E, Shah AB, Martin LW. Strain evolution in non-stoichiometric heteroepitaxial thin-film perovskites. *J Mater Chem C.* 2013;1:8052-8059.

74. Minato T, Kawai M, Kim Y. Creation of single oxygen vacancy on titanium dioxide surface. *J Mater Res.* 2012;27:2237-2240.

75. Adepalli KK, Kelsch M, Merkle R, Maier J. Influence of line defects on the electrical properties of single crystal TiO₂. *Adv Funct Mater.* 2013;23:1798-1806.

76. Morozovska AN, Eliseev EA, Tagantsev AK, Bravina SL, Chen L-Q, Kalinin SV. Thermodynamics of electromechanically coupled mixed ionic-electronic conductors: deformation potential, Vegard strains, and flexoelectric effect. *Phys Rev B.* 2011;83:195313.

77. Damodaran AR, Breckenfeld E, Chen Z, Lee S, Martin LW. Enhancement of ferroelectric Curie temperature in BaTiO₃ films via strain-induced defect dipole alignment. *Adv Mater.* 2014;26:6341-6347.

78. Wang Z, Loon A, Subramanian A, et al. Transition from reconstruction toward thin film on the (110) surface of strontium titanate. *Nano Lett.* 2016;16:2407-2412.

79. Lee W, Han JW, Chen Y, Cai Z, Yildiz B. Cation size mismatch and charge interactions drive dopant segregation at the surfaces of manganite perovskites. *J Am Chem Soc.* 2013;135:7909-7925.

80. Backhaus-Ricoult M. Interface chemistry in LSM-YSZ composite SOFC cathodes. *Solid State Ionics.* 2006;177:2195-2200.

81. Tsvetkov N, Lu Q, Sun L, Crumlin E, Yildiz B. Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface. *Nat Mater.* 2016;15:1010-1016.

82. Jacobs R, Booske J, Morgan D. Understanding and controlling the work function of perovskite oxides using density functional theory. *Adv Funct Mater.* 2016;10:1002.

83. Fan Y, Osetskly YN, Yip S, Yildiz B. Mapping strain rate dependence of dislocation-defect interactions by atomistic simulations. *Proc Natl Acad Sci.* 2013;110:17756-17761.

84. Carter EA. Challenges in modeling materials properties without experimental input. *Science.* 2008;321:800.

85. Knauth P. Inorganic solid Li ion conductors: an overview. *Solid State Ionics.* 2009;180:911-916.

86. Saremi S, Xu R, Dedon LR, et al. Enhanced electrical resistivity and properties via ion bombardment of ferroelectric thin films. *Adv Mater.* 2016;10:1002.

87. Sata N, Eberman K, Eberl K, Maier J. Mesoscopic fast ion conduction in nanometre-scale planar heterostructures. *Nature.* 2000;408:946-949.

88. Sang X, LeBeau JM. Revolving scanning transmission electron microscopy: correcting sample drift distortions without prior knowledge. *Ultramicroscopy.* 2014;138:28-35.

89. Yankovich AB, Berkels B, Dahmen W, et al. Picometre-precision analysis of scanning transmission electron microscopy images of platinum catalysis. *Nat Commun.* 2014;5:4155.

90. LeBeau JM, Findlay SD, Allen LJ, Stemmer S. Standardless atom counting in scanning transmission electron microscopy. *Nano Lett.* 2010;10:4405-4408.

91. Muller DA, Kourkoutis LF, Murfitt M, et al. Atomic-scale chemical imaging of composition and bonding by aberration-corrected micrscopy. *Science.* 2008;319:1073-1076.

92. Varela M, Findlay SD, Lupini AR, et al. Spectroscopic imaging of single atoms within a bulk solid. *Phys Rev Lett.* 2004;92:95502.

93. Allard LF, Bigelow WC, Jose-Yacaman M, Nackashi DP, Damiano J, Mick SE. A new MEMS-based system for ultra-high-resolution imaging at elevated temperatures. *Microsc Res Tech.* 2009;72:208-215.

94. Baier S, Wittstock A, Damsgaard CD, et al. Influence of gas atomospheres and ceria on the stability of nanoporous gold studied by environmental electron microscopy and in situ ptychography. *RSC Adv.* 2016;6:83031-83043.

95. Backhaus-Ricoult M, Adib K, Clair TS, Luerssen B, Gregoratti L, Barinov A. In-situ study of operating SOFC LSM/YSZ cathodes under polarization by photoelectron microscopy. *Solid State Ionics.* 2008;179:891-895.

96. Backhaus-Ricoult M, Work K, Adib K, Gregoratti L, Amati M. Impact of surface chemistry on the electrochemical performance of perovskite cathodes. *ECS Trans.* 2014;61:3-21.

97. Backhaus-Ricoult M, Adib K, Work K, et al. In-situ scanning photoelectron microscopy study of operating (La, Sr)FeO₃-based NOₓ-sensing surfaces. *Solid State Ionics.* 2012;225:716-726.
98. Castell MR. Scanning tunneling microscopy of reconstructions of the SrTiO₃(001) surface. *Surf Sci.* 2002;505:1-13.

99. Zhou MJ, Yan L, Fu EG, et al. Phase transformations and defect clusters in single crystal SrTiO₂ irradiated at different temperatures. *J Nucl Mater.* 2013;442:143-147.

100. Lee C-H, Orloff ND, Birol T, et al. Exploiting dimensionality and defect mitigation to create tunable microwave dielectrics. *Nature.* 2013;502:532-536.

101. Zhou YC, Hashida T. Delamination cracking in thermal barrier coating system. *J Eng Gas Turbines Power.* 2002;124:922-930.

102. Lee S, Seo H, Lucovsky G, Fleming LB, Ulrich MD, Lüning J. Bulk defects in nano-crystalline and in non-crystalline HfO₂-based thin film dielectrics. *Thin Solid Films.* 2008;517:437-440.

103. Fuelcells. https://fuelcellsworks.com/archives/2012/03/30/world-record-julich-fuel-cell-passes-40000-hour-mark/, Accessed December 8, 2016.

104. Memristor. https://en.wikipedia.org/w/index.php?title=Special:CiteThisPage&page=Memristor&id=766832362. Accessed December 8, 2016.

105. Cellular technology. https://madeby.google.com/phone/, Accessed December 8, 2016.

106. Turbine blades. http://www.supergenple.net/themes/theme2/turbines.png. Accessed December 8, 2016.

107. Electron gun. http://www.rbdinstruments.com/blog/tag/filament/, Accessed December 8, 2016.

108. Coleman JN, Lotya M, O'Neill A, et al. Two-dimensional nanosheets produced by liquid exfoliation of layered materials. *Science.* 2011;331:568-571.

109. Qian H, Luo J. Vanadia-based equilibrium-thickness amorphous films on anatase (101) surfaces. *Appl Phys Lett.* 2007;91:061909 doi:10.1063/1.2768315.

110. Dillon SJ, Tang M, Carter WC, Harmer MP. Complexion: a new concept for kinetic engineering in materials science. *Acta Mater.* 2007;55:6208-6218

111. Treacy MMJ, Rice SB, Jacobson AJ, Lewandowski JT. Electron-microscopy study of delimitation in dispersions of the perovskite-related layered phases of KCa₂Na₃NbₙO₃n+1 - evidence for single-layer formation. *Chem Mater.* 1990;2:279-286.

112. Nicolosi V, Chhowalla M, Kanatzidis MG, Strano MS, Coleman JN. Liquid exfoliation of layered materials. *Science.* 2013;340: 1226419.

113. Luckham PF, Rossi S. The colloidal and rheological properties of bentonite suspensions. *Adv Coll Interface Sci.* 1999;82:43-92.

114. Ma R, Sasaki T. Nanosheets of oxides and hydroxides: ultimate 2D charge-bearing functional crystallites. *Adv Mater.* 2010;22: 5082-5104.

115. Osada M, Sasaki T. Two-dimensional dielectric nanosheets: novel nanoelectronics from nanocrystal building blocks. *Adv Mater.* 2012;24:210-228.

116. Golberg D, Bando Y, Huang Y, et al. Boron nitride nanotubes and nanosheets. *ACS Nano.* 2010;4:2979-2993.

117. Naguib M, Mashtalir O, Carle J, et al. Two-dimensional transition metal carbides. *ACS Nano.* 2012;6:1322-1331.

118. Cantwell PR, Tang M, Dillon SJ, Luo J, Rohrer GS, Harmer MP. Grain boundary complexions. *Acta Mater.* 2014;62: 1-48.

119. Luo J, Chiang Y-M. Wetting and prewetting on ceramic surfaces. *Annu Rev Mater Res.* 2008;38:227-249.

120. Baram M, Chatain D, Kaplan WD. Nanometer-thick equilibrium films: the interface between thermodynamics and atomistics. *Science.* 2011;332:206-209.

121. Kim S, Sinai O, Lee C-W, Rappe AM. Controlling oxide surface dipole and reactivity with intrinsic nonstoichiometric epitaxial reconstructions. *Phys Rev B.* 2015;92:235431.

122. Zhu Y, Salvador PA, Rohrer GS. Controlling the relative areas of photocathodic and photoanodic terraces on the SrTiO₃ (111) surface. *Chem Mater.* 2016;28:5155-5162.

123. Luo J. Developing interfacial phase diagrams for applications in activated sintering and beyond: current status and future directions. *J Am Ceram Soc.* 2012;95:2358-2371.

124. Harmer MP. Interfacial kinetic engineering: how far have we come since Kingery's inaugural Sosman address? *J Am Ceram Soc.* 2010;93:301-317.

125. Luo J. Stabilization of nanoscale quasi-liquid interfacial films in inorganic materials: a review and critical assessment. *Crit Rev Solid State Mater Sci.* 2007;32:67-109.

126. Orum A, Yildizhan MM, Sezen M, et al. Transmission electron microscopy of topochemical conversion interface between La₂Ti₂O₇ reactive template and perovskite product Li₀.₁₆La₀.₆₂TiO₃ electrolyte. *Solid State Ionics.* 2016;296:78-84.

127. Simon P, Gogotsi Y, Dunn B. Where do batteries end and supercapacitors begin? *Science.* 2014;343:1210-1211.

128. Guo HZ, Baker AL, Guo J, Randall CA. Cold sintering process: a novel technique for low-temperature ceramic processing of ferroelectrics. *J Am Ceram Soc.* 2016;99:3489-3507.

129. Zou X, Goswami A, Asefa T. Efficient noble metal-free (electro) catalysis of water and alcohol oxidations by zinc-cobalt layered double hydroxide. *J Am Chem Soc.* 2013;135:17242-17245.

130. Cantwell PR, Ma S, Bojarski SA, Rohrer GS, Harmer MP. Expanding time-temperature-transformation (TTT) diagrams to interfaces: a new approach for grain boundary engineering. *Acta Mater.* 2016;106:78-86.

131. Xiao X, Song H, Lin S, et al. Scalable salt-templated synthesis of two-dimensional transition metal oxides. *Nat Commun.* 2016;7:11296.

132. Ohtomo A, Hwang HY. A high-mobility electron gas at the LaAlO₃/SrTiO₃ heterointerface. *Nature.* 2004;427:423-426.

133. Geim AK, Novoselov KS. The rise of graphene. *Nat Mater.* 2007;6:183-191.

134. Bajaj S, Wang H, Doak JW, Wolverton C, Snyder GJ. Calculation of dopant solubilities and phase diagrams of X-Pb-Se (X = Br, Na) limited to defects with localized charge. *J Mater Chem C.* 2016;4:1769-1775.

135. Armiento R, Kozinsky B, Fornari M, Ceder G. Screening for high-performance piezoelectrics using high-throughput density functional theory. *Phys Rev B.* 2011;84:014103.

136. Jain A, Ong SP, Hautier G, et al. Commentary: the materials project: a materials genome approach to accelerating materials innovation. *APL Mater.* 2013;1:011002.

137. Tang M, Carter WC, Cannon RM. Diffuse interface model for structural transitions of grain boundaries. *Phys Rev B.* 2006;73:14.

138. Alloy Theoretic Automated Toolkit (ATAT) Home Page, https://www.brown.edu/Departments/Engineering/Labs/avdw/atat/, accessed 10/14/2016.
139. Atomic Simulation Environment. https://wiki.fysik.dtu.dk/ase, Accessed October 14, 2016.

140. Object Oriented Finite Element Analysis for material microstructures. http://www.ctcms.nist.gov/oof/oof3d/, Accessed October 14, 2016.

141. MOOSE Framework Open Source Multiphysics, http://moosefra mework.org, Accessed October 14, 2016.

142. Dakota: Algorithms for design exploration and simulation credibility, https://dakota.sandia.gov/content/packages, Accessed October 14, 2016.

143. Armand M, Tarascon JM. Building better batteries. *Nature*. 2008;451:652-657.

144. Lukatskaya MR, Dunn B, Gogotsi Y. Multidimensional materials and device architectures for future hybrid energy storage. *Nat Commun.* 2016;7:12647-47.

145. Lei W, Mochalin VN, Liu D, Qin S, Gogotsi Y, Chen Y. Boron nitride colloidal solutions, ultralight aerogels and freestanding membranes through one-step exfoliation and functionalization. *Nat Commun.* 2015;6:8849.

146. Sathe BR, Zou X, Asefa T. Metal-free B-doped graphene with efficient electrocatalytic activity for hydrogen evolution reaction. *Catal Sci Technol.* 2014;4:2023-2030.

147. Knaster J, Moeslang A, Muroga T. Materials research for fusion. *Nat Phys.* 2016;12:424-434.

148. Unpublished image, courtesy of Frank W. Zok.

149. Keller T. GE Reports. http://www.gereports.com/post/11903599 2715/these-space-age-ceramics-will-be-your-jet-engines/, 2015. Accessed December 31, 2016.

150. Unpublished image, courtesy of John Shaw.

151. Ellerby D, Beckman S, Irby E, Johnson SM, Gasch M, Gusman M. Materials Development and Characterization of HfB₂/SiC Ceramics For Use In Sharp Leading Edge Applications. Proceedings of the 2004 Joint Army Navy NASA Air Force Conference.

152. Van Wie DM, Drewry DG, King DE, Hudson CM. The hyper-sonic environment: required operating conditions and design challenges. *J Mater Sci.* 2004;39:5915-5924.

153. Paul A, Jayaseelan DD, Venugopal S, et al. UHTC compos-ites for hypersonic applications. *Am Ceram Soc Bull.* 2012; 91:22-29.

154. Monteverde F, Savino R, Fumo MS, Di Maso A. Plasma wind tunnel testing of ultra-high temperature ZrB₂-SiC composites under hypersonic re-entry conditions. *J Eur Ceram Soc.* 2010;30:2313-2321.

155. Squire TH, Marschall J. Material property requirements for analysis and design of UHTC components in hypersonic applications. *J Eur Ceram Soc.* 2010;30:2239-2251.

156. Bongiorno A, Fröst CJ, Kalia RK, et al. A perspective on modeling materials in extreme environments: oxidation of ultrahigh-temperature ceramics. *MRS Bull.* 2006;31:410-418.

157. Marschall J, Chamberlain A, Crunkleton D, Rogers B. Catalytic atom recombination on ZrB₂/SiC and HfB₂/SiC ultrahigh-temperature ceramic composites. *J Spacec Rockets.* 2004;41.

158. Fahrenholtz WG, Hilmas GE. Refractory diborides of zirconium and hafnium. *J Am Ceram Soc.* 2007;90:1347-1364.

159. Marshall DB, Cox BN. Integral textile ceramic structures. *Annu Rev Mater Res.* 2008;38:425-443.

160. Levine SR, Opila EJ, Halbig MC, Kiser JD, Singh M, Salem JA. Evaluation of ultra-high temperature ceramics for aero-propulsion use. *J Eur Ceram Soc.* 2002;22:2757-2767.

161. Fahrenholtz WG. Thermodynamic analysis of ZrB₂-SiC oxidation: formation of a SiC-depleted region. *J Am Ceram Soc.* 2007;90:143-148.

162. Gasch M, Johnson S. Physical characterization and arcjet oxidation of hafnium-based ultra high temperature ceramics fabricated by hot pressing and field-assisted sintering. *J Eur Ceram Soc.* 2010;30:2337-2344.

163. Poerschke DL, Novak MD, Abdul-Jabbar NM, Novak MD, Krämer S, Levi CG. Selective active oxidation in hafnium boride-silicon carbide composites above 2000°C. *J Eur Ceram Soc.* 2016;36:3697-3707.

164. Padture NP. Advanced structural ceramics in aerospace propulsion. *Nat Mater.* 2016;15:804-809.

165. Reed RC. *The Superalloys: Fundamentals and Applications.* New York: Cambridge University Press; 2006:372.

166. Perepezko JH. The hotter the engine, the better. *Science.* 2009;326:1068-1069.

167. Pollock TM, Dibbern J, Tsunekane M, Zhu J, Suzuki A. New co-based γ-γ' high-temperature alloys. *J Met.* 2010;62:58-63.

168. Zok FW. Ceramic-matrix composites enable revolutionary gains in turbine engine efficiency. *Am Ceram Soc Bull.* 2016;95:22-28.

169. Evans AG, Clarke DR, Levi CG. The influence of oxides on the performance of advanced gas turbines. *J Eur Ceram Soc.* 2008;28:1405-1419.

170. Lee KN, Fox DS, Bansal NP. Rare earth silicate environmental barrier coatings for SiC/SiC composites and Si₃N₄ ceramics. *J Eur Ceram Soc.* 2005;25:1705-1715.

171. Levi CG, Hutchinson JW, Vidal-Setif M-H, Johnson CA. Environmental degradation of TBCs by molten deposits. *MRS Bull.* 2012;37:932-941.

172. Jackson RW, Zaleski EM, Hazel BT, Begley MR, Levi CG. Response of molten silicate infiltrated Gd₂Zr₂O₇ thermal barrier coatings to temperature gradients. *Acta Mater.* 2017, in press.

173. Poerschke DL, Hass DD, Eustis S, Seward GGE, Van Sluytman JS, Levi CG. Stability and CMAS resistance of ytterbium-silicate/hafnate TBC/EBCs for SiC Composites. *J Am Ceram Soc.* 2015;98:278-286.

174. Stolzenburg F, Johnson MT, Lee KN, Faber KT. The interaction of calcium-magnesium-aluminosilicate with ytterbium silicate environmental barrier materials. *Surf Coat Technol.* 2015;284:44-50.

175. Zhao HB, Richards BT, Levi CG, Wadley HNG. Molten silicate reactions with plasma sprayed ytterbium silicate coatings. *Surf Coat Technol.* 2016;288:151-162.

176. Lee WE, Gilbert M, Murphy ST, Grimes RW. Opportunities for advanced ceramics and composites in the nuclear sector. *J Am Ceram Soc.* 2013;96:2005-2030.

177. Wirth BD, Nordlund K, Whyte DG, Xu D. Fusion materials modeling: challenges and opportunities. *MRS Bull.* 2011;36:216-222.

178. Victoria M, Baluc N, Spätig P. Structural materials for fusion reactors. *Nucl Fusion.* 2001;41:1047-1053.

179. Dubrovinskaia N, Dubrovinsky L, Solopova NA, et al. Terapascal static pressure generation with ultrahigh yield strength nanodiamond. *Sci Adv.* 2016;2:1-12.
180. Liu X, Chen X, Ma H-A, et al. Ultrahard stitching of nanotwinned diamond and cubic boron nitride in C₂-BN composite. *Sci Rep*. 2016;6:1-9.

181. Compton BG, Gamble EA, Zok FW. Failure initiation during impact of metal spheres onto ceramic targets. *Int J Impact Eng.* 2013;55:11-23.

182. Subhash G, Awasthi AP, Kunka C, Jannotti P, DeVries M. In search of amorphization-resistant boron carbide. *Scripta Mater.* 2016;123:158-162.

183. Koumoto K, Wang Y, Zhang R, Kosuga A, Funahashi R. Oxide thermoelectric materials: a nanostructuring approach. *Annu Rev Mater Res.* 2010;40:363-394.

184. Tarascon J-M. Solid oxide fuel cells for power generation. *Philos Trans: Math, Phys Eng Sci.* 2010;368:3227-3241.

185. Singhal SC. Solid oxide fuel cells for power generation. *Wiley Interdisc Rev Energy Environ.* 2014;3:179-194.

186. Kim C, Pilania G, Ramprasad R. From organized high-throughput data to phenomenological theory using machine learning: the example of dielectric breakdown. *Chem Mater.* 2016;28:1304-1311.

187. Gutfleisch O, Willard MA, Brück E, Chen CH, Sankar SG, Liu JP. Magnetic materials and devices for the 21st century: stronger, lighter, and more energy efficient. *Adv Mater.* 2011;23:821-842.

188. Norman MR. Materials design for new superconductors. *Rep Prog Phys.* 2016;79:1-9.

189. Wadsworth J, Crabtree GW, Hemley RJ. Basic research needs for materials under extreme environments. *DOE Office Basic Energy Sci.* 2008.

190. Begley MR, Hutchinson JW. *The Mechanics and Reliability of Films, Coatings and Multilayers*. New York, NY: Cambridge University Press; 2016.

191. Parthasarathy TA, Rapp RA, Opeka M, Kerans RJ. A model for the oxidation of ZrB₂, HfB₂ and TiB₂. *Acta Mater.* 2007;55: 5999-6010.

192. Jayaseelan DD, Zapata-Solvas E, Brown P, Lee WE. In situ formation of oxidation resistant refractory coatings on SiC-reinforced ZrB₂ ultra high temperature ceramics. *J Am Ceram Soc.* 2012;95:1247-1254.

193. Grant KM, Krämer S, Löfvader JPA, Levi CG. CMAS degradation of environmental barrier coatings. *Surf Coat Technol.* 2007;202:653-657.

194. Hong Q-J, Van de Walle A. Prediction of the material with highest known melting point from *ab initio* molecular dynamics calculations. *Phys Rev B.* 2015;92:1-6.

195. Cedillos-Barraza O, Manara D, Boboridis K, et al. Investigating the highest melting temperature materials: a laser melting study of the TaC-HfC system. *Sci Rep.* 2016;6:37962.

196. Rudy E. Ternary Phase Equilibria in Transition Metal-Boron-Carbon-Silicon Systems. Part V. Compendium of Phase Diagram Data. Technical Report AFML-TR-65-2, Part V., Air Force Materials Laboratory, 1969.

197. Pan Y, Zhou P, Peng Y, Du Y, Luo F. A thermodynamic description of the C-Hf–Ta system over the whole composition and temperature ranges. *CALPHAD: Comput Coupling Phase Diagrams Thermochem.* 2016;53:1-9.

198. Ivanovskii AL. Mechanical and electronic properties of diborides of transition 3d–5d metals from first principles: toward search of novel ultra-incompressible and superhard materials. *Prog Mater Sci.* 2012;57:184-228.

199. Alfe D, Gillian MJ, Price GD. The melting curve of iron at the pressures of the Earth's core from *ab initio* calculations. *Nature*. 1999;401:462-464.

200. Duff AI, Davey T, Korbmacher D, et al. Improved method of calculating ab initio high-temperature thermodynamic properties with application to ZrC. *Phys Rev B*. 2015;91:1-8.

201. Baldock RJN, Pártay LB, Bartók AP, Payne MC, Csányi G. Determining pressure-temperature phase diagrams of materials. *Phys Rev B*. 2016;93:1-9.

202. Ushakov SV, Navrotsky A. Experimental approaches to the thermodynamics of ceramics above 1500°C. *J Am Ceram Soc.* 2012;95:1463-1482.

203. Navrotsky A. Progress and new directions in calorimetry: a 2014 perspective. *J Am Ceram Soc.* 2014;97:3349-3359.

204. Krogstad JA, Gao Y, Bai J, Wang J, Lipkin DM, Levi CG. In situ diffraction study of the high-temperature decomposition of t'-zirconia. *J Am Ceram Soc.* 2015;98:247-254.

205. Sarin P, Yoon W, Jurkschat K, Zschack P, Kriven WM. Quadrupole lamp furnace for high temperature (up to 2050 K) synchrotron powder xray diffraction studies in air in reflection geometry. *Rev Sci Instrum.* 2006;77:1-9.

206. Karlsdottir SN, Halloran JW. Rapid oxidation characterization of ultra-high temperature ceramics. *J Am Ceram Soc.* 2007;90:3233-3238.

207. Carney C, Parthasarathy TA, Cinibulk MK. Separating test artifacts from material behavior in the oxidation studies of HfB₂-SiC at 2000°C and above. *Int J Appl Ceram Technol.* 2013;10:293-300.

208. Unpublished image, courtesy of Sergey Ushakov.

209. Unpublished images, courtesy of R. Wesley Jackson and Elisa M. Zaleski.

210. Manara D, Sheindin M, Heinz W, Ronchi C. New techniques for high-temperature melting measurements in volatile refractory materials via laser surface heating. *Rev Sci Instrum.* 2008;79:1-7.

211. Neuman EW, Hilmas GE, Fahrenholtz WG. Strength of zirconium diboride to 2300°C. *J Am Ceram Soc.* 2013;96: 47-50.

212. Gasch M, Johnson S, Marschall J. Thermal conductivity characterization of hafnium diboride-based ultra-high-temperature ceramics. *J Am Ceram Soc.* 2008;91:1423-1432.

213. Blumm J, Opfermann J. Thermophysical properties of silicon carbide green bodies prior to, during and after the sintering process. *High Temp/High Press.* 2003;35:513-520.

214. Harrington GJK. Effect of Solid Solutions and Second Phases on the Thermal Conductivity of Zirconium Diboride Ceramics. Ph.D. Thesis in Materials Science and Engineering, Missouri University of Science and Technology, 2014.

215. Savino R, Fumo MS, Silvestroni L, Sciti D. Arc-jet testing on HfB₂ and HfC-based ultra-high temperature ceramic materials. *J Eur Ceram Soc.* 2008;28:1899-1907.

216. Larrimbe L, Pettinà M, Nikbin K, et al. High heat flux laser testing of HfB₂ cylinders. *J Am Ceram Soc.*, 2017;100:293-303.

217. Szlufarska I, Ramesh KT, Warner DH. Simulating mechanical behavior of ceramics under extreme conditions. *Annu Rev Mater Res.* 2013;43:131-156.

218. Haboub A, Bale HA, Nasiatka JR, et al. Tensile testing of materials at high temperatures above 1700°C with in situ synchrotron X-ray micro-tomography. *Rev Sci Instrum.* 2014;85:1-13.
219. Bale HA, Haboub A, MacDowell AA, et al. Real-time quantitative imaging of failure events in materials under load at temperatures above 1,600°C. *Nat Mater.* 2013;12:40-46.

220. Shyam A, Lara-Curzio E. The double-torsion testing technique for determination of fracture toughness and slow crack growth behavior of materials: a review. *J Mater Sci.* 2006;41:4093-4104.

221. Dwivedi G, Viswanathan V, Sampath S, Shyam A, Lara-Curzio E. Fracture toughness of plasma-sprayed thermal barrier ceramics: influence of processing, microstructure, and thermal aging. *J Am Ceram Soc.* 2014;97:2736-2744.

222. Donohue EM, Philips NR, Begley MR, Levi CG. Thermal barrier coating toughness: measurement and identification of a bridging mechanism enabled by segmented microstructure. *Mater Sci Eng, A.* 2013;564:324-330.

223. Bassett WA. Diamond anvil cell, 50th birthday. *High Press Res.* 2009;29:163-186.

224. Clark AN, Lesher CE, Jacobsen SD, Sen S. Mechanisms of anomalous compressibility of vitreous silica. *Phys Rev B.* 2014;90:174110.

225. Pettinà M, Biglari F, Heaton A, Brown P, Nikbin K. Modelling damage and creep crack growth in structural ceramics at ultra-high temperatures. *J Eur Ceram Soc.* 2014;34:2799-2805.

226. Pettinà M, Harrison RW, Vandeperre LJ, et al. Diffusion-based and creep continuum damage modelling of crack formation during high temperature oxidation of ZrN ceramics. *J Eur Ceram Soc.* 2016;36:2341-2349.

227. Begley MR, Philips NR, Compton BG, Wilbrink D, Ritchie RO, Utz M. Micromechanical models to guide the development of brick and mortar composites. *J Mech Phys Solids.* 2012;60:1545-1560.

228. Parthasarathy TA, Rapp RA, Opeka MM, Cinibulk MK. Modeling oxidation kinetics of SiC-containing refractory diborides. *J Am Ceram Soc.* 2012;95:338-349.

229. Gasch M, Ellerby D, Irby E, Beckman S, Gusman M, Johnson S. Processing, properties and arc jet oxidation of hafnium diboride/silicon carbide ultra high temperature ceramics. *J Mater Sci.* 2004;39:5925-5937.

230. Marschall J, Pejakovic DA, Fahrenholtz WG, Hilmas GE, Panaei F, Chazot O. Temperature jump phenomenon during plasmatron testing of ZrB₂-SiC ultrahigh-temperature ceramics. *J Thermophys Heat Transfer.* 2012;26:559-572.

231. Marschall J, Fletcher DG. High-enthalpy test environments, flow modeling and in situ diagnostics for characterizing ultra-high temperature ceramics. *J Eur Ceram Soc.* 2010;30:2323-2336.

232. Novak MD, Zok FW. High temperature materials testing with full-field strain measurement: experimental design and practice. *Rev Sci Instrum.* 2012;82.

233. Jackson RW, Zaleski EM, Poerschke DL, Hazel BT, Begley MR, Levi CG. Interaction of molten silicates with thermal barrier coatings under temperature gradients. *Acta Mater.* 2015;89:396-407.

234. Siddiqui SF, Knipe K, Manero A, et al. Synchrotron X-ray measurement techniques for thermal barrier coated cylindrical samples under thermal gradients. *Rev Sci Instrum.* 2013;84:1-7.

235. Weyant CM, Almer J, Faber KT. Through-thickness determination of phase composition and residual stresses in thermal barrier coatings using high-energy X-rays. *Acta Mater.* 2010;58:943-951.

236. Harder BJ, Ramirez-Rico J, Almer JD, Lee KN, Faber KT. Chemical and mechanical consequences of environmental barrier coating exposure to calcium–magnesium–aluminosilicate. *J Am Ceram Soc.* 2011;94(S1):S178-S185.

237. Stolzerburg F, Kenesei P, Almer J, Lee KN, Johnson MT, Faber KT. The influence of calcium-magnesium-aluminosilicate deposits on internal stresses in Yb₂Si₂O₇ multilayer environmental barrier coatings. *Acta Mater.* 2016;105:189-198.

238. Staron P, Fischer T, Keckes J, et al. Depth-resolved residual stress analysis with high-energy synchrotron X-rays using a conical slit cell. *Mater Sci Forum.* 2014;768–769:72-75.

239. Mauro JC, Philip CS, Vaughn DJ, Pambianchi MS. Glass science in the United States: current status and future directions. *Int J Appl Glass Sci.* 2014;5:2-15.

240. Mauro JC, Zanotto ED. Two centuries of glass research: historical trends, current status, and grand challenges for the future. *Int J Appl Glass Sci.* 2014;5:313-327.

241. Schilling JS. The use of high pressure in basic and materials science. *J Phys Chem Solids.* 1998;59:553-568.

242. Grande T, Holloway JR, McMillan PF, Angell CA. Nitride glasses obtained by high-pressure synthesis. *Nature.* 1994;369:43-45.

243. Ngai KL, Capaccioli S. Impact of the application of pressure on the fundamental understanding of glass transition. *J Phys-Condens Matter.* 2008;20:244101.

244. Wondraczek L, Sen S, Behrens H, Youngman RE. Structure-energy map of alkali borosilicate glasses: effects of pressure and temperature. *Phys Rev B.* 2007;76(1).

245. Grimsditch M. Polymorphism in amorphous SiO₂. *Phys Rev Lett.* 1984;52:2379.

246. Murakami M, Bass JD. Spectroscopic evidence for ultrahigh-pressure polymorphism in SiO₂ glass. *Phys Rev Lett.* 2010;104:025504.

247. Nicholas J, Sinogeikin S, Kieffer J, Bass J. Spectroscopic evidence of polymorphism in vitreous B₂O₃. *Phys Rev Lett.* 2004;92:215701.

248. Kono Y, Kenney-Benson C, Ikuta D, Shibazaki Y, Wang YB, Shen GY. Ultrahigh-pressure polyamorphism in GeO₂ glass with coordination number > 6. *Proc Natl Acad Sci.* 2016;113:3436-3441.

249. Tsiok OB, Brazhkin VV, Lyapin AG, Khvostantsev LG. Logarithmic kinetics of the amorphous-amorphous transformations in SiO₂ and GeO₂ glasses under high pressure. *Phys Rev Lett.* 1998;80:999.

250. Zeidler A, Wezka K, Rowlands RF, et al. High-pressure transformation of SiO₂ glass from a tetrahedral to an octahedral network: a joint approach using neutron diffraction and molecular dynamics. *Phys Rev Lett.* 2014;113:135501.

251. Meng Y, Hrubiak R, Rod E, Boehler R, Shen GY. New developments in laser-heated diamond anvil cell with *in situ* synchrotron x-ray diffraction at High Pressure Collaborative Access Team. *Rev Sci Instrum.* 2015;86:072201.

252. Salmon PS, Zeidler A. Networks under pressure: the development of *in situ* high-pressure neutron diffraction for glassy and liquid materials. *J Phys-Condens Matter.* 2015;27:133201.

253. Lee SK, Eng PJ, Mao HK, et al. Probing of bonding changes in B₂O₃ glasses at high pressure with inelastic X-ray scattering. *Nat Mater.* 2005;4:851-854.
254. Lin JF, Santoro M, Struzhkin VV, Mao HK, Hemley RJ. *In situ* high pressure-temperature Raman spectroscopy technique with laser-heated diamond anvil cells. *Rev Sci Instrum.* 2004;75: 3302-3306.

255. Li FF, Cui QL, He Z, et al. Brillouin scattering spectroscopy for a laser heated diamond anvil cell. *Appl Phys Lett.* 2006;88:203507.

256. Edwards T, Endo T, Walton JH, Sen S. Observation of the transition state for pressure-induced $BO_3 \rightarrow BO_4$ conversion in glass. *Science.* 2014;345:1027-1029.

257. Storek M, Adjei-Acheamfour M, Christensen R, Martin SW, Boehmer R. Positive and negative mixed glass former effects in sodium borosilicate and borophosphate glasses studied by $^{23}$Na NMR. *J Phys Chem B.* 2016;120:4482-4495.

258. Martin SW, Bischoff C, Schuller K. Composition dependence of the $Na^+$ ion conductivity in $0.5Na_2S + 0.5[xGeS_2 + (1-x)PS_5/2]$ mixed glass former glasses: a structural interpretation of a negative mixed glass former effect. *J Phys Chem B.* 2015;119: 15738-15751.

259. Christensen R, Olson G, Martin SW. Ionic conductivity of mixed glass former $0.35Na_2O + 0.65[xB_2O_3 + (1-x)P_2O_5]$ glasses. *J Phys Chem B.* 2013;117:16577-16586.

260. Guerette M, Ackerson MR, Thomas J, et al. Structure and properties of silica glass densified in cold compression and hot compression. *Sci Rep.* 2015;5:15343.

261. Huang LP, Kieffer J. Anomalous thermomechanical properties and laser-induced densification of vitreous silica. *Appl Phys Lett.* 2006;89:141915.

262. Angell CA. Calorimetric studies of the energy landscapes of glassformers by hyperquenching methods. *J Therm Anal Calorim.* 2002;69:785-794.

263. Angell CA, Yue YZ, Wang LM, Copley JRD, Borick S, Mossa S. Potential energy, relaxation, vibrational dynamics and the boson peak, of hyperquenched glasses. *J Phys-Condens Matter.* 2003;15:S1051-S1068.

264. Kiczenski TJ, Stebbins JF. The development of a rapid quenching device for the study of the dependence of glass structure on fictive temperature. *Rev Sci Instrum.* 2006;77:013901.

265. Rouxel T, Ji H, Guin JP, Augereau F, Ruffle B. Indentation deformation mechanism in glass: densification versus shear flow. *J Appl Phys.* 2010;107:9.

266. Yuan FL, Huang LP. Brittle to ductile transition in densified silica glass. *Sci Rep.* 2014;4:5035.

267. Smedskjaer MM, Bauchy M, Mauro JC, Rzoska SJ, Bockowski M. Unique effects of thermal and pressure histories on glass hardness: structural and topological origin. *J Chem Phys.* 2015; 143:16.

268. Liebermann RC. Multi-anvil, high pressure apparatus: a half-century of development and progress. *High Press Res.* 2011;31:493-532.

269. Smedskjaer MM, Rzoska SJ, Bockowski M, Mauro JC. Mixed alkaline earth effect in the compressibility of aluminosilicate glasses. *J Chem Phys.* 2014;140:5.

270. Klement W, Willens RH, Duwez P. Non-crystalline structure in solidified gold-silicon alloys. *Nature.* 1960;187:869-870.

271. Inoue A, Zhang T, Masumoto T. Glass-forming ability of alloys. *J Non-Cryst Solids.* 1993;156:473-480.

272. Inoue A. Stabilization of metallic supercooled liquid and bulk amorphous alloys. *Acta Mater.* 2000;48:279-306.

273. Sarjeant PT, Roy R. *Reactivity of Solids*. DeVries RC, Mitchell JW, Roberts RW, Cannon P, eds. New York: John Wiley & Sons, Inc.; 1969.

274. Nassau K. Rapidly quenched glasses. *J Non-Cryst Solids.* 1980;42:423-431.

275. Ulrich DR, Smoke EJ. Devitrified barium titanate dielectrics. *J Am Ceram Soc.* 1966;49:210-215.

276. Nassau K, Cava RJ, Glass AM. The ionic-conductivity variation in rapidly quenched lithium-containing glasses. *Solid State Ionics.* 1981;2:163-170.

277. Weber JKR, Abadie JG, Hixson AD, Nordine PC, Jerman GA. Glass formation and polyamorphism in rare-earth oxide-aluminum oxide compositions. *J Am Ceram Soc.* 2000;83:1868-1872.

278. Rosenflanz A, Frey M, Endres B, Anderson T, Richards E, Schardt C. Bulk glasses and ultrahard nanoceramics based on alumina and rare-earth oxides. *Nature.* 2004;430:761-764.

279. Kaneko M, Yu JD, Masuno A, et al. Glass formation in $LaO_{3/2}-TiO_2$ binary system by containerless processing. *J Am Ceram Soc.* 2012;95:79-81.

280. Rosales-Sosa GA, Masuno A, Higo Y, et al. High elastic moduli of a $54Al_2O_3-46Ta_2O_5$ glass fabricated via containerless processing. *Sci Rep.* 2015;5:15233.

281. Watanabe Y, Masuno A, Inoue H. Glass formation of rare earth aluminates by containerless processing. *J Non-Cryst Solids.* 2012;358:3563-3566.

282. Weber R, Sen S, Youngman RE, Hart RT, Benmore CJ. Structure of high alumina content $Al_2O_3-SiO_2$ composition glasses. *J Phys Chem B.* 2008;112:16726-16733.

283. Yoshimoto K, Masuno A, Inoue H, Watanabe Y. Transparent and high refractive index $La_2O_3-WO_3$ glass prepared using containerless processing. *J Am Ceram Soc.* 2012;95:3501-3504.

284. Masuno A, Inoue H, Yu J, Arai Y. Refractive index dispersion, optical transmittance, and Raman scattering of $BaTi_2O_5$ glass. *J Appl Phys.* 2010;108:063520.

285. Rosales-Sosa GA, Masuno A, Higo Y, Inoue H. Crack-resistant $Al_2O_3-SiO_2$ glasses. *Sci Rep.* 2016;6:23620.

286. Weber JKR, Tamalonis A, Benmore CJ, et al. Aerodynamic levitator for *in situ* x-ray structure measurements on high temperature and molten nuclear fuel materials. *Rev Sci Instrum.* 2016;87:073902.

287. Mauro NA, Vogt AJ, Derendorf KS, et al. Electrostatic levitation facility optimized for neutron diffraction studies of high temperature liquids at a spallation neutron source. *Rev Sci Instrum.* 2016;87:073902.

288. Mauro JC, Tandia A, Vargheese KD, Mauro YHZ, Smedskjaer MM. Accelerating the design of functional glasses through modeling. *Chem Mater.* 2016;28:4267-4277.

289. Li N, Ching W-Y. Structural, electronic and optical properties of a large random network model of amorphous $SiO_2$ glass. *J Non-Cryst Solids.* 2014;383:28-32.

290. Henderson GS, Calas G, Stebbins JF. The structure of silicate glasses and melts. *Elements.* 2006;2:269-273.

291. Benoit M, Ispas S, Jund P, Jullien R. Model of silica glass from combined classical and *ab initio* molecular-dynamics simulations. *Eur Phys J B-Condens Matter Complex Syst.* 2000;13:631-636.

292. McGreevy R, Pusztai L. Reverse Monte Carlo simulation: a new technique for the determination of disordered structures. *Mol Simul.* 1988;1:359-367.
293. Pandey A, Biswas P, Drabold DA. Inversion of diffraction data for amorphous materials. *Sci Rep*. 2016;6:33731.

294. Kübel C, Voigt A, Schoenmakers R, et al. Recent advances in electron tomography: TEM and HAADF-STEM tomography for materials science and semiconductor applications. *Microsc Microanal*. 2005;11:378-400.

295. Huang PY, Kurasch S, Srivastava A, et al. Direct imaging of a two-dimensional silica glass on graphene. *Nano Lett*. 2012;12: 1081-1086.

**How to cite this article:** Faber KT, Asefa T, Backhaus-Ricoult M, et al. The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop. *J Am Ceram Soc*. 2017;100:1777-1803.
https://doi.org/10.1111/jace.14881