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Abstract Advances in solid-state ionic materials theory, synthesis, characterization, and simulation over the past century have enabled development of quantitative frameworks and descriptors to describe defect populations, transport, and interfacial reactions that approximate observable behavior in dilute, crystalline compositions near equilibrium. Increasing development of nondilute, disordered, or extended-defect-laden materials, and new operating conditions further from equilibrium, particularly in emerging energy, manufacturing, and information contexts, motivate development of new theoretical frameworks. This article provides an overview of computational and experimental advances in understanding defect-mediated behavior in ionic materials for batteries, fuel/electrolysis cells, sensors, thermochemical reactors, artificial synapses, ionic nanomanufacturing, and related technologies. Topics include: (1) point defects in nondilute and complex solid-solution systems, (2) point-defect populations and transport in and near extended defects, (3) defect equilibria and mobility in the excited state, (4) developing theories for ionic transport, including high-field effects and dynamic descriptors, and (5) emerging descriptors for surface reaction kinetics at intermediate-high temperatures. Graphical Abstract 

Defects and reconstructions in two-dimensional (2D) moiré materials cause out-of-plane deformations that strongly modify their electronic properties but are difficult to experimentally access. Here, we solve the 3D atomic coordinates of twisted bilayer WSe₂with picometer-scale accuracy using multislice electron ptychography (MEP) acquired from a single orientation. The resulting atomic models individually visualize each of the six atomic planes, revealing the curvature of each WSe₂layer, variations in the interlayer spacing, and the 3D locations of individual vacancies, which lie exclusively in the outer Se planes. We also observe an unexpected type of structural disorder consisting of mixed bending- and breathing-type moiré-induced corrugations that should strongly affect the emergent electronic properties. Broadly, our methods generate 3D atom-by-atom models of a 2D heterointerface from data acquired in about 30 seconds, methods that should unlock routine access to 3D atomic information in 2D systems and catalyze design methods to control out-of-plane deformations. 

New high-throughput search strategies based on statistical identification of promising chemical subspaces show potential for accelerating half-Heusler thermoelectric materials discovery.