Annual Review of Materials Research - Early Publication

Doped and mixed oxides are a class of materials with widespread applications, ranging from electronics to energy storage. The precise determination of ion valency in these materials is crucial for understanding their electronic, ionic, magnetic, and other properties, as well as controlling behaviors during processing and microstructure development. In this review, we present magnetometry measurement as a powerful tool to determine ion valency and position in doped and mixed oxides. Focus is given to transition metals in dilute concentrations. We discuss the theoretical framework, experimental techniques, data analysis methods, and case studies that showcase the effectiveness of magnetometry in elucidating the valency of ions in various oxide systems. The results highlight the importance of magnetometry as a nondestructive and highly sensitive technique for characterizing the valence states and positions of dopant ions. They position magnetometry as a valuable member of the suite of complementary advanced tools for characterizing ion valency.

It has long been assumed that all matter will adopt simple closed-packed lattices and become metallic under pressure, in accordance with the Thomas–Fermi–Dirac (TFD) model. However, this model struggles to explain pressure-driven complex structural transitions that have been observed in elements, including sodium, challenging our conventional understanding of compressed matter. Moreover, in stark contrast to the TFD model, first-principles calculations suggest that various elements and compounds become electrides under pressure. Electrides, characterized by concentrations of charge density at interstitial regions, can be thought of as ionic compounds where electrons behave as the anions. Though ambient-pressure molecular electrides have been extensively studied via experiments and computations, high-pressure electrides (HPEs) are not well-understood. The identification and characterization of HPEs have been, to date, based purely on theory, including topological analysis of the electron density and the electron localization function. Here, we review these theoretical analysis tools and suggest guidelines that can be used to classify systems as electrides. Moreover, we describe models used to rationalize the electronic structure of HPEs, drawing parallels with ambient-pressure molecular systems, and encourage the development of experimental techniques that provide evidence for the theoretically calculated charge localization.

Resonant soft X-ray scattering (RSoXS) is a powerful tool for chemically and orientationally resolved nano-to-mesoscale characterization of complex molecular materials. Through its development over the past 15 years, its use has been extended to uniquely characterize structures, not only dry, thin films for devices, coatings, photolithography, and liquid crystalline ordering, but also solvated nanostructures in biology for therapeutics and hydrated membranes for filtration or biosensing. Here, we review progress in this exciting and maturing technique with an eye toward the materials scientist or engineer who has little experience with RSoXS but would like to know more about how the technique would fit into their toolset.

The evolution of ferroelectric devices is driven by advancements in materials science, device physics, and engineering. However, depolarization fields and interfacial disorder limit the scaling performance, endurance, and reliability of conventional thin-film ferroelectrics. van der Waals (vdW) ferroelectric materials exhibiting novel properties at the atomic scale are interesting candidates for mitigating the aforementioned issues, thereby allowing for improved ferroelectric device performance. In this review, we discuss the unconventional origins of both spontaneous and artificial polarization, along with their associated switching mechanisms, in polar and nonpolar vdW ferroelectric crystals and heterostructures. Recent device architectures utilizing vdW ferroelectricity are reviewed with a specific focus on emerging memory, steep-slope logic, and in-memory computing applications. We conclude with an overview of the opportunities and challenges for vdW ferroelectrics related to scalability, endurance, device integration, and growth, highlighting recent advances toward manifesting next-generation electronics.

In the rapidly evolving rechargeable battery market, various applications lead to varied property requirements. One area that is emerging as essential is high-power batteries. These are expected to be able to charge and discharge in the order of minutes (slower than supercapacitors but faster than typical Li-ion batteries) and still have a high energy density (orders of magnitude higher than that of supercapacitors but lower than that of high-energy Li-ion batteries). In this space, anodes operating at a safe potential (near 1.5 V versus Li) sacrifice some energy density but enable fast cycling and lead to very safe batteries. In this review, we explore the plethora of materials being considered in the literature as potential high-power anodes. Though Nb-based anodes are prominent due to their recent popularity in the literature, any material classes leading to the appropriate balance of power and energy are discussed. We, in particular, aim to distinguish materials that are suitable only for supercapacitors from those with the potential for practical batteries, distinguished by volumetric energy density. The best materials discussed herein show excellent specific capacities and fast cycling performance, though a greater focus on performance at practical loadings is generally required.

From a microstructural standpoint, chocolate is a suspension of solid particles—including cocoa solids, sugar crystals, and sometimes milk solids—in a continuous lipid (cocoa butter) phase. The proportions and types of ingredients dictate the melting profile and rheology of the chocolate, which in turn have significant implications for its physical and sensory properties. In this review, we discuss the effects of ingredients and processing on the microstructural, rheological, and sensory properties of chocolate. Applicable rheological models are covered, as well as a brief overview of bloom. Finally, we suggest directions for future research.

The characterization of archaeological ceramics involves mineral composition studies of the ceramic mass and investigations of associated organic residues. Analyses of the mineral composition of the ceramic mass are conducted to determine the origin of the raw materials, the production technologies used to create the ceramic, and the history of the objects. Contemporary ceramics research pays much attention to analyzing organic residues, which provide valuable information about the diet, cooking practices, and vessel use of ancient communities. This article discusses examples of the use of various analytical techniques, with particular emphasis on spectroscopic and chromatographic methods. The crucial importance of validating research methods and interdisciplinary cooperation is also discussed.