Mrs Bulletin最新文献

This article explores the impact of grain boundary structures and compositions on the functional properties of various materials for photovoltaics, batteries, and other energy-related applications. Examples of correlative microscopy studies highlight the potential to discover structure-property relationships at grain boundaries, essential for the design of energy devices to achieve superior performance. A grain boundary transition that promotes grain growth and reduces the boundary resistance in solid electrolytes is given as an example. A key focus will be on transport phenomena at grain boundaries, including mass, thermal, electrical, and ionic transport mechanisms. These transport phenomena are directly correlated with the charge defects that lead to a buildup of electric charges and potential barriers at the grain boundaries. In addition, applied electric fields can also induce boundary transitions that can affect grain boundary transport and other properties. Finally, we demonstrate that these potential barrier heights can be tuned by modulating the chemical composition, structure, and carrier concentration of the grain boundaries.

Graphical abstract: Obtaining grain boundaries (GBs) with superior properties based on the correlation between the structure, composition, and electronic properties at the GB level.

Supplementary information: The online version contains supplementary material available at 10.1557/s43577-025-01038-y.

Abstract: Understanding and controlling structure-processing-properties-performance relationships form the central pillar of materials science and engineering. Formation of phases and evolution of material imperfections (defects) provides the two primary features of a system that enables control of these relationships. Although the impact of imperfections such as dislocations or grain boundaries on material properties has been explored quite deeply, little is known about the thermodynamic phases of the defects themselves. In recent decades, a growing appreciation for the occurrence of phase transformations of surfaces and grain boundaries has emerged. This concept of grain-boundary phase transformation and its impact on properties is at the core of this issue and introductory article. The thermodynamic fundamentals will be explained, experimental and theoretical tools to uncover grain-boundary phases and related property changes are discussed and applied to different material systems. In addition, we also want to look beyond and introduce the readers to novel findings on phase transformations of other defects, such as dislocations. In several cases, phase transformations of defects have been demonstrated to dramatically affect their properties and in turn, the overall properties of the bulk materials containing them. The additional ability to control materials properties and performance by tailoring both defect distributions and their thermodynamic phase state motivate ongoing theoretical, computational, and experimental efforts to understand and control defect phase behavior.

Graphical abstract: Grain boundary with two different phases. Properties like grain growth, conductivity, strength and fracture as well as thermal transport are impacted by grain boundary phases. Schematic created by Pankti Mehta (MPI SusMat) based on a TEM image of Lena Langenohl and atomistic grain boundary structures obtained by atomistic simulations by Tobias Brink (ref.16).

Defects are fundamental to the behavior and performance of structural materials, yet their treatment in alloy design has often been decoupled from thermodynamic considerations of phase stability. The emerging concept of "defect phases" - chemically and structurally distinct configurations at lattice defects - offers a unified framework that integrates defect chemistry, thermodynamic stability, and mechanical behavior. While grain-boundary (two-dimensional) defect phases have gained recent attention, this article expands the scope to include defect phases across all dimensionalities, with a particular emphasis on dislocations (one-dimensional) as mobile carriers of plastic deformation and sites of complex phase behavior. We discuss how point, line, and planar defects can host distinct defect phases, how these phases compete for solute atoms, and how their stability can be mapped using defect phase diagrams constructed in chemical potential space. Through selected case studies in metallic solid solutions and ordered intermetallics, including Laves, B2, and µ-phases, we illustrate how dislocation-based defect phases can influence plasticity, strengthen alloys, or even drive local transformations that modify mechanical properties. By bridging defect physics with materials thermodynamics, we advocate for a defect phase-informed design paradigm that connects atomic-scale phenomena to bulk processing and performance.

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Over the past three decades, nanoindentation has continuously evolved and transformed the field of materials mechanical testing. Once highlighted by the groundbreaking Oliver-Pharr method, the utility of nanoindentation has transcended far beyond modulus and hardness measurements. Today, with increasing challenges in developing advanced energy generation and electronics technologies, we face a growing demand for accelerated materials discovery and efficient assessment of mechanical properties that are coupled with modern machine learning-assisted approaches, most of which require robust experimental validation and verification. To this end, nanoindentation finds its unique strength, owing to its small-volume requirement, of fast-probing and providing a mechanistic understanding of various materials. As such, this technique meets the demand for rapid materials assessment, including semiconductors, ceramics, and thin films, which are integral to next-generation energy-efficient and high-power electronic devices. Here, we highlight modern nanoindentation strategies using novel experimental protocols outlined by the use of nanoindentation for characterizing functional structures, dislocation engineering, high-speed nanoindentation mapping, and accelerating materials discovery via thin-film libraries. We demonstrate that nanoindentation can be a powerful tool for probing the fundamental mechanisms of elasticity, plasticity, and fracture over a wide range of microstructures, offering versatile opportunities for the development and transition of functional materials.

Graphical abstract: Modern strategies for nanoindentation in electronic systems, functional ceramics, heterogeneous structures, and thin films.

Nanoindentation is crucial in materials science for assessing mechanical properties in submicrometer volumes, and high-speed nanoindentation mapping has evolved it from a localized measurement technique into a scanning-probe-like approach for microstructures, delivering large-area, high-resolution mechanical property maps with more than 200,000 indents in hours. Such mapping enables direct imaging of hardness and modulus variations, phase boundaries, and local deformation behaviors in materials where heterogeneity governs mechanical performance. By correlating these mechanical maps with composition, orientation, and phase data from complementary analytical techniques, deep multidimensional data sets reveal the complex interplay between structure, processing, and properties. Such data sets increasingly demand advanced statistical clustering, machine learning, and deep learning for classification, trend extraction, and phase identification. Moving forward, high-speed nanoindentation is anticipated to operate under operando conditions and advanced mechanical modalities, offering new insights into interfacial deformation, anisotropic behavior, and the broader challenges of materials design and performance.

Graphical abstract: Schematic representation of high-speed nanoindentation mapping revealing microstructural heterogeneities in mechanical response. The indenter tip rapidly probes the surface, generating property maps sensitive to features such as twinning, recrystallization, segregation, precipitates, and sintered phases. These mechanical maps can be directly correlated with crystallographic and phase information from Electron Backscatter Diffraction (EBSD) and elemental composition from Energy-Dispersive X-ray Spectroscopy (EDS). Measurements can be performed operando, i.e., under real-time and service-relevant environmental conditions (e.g., temperature, atmosphere), enabling direct analysis of structure-property-performance relationships at the microstructural scale.

A triboelectric nanogenerator (TENG) is a novel device that utilizes contact electrification and electrostatic induction to convert mechanical energy into electrical energy. Its characteristics include high energy density and flexibility, enabling self-powering of electronic devices by harvesting mechanical energy from the environment. Its applications include biomedical devices, wearable electronics, and Internet-of-Things (IoT) sensors. Despite these advantages, extracting electrical energy from TENG remains challenging due to its time-varying nature and low internal capacitance. Effective power-management techniques are essential for TENG energy-harvesting systems, yet research on dedicated integrated power-conversion methods is currently limited. Given the growing interest in TENG, a comprehensive exploration of energy-harvesting systems is critically necessary. This article synthesizes and compares current advancements in triboelectric energy-harvesting systems, emphasizing strategies to enhance output power through various power-conversion techniques. Additionally, it explores techniques employed in other energy-harvesting systems to inspire innovative approaches in TENG system design.

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Abstract: The power-conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded in 2024 the theoretical single-junction Shockley-Queisser limit of 33.7% with the perovskite/silicon tandem version. The commercialization of the technology is now a reality with the PV industry demonstrating its first commercial products. Many companies have shown excellent module reliability with most of them passing the IEC standardization (required for commercial silicon solar cells). In this article, we want to bring some light on the most intriguing question regarding the stability and reliability of PSC technology: Are we there yet? Issues on stability are still under strong investigation and research on the topic has increased exponentially in the last 10 years. Since some companies have already promised excellent reliability of their modules, with 80% retention of the initial PCE after 25 years, the following  two or three years will be crucial to demonstrate these pledges. In this work, we present an outline of the most stable PSC devices reported to date and discuss the most important strategies leading to highly stable devices.

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Supplementary information: The online version contains supplementary material available at 10.1557/s43577-025-00863-5.

Thermoelectric technology has emerged as a promising solution for direct heat-to-electricity conversion and solid-state cooling, offering great energy efficiency and environmental impact advantages. However, conventional systems predominantly rely on tellurium-based materials, which are limited by scarcity, high cost, and environmental concerns. This article focuses on tellurium-free thermoelectric modules, with an emphasis on magnesium-based alternatives, including p-type MgAgSb and n-type Mg₃(Sb, Bi)₂, which demonstrate competitive performance at operating temperatures below 300℃. By exploring recent advances in material synthesis, module fabrication, and interface engineering, we highlight the potential of these sustainable materials to achieve high thermoelectric figures of merit while reducing environmental impact. Additionally, the article assesses the performance metrics and durability of these modules and discusses emerging applications in energy harvesting, medical devices, consumer electronics, and more. Finally, we outline future research directions aimed at overcoming remaining challenges, including long-term stability and scalable manufacturing, to pave the way for the widespread adoption of tellurium-free thermoelectric technology.

Graphical abstract: Potential application scenarios of Mg-based Te-free thermoelectric technology.

Abstract: For the past 30 years, nanoindentation has provided critical insights into the microstructure-strength relationship for a wide range of materials. However, it has traditionally been limited to quasistatic testing at room temperature, which has hindered a holistic understanding of microstructurally induced deformation mechanisms and their dynamic evolution as a function of the temperature and strain rate. Over the past decade, the operational scope of nanoindentation has expanded dramatically. Temperatures up to 1100°C and strain rates as high as 10⁺⁴ s^-1 and as low as 10^-8 s^-1 have become accessible. In addition, advanced techniques allow tracking microstructural evolution and corresponding changes in mechanical behavior during deformation under extreme conditions. These advancements have transformed nanoindentation into a versatile tool for comprehensive materials characterization, enabling high-throughput investigations under multimodal conditions.

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