Unraveling Thermodynamic and Kinetic Contributions to the Stability of Doped Nanocrystalline Alloys using Nanometallic Multilayers

Abstract

Targeted doping of grain boundaries is widely pursued as a pathway for combating thermal instabilities in nanocrystalline metals. However, certain dopants predicted to produce grain‐boundary‐segregated nanocrystalline configurations instead form small nanoprecipitates at elevated temperatures that act to kinetically inhibit grain growth. Here, thermodynamic modeling is implemented to select the Mo–Au system for exploring the interplay between thermodynamic and kinetic contributions to nanostructure stability. Using nanoscale multilayers and in situ transmission electron microscopy thermal aging, evolving segregation states and the corresponding phase transitions are mapped with temperature. The microstructure is shown to evolve through a transformation at lower homologous temperatures (<600 °C) where solute atoms cluster and segregate to the grain boundaries, consistent with predictions from thermodynamic models. An increase in temperature to 800 °C is accompanied by coarsening of the grain structure via grain boundary migration but with multiple pinning events uncovered between migrating segments of the grain boundary and local solute clustering. Direct comparison between the thermodynamic predictions and experimental observations of microstructure evolution thus demonstrates a transition from thermodynamically preferred to kinetically inhibited nanocrystalline stability and provides a general framework for decoupling contributions to complex stability transitions while simultaneously targeting a dominant thermal stability regime.

Gibbs Adsorption and Zener Pinning Enable Mechanically Robust High‐Performance Bi2Te3‐Based Thermoelectric Devices

“…[40][41] Therefore, inhibiting grain growth during the sintering process for nanostructured TE materials could provide much-needed thrust in the wide-scale application of TE technology. The propensity of grain growth depends on the GB velocity (v), as described by [42]…”

Strain‐Driven Thermal and Optical Instability in Silver/Amorphous‐Silicon Hyperbolic Metamaterials

“…Our results indicate that the main driving force is the inhomogeneous elastic strain energy caused by a mismatch in thermal expansion between the metallic phase of the metamaterial and the substrate. This contribution has often been disregarded [39,47] or assumed to be homogeneous. [38] Notably, the observed instability is tightly related to the HMM design, as co-sputtered Ag/a-Si [55] thin films preserve their structural integrity in the studied temperature range.…”

“…Here, the anisotropic elastic strain energy due to thermal expansion mismatch is identified as the predominant driving force. Most previous literature on multilayer instabilities disregards this effect and treats the morphological redistribution in the context of interfacial energy minimization, including work on sputtered Ag/a-Si multilayers, [44,45] other systems with high CTE missmatch, [46][47][48] predictive models, [39,49] and reviews. [50] It should be noted that these conclusions are often based on experiments using transmission electron microscopy (TEM).…”

Triple Junction Segregation Dominates the Stability of Nanocrystalline Alloys

“…While several studies demonstrated thermally stable NC materials through alloying and subsequent GB segregation, − absent from such studies is a detailed understanding of the role of TJ solute segregation in the evolution of nanostructures and stability of NC alloys. In addition to GBs, dislocations, and point-defects, TJs are an important part of the repertoire of defects in crystalline solids.…”