High-entropy alloys are built from an unusual recipe: instead of relying on one dominant element with smaller additions, they combine several principal elements in comparable proportions. This chemical complexity can produce remarkable strength, toughness, resistance to heat and corrosion, and catalytic performance. Yet the same complexity that gives these materials their extraordinary properties also makes them difficult to understand at the moment their crystals are born. A new study now offers the most detailed view yet of that hidden beginning, using atomic electron tomography to reconstruct the three-dimensional structures and local chemistry of 8,160 high- and medium-entropy alloy nuclei.
The findings challenge the familiar image of crystal nucleation as a simple switch from disorder to order. In classical descriptions, atoms in a liquid or supersaturated solid are expected to gather into a small, disordered cluster and then suddenly cross a critical size at which a well-defined crystal becomes stable. The new observations instead reveal a more gradual process. Structural order is strongest at the centre of a developing nucleus, decreases progressively toward its outer region and changes together with the local chemical arrangement of atoms. Rather than behaving like miniature crystals with sharply defined surfaces, many early nuclei are diffuse, partially ordered objects with internal gradients.
Capturing these structures required an unusually demanding form of microscopy. Atomic electron tomography combines electron imaging from multiple viewing directions with computational reconstruction, allowing researchers to determine where individual atoms are located in three dimensions. Conventional microscopy often produces a two-dimensional projection or averages over many particles, concealing the subtle differences between nuclei. By resolving individual atomic arrangements across thousands of separate objects, the researchers could compare the structural and chemical features of nuclei statistically while also examining their local environments. This large dataset is particularly important for high-entropy alloys, where different elements may occupy nearby sites and influence ordering in ways that cannot be inferred from composition alone.
The central discovery is what the researchers call gradient ordering. Within an emerging nucleus, atoms near the core display the greatest degree of crystal-like structural organization. Moving outward, that order gradually weakens rather than ending at a sharply defined interface. The boundary is therefore not a clean dividing line between crystal and surrounding material; it is a transition zone in which atoms retain some organization while remaining more disordered than those in the centre. The chemical pattern follows a related trend. Local chemical order, meaning the tendency of particular elements to occupy preferred neighbouring positions or arrangements, is coupled to the structural gradient. Atomic positions and elemental preferences develop together instead of representing two independent stages.
This relationship matters because chemical complexity can alter the energy landscape of nucleation. In a conventional alloy, a limited number of dominant atomic species may make it easier to describe the emerging crystal using an average composition and a single order parameter. In a high-entropy alloy, however, each element can contribute differently to bonding, strain, diffusion and local stability. Small regions may therefore adopt distinct chemical environments before the entire nucleus reaches long-range crystal order. The observations suggest that local chemistry does not merely decorate a structure that has already formed. It helps shape where ordering begins, how it spreads and which configurations become stable as the nucleus grows.
The study also follows what happens when nuclei meet and grow together. Most of the observed nuclei coalesce with their crystal lattices nearly aligned, allowing the atomic patterns on either side of the joining region to connect with relatively little disruption. This alignment can reduce the energy and structural frustration associated with merging, potentially supporting the development of larger, more coherent grains. A minority of nuclei, however, form twin boundaries. In a twin, the atomic arrangement on one side of an interface is related to the other by a specific mirror-like crystallographic relationship. Twin boundaries can strongly influence strength, deformation and transport, so their appearance during the earliest stages of growth may help determine the properties of the final material.
To describe these results, the researchers developed a framework called the gradient nucleation pathways model. The model extends classical nucleation theory by allowing structural order to vary continuously across each nucleus. In classical theory, nucleation is often represented using a competition between the bulk energetic benefit of forming a stable crystal and the interfacial energy cost of creating a boundary between the new phase and its surroundings. That approach has been highly useful, but it generally treats the nucleus as having a relatively uniform interior separated from its environment by an interface. The new model adds spatially varying order, making it possible to represent a nucleus whose centre is crystal-like while its exterior remains diffuse and only partly organized.
This change transforms the predicted route from disorder to crystallinity. Instead of a single barrier followed by abrupt growth, the model reveals multiple intermediate states and a family of possible nucleation pathways. Some pathways can involve the gradual expansion of a highly ordered core, while others may pass through configurations in which chemical organization develops before structural order becomes fully established. The model also recovers classical nucleation theory in the sharp-interface limit. In other words, when the order gradient becomes sufficiently narrow and the nucleus behaves like a crystal with a distinct surface, the established theory emerges as a special case. This connection allows the new framework to broaden classical ideas without discarding their successful predictions.
The implications extend beyond high-entropy alloys. Nucleation controls the formation of metals, semiconductors, catalysts, ceramics, minerals and many technologically important materials, yet the earliest stages are often difficult to observe because nuclei are nanoscale, short-lived and chemically heterogeneous. A model that can account for internal gradients could help explain why materials with similar average compositions sometimes develop very different grain structures or defect populations. It may also guide strategies for controlling crystallization through temperature, cooling rate, composition, surfaces or external fields. In catalysts, for example, local chemical arrangements within tiny clusters may determine which reaction sites appear. In structural alloys, the same early choices may influence grain boundaries, twins and the resistance of the finished material to deformation.
The researchers’ atomic-scale view ultimately presents crystal growth not as a binary event, but as a continuously evolving negotiation among structure, chemistry and energy. High-entropy alloys make that negotiation especially visible because many elements and local environments compete within the same nanoscale volume. By examining thousands of nuclei rather than relying on idealized averages, the study shows that the path to crystallinity can contain gradients, intermediate states and alternative outcomes. The result is a more flexible picture of how crystals are born—one that links atomic observations to a general theoretical framework and could help scientists design materials by influencing nucleation before their final properties are locked in.
Subject of Research: Crystal nucleation and growth in high- and medium-entropy alloys
Article Title: Crystal nucleation and growth in high-entropy alloys revealed by atomic electron tomography
Article References: Yuan, Y., Moniri, S., Yang, Y. et al. Crystal nucleation and growth in high-entropy alloys revealed by atomic electron tomography. Nat. Mater. (2026). https://doi.org/10.1038/s41563-026-02727-y
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41563-026-02727-y
Keywords: High-entropy alloys, medium-entropy alloys, crystal nucleation, crystal growth, atomic electron tomography, gradient ordering, local chemical order, classical nucleation theory, twin boundaries, materials science
Tags: advanced microscopy in materials sciencealloy growth mechanismsatomic electron tomographyatomic-scale materials characterizationchallenges to classical nucleation theorycomplex alloy microstructurescrystal nucleation in alloyshigh entropy alloyslocal chemical structure in alloysnucleation process in high-entropy materialsprogression of crystal formationthree-dimensional atomic imaging
