Atomic coordination patterns in bulk materials can predict stable MXene structures, offering a new design framework that expands the 2D materials landscape beyond conventional synthesis routes.
(Nanowerk Spotlight) Designing materials at the atomic level often means navigating trade-offs. Improving one property such as electrical conductivity can weaken another, like mechanical strength or chemical stability. Two-dimensional materials offer a way to rethink this balance. With their properties shaped by just a few layers of atoms, they can be engineered with remarkable precision. Among these materials, MXenes have emerged as especially adaptable. Composed of transition metals bonded to carbon or nitrogen, they are being investigated for use in batteries, sensors, antennas, catalysis, and more.
Despite the range of applications, the field remains narrowly focused. Most MXenes developed so far share similar structural origins. They are etched from a specific family of layered solids called MAX phases, which act as precursors. While this approach has led to important discoveries, it also imposes limits. It assumes that MXenes must retain the structural logic of the template they come from, which restricts the exploration of new structural variants. The question is whether that assumption is necessary.
This limitation matters because the core of every MXene is its atomic arrangement. How metal and nonmetal atoms coordinate with each other determines the stability and performance of the material. Yet the rules governing that coordination are still poorly understood. What drives a certain structural outcome? Are there ways to predict the shape a MXene will take based on something more fundamental than its immediate precursor?
A new study in Advanced Functional Materials (“A Panoramic View of MXenes via an Atomic Coordination‐Based Design Strategy”) reframes this problem by starting not with the MAX phase but with the bulk materials that come before it. The authors focus on the coordination environments found in three-dimensional precursors, proposing that these local atomic geometries offer a more reliable basis for predicting the structure and stability of MXenes. Rather than designing from the top down using known templates, the study suggests a bottom-up view that links the structure of bulk materials directly to their two-dimensional derivatives. This approach opens a much wider set of possibilities and lays the groundwork for more systematic and predictive MXene design.
The study proposes that MXene structures can be forecast by examining the types of atomic bonding present in their three-dimensional transition metal carbide and nitride precursors. Rather than relying on MAX phases as intermediates, the authors suggest that the coordination environment in the parent bulk material offers a better predictor of what the final MXene structure will be.
Using high-throughput modeling and first-principles density functional theory, the researchers evaluated 240 different MXene structures. They examined both fluorine and oxygen-terminated surfaces, as well as non-terminated cases. Each modeled structure was traced back to one of four common bulk crystal types. These included the face-centered cubic structure, labeled B1, and three distinct hexagonal structures, labeled HX1a, HX1b, and HX2. Each of these bulk forms features a different coordination pattern. Some have octahedral coordination, where each atom is surrounded symmetrically by six neighbors. Others have trigonal prismatic coordination, where six neighbors form a three-sided prism around the central atom.
Different ways atoms are arranged in bulk materials can produce a wide range of MXene structures. This diagram shows how four common atomic patterns in 3D materials lead to new layered MXenes with unique internal shapes and thicknesses. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The study found that these coordination patterns in bulk phases closely correspond to the preferred structures of their resulting MXenes. For titanium-based systems, octahedral coordination was energetically favored. For molybdenum-based systems, the prismatic form was more stable. This trend held across multiple thicknesses, including monolayer, bilayer, and trilayer MXenes.
Each bulk phase led to two MXene variants depending on how the outermost atoms aligned with the functional groups. These functional groups, such as fluorine and oxygen, help stabilize MXenes in real environments. The study showed that surface chemistry plays a role in stability but does not override the underlying coordination preference inherited from the bulk precursor.
The authors categorized 20 unique MXene structures based on these variations in thickness and coordination sequence. This more than doubles the number of viable MXene candidates compared to what has been explored experimentally. It also provides a roadmap for identifying which coordination environments are likely to produce stable 2D structures for each transition metal.
To test whether these configurations could survive under practical conditions, the team conducted additional simulations. Phonon calculations showed that most proposed structures were dynamically stable, meaning their atomic vibrations were physically realistic. Molecular dynamics simulations at 373 kelvin demonstrated that many structures could also maintain their integrity at elevated temperatures. MXenes terminated with fluorine were generally more stable than those with oxygen, likely due to stronger metal-fluorine bonding.
The study also evaluated coordination preferences across the periodic table. By mapping how each transition metal behaves in its bulk form, the authors identified clear trends. Group III through group V elements tended to favor B1-type structures with octahedral coordination. Group VI through group VIII elements aligned more closely with HX2 structures, favoring prismatic coordination. These trends help explain the behavior of MXenes based on less-studied elements such as hafnium and rhenium. Hafnium-based MXenes were found to be most stable in B1-derived forms, while rhenium-based MXenes preferred prismatic geometries.
This predictive framework offers a new way to expand the design space for MXenes. Instead of relying on MAX phase chemistry to set the limits, researchers can now begin with the known properties of bulk compounds and anticipate which coordination environments will yield stable, synthesizable 2D materials.
The implications extend beyond MXenes themselves. The coordination-based strategy could be applied to other classes of two-dimensional materials including borides, sulfides, and phosphides. Each of these also involves transition metals and shares structural features that can be interpreted through coordination analysis. The method is also suitable for machine learning approaches. Atomic coordination is a clear and interpretable variable that can be used to train algorithms to predict material properties or synthesis outcomes.
Finally, the coordination environment was found to influence not just structural stability but also mechanical properties. Titanium-based MXenes with octahedral coordination showed higher stiffness and elastic modulus values. Molybdenum-based MXenes performed better when structured with prismatic coordination. These observations demonstrate how a seemingly small change in atomic geometry can produce significant shifts in material behavior.
The study offers a systematic and evidence-driven approach to designing MXenes from first principles. By shifting the design focus away from conventional precursors and toward the atomic architecture of bulk materials, it lays the foundation for a much broader exploration of two-dimensional systems. It provides the structural logic needed to link three-dimensional compounds to their layered counterparts and equips researchers with the tools to predict which new materials are worth pursuing.
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