Composite materials containing a variety of elements have significant application value in many fields, and controlling the distribution of each element within the material is crucial for both the overall structure and properties of the material.

When developing bulk materials at the macro scale, researchers can generally use phase diagrams to design the material structure and element distribution.

However, when the overall size of the material is reduced to nanoscale or sub-nanoscale, macro phase diagrams may no longer be applicable.

For example, theoretical studies have shown that in nano particles of 1-10 nanometers in size, the immiscibility gap between elements can gradually decrease or even be eliminated.

But on the experimental level, there is currently no systematic and comprehensive experimental evidence in the field to answer how the size of nanomaterials affects the thermodynamic miscibility behavior between elements.Due to a lack of sufficient understanding of the thermodynamic behavior of elements at the microscale, scholars have been hindered from better designing and constructing multi-element nanomaterials with specific structures.

 

In this research context, Professor Chen Pengcheng from Fudan University and his collaborators started from the experimental perspective of "seeing is believing" and designed a binary model system to explore how the solubility of immiscible elements changes in nanoparticles of different compositions and sizes.

 

Through this, they systematically revealed the phenomenon of compatibility transformation of immiscible elements in microscale materials, and combined theoretical simulations to explain the key factors causing the transformation of element compatibility.

 

The reviewers of the relevant paper commented: "This work will change researchers' fragmented understanding of thermodynamic behavior at the nanoscale. For the first time, the author has systematically demonstrated to people the process of change in element compatibility from macro to micro with high-quality experimental data, which is of great significance for the application of nanomaterials in many fields."

 

Chen Pengcheng said that this work shows that elements that are incompatible on a macroscopic scale may actually be compatible at the microscale, thus providing new ideas for the development of multi-element nanomaterials and greatly expanding the design space.Currently, multi-component nanomaterials have been widely applied in fields such as efficient catalysis and nano optoelectronic devices. The findings of this work will provide a theoretical basis and guidance for scholars on how to better design the structure of multi-component nanomaterials.

Some materials that were previously considered to have application value but were neglected due to their instability may not actually have stability issues, and these multi-component nanomaterials still hold significant research importance.

It is reported that a few years ago, when Chen Pengcheng's postdoctoral career had just begun, after several discussions with his mentor, he decided to focus on the study of changes in elemental compatibility within nanoparticles.

Due to his previous work focusing on multi-component nanomaterials, he had some basic understanding of this direction. At the same time, after reading relevant literature, he had a preliminary assessment of the challenges that might be encountered.

This includes finding a suitable model nanoparticle system for research, preparing nanoparticles with a wide range of parameters, characterizing the thermodynamic distribution of different elements within the particles, and providing a mechanistic explanation for the thermodynamic phase behavior, etc.After determining the general direction, Chen Pengcheng began to synthesize binary nanoparticles composed of immiscible elements. During this period, many systems were screened.

Due to the research subjects being nanoparticles with ultra-small sizes and composed of incompatible elements, these two characteristics determine that such nanomaterials are not easy to synthesize, and in terms of characterization, nanoparticles are also very susceptible to the influence of the external environment.

Throughout the research process, this stage took the most time, including optimizing the synthesis of model nanoparticles with different compositions and sizes, conducting systematic electron microscopy characterization of nanoparticles, and analyzing the thermodynamic phase behavior and stability of nanoparticles.

The key experimental data were basically obtained in the early stage of this stage, but a lot of time was spent in the later period to make the entire work more systematic and comprehensive. After most of the experimental data fully confirmed the research conclusions, nearly a year was spent on in-depth theoretical exploration of the mechanism of elemental compatibility transformation.

Finally, the related paper was published in Nature Nanotechnology with the title "Complete miscibility of immiscible elements at the nanometre scale" [1], with Chen Pengcheng as the first author and Professor Yang Peidong from the University of California, Berkeley, as the corresponding author.Translating the provided text into English:

One of the challenges Chen Pengcheng encountered was how to interpret the contradictory views in the literature and the conflicts with the current work.

In the literature, many theoretical studies believe that the core-shell structure is the most stable configuration for binary immiscible systems. However, this conclusion actually conflicts with many experimental reports, including the current work. The discrepancy between the results of theoretical and experimental research has not been resolved within the field.

After nearly a year of theoretical simulation, discussion, and inability to explain, followed by more simulation, more discussion, and still no explanation, some key factors that are easily overlooked in theoretical research but unavoidable in experimental research were eventually identified.

By reasonably interpreting the differences in the conclusions of the two research paradigms, it also promoted the academic community's understanding of the thermodynamic behavior of elements at the microscale.

It is also reported that a major research challenge for multi-element nanomaterials is their vast parameter space, including element combinations, element ratios, material sizes, crystal structures, alloy phase separation, etc. This requires scholars to establish practical and effective high-throughput research methods.On the one hand, from an experimental perspective, it is necessary to build a high-throughput experimental platform and accumulate the corresponding key datasets; on the other hand, from a theoretical research perspective, AI will be a very good aid.

Based on existing datasets, AI will assist researchers in accelerating the pace of material development. Therefore, like many other experimental scientific fields, there is a need for a deep integration of experimental research and AI research, complementing each other and promoting mutual development.

It is also reported that in the team's preliminary research [2], a database-style preparation method for multi-element nanoparticles was pioneered. This method was selected as one of the top ten emerging technologies in the field of chemistry by IUPAC in 2022, opening the door to systematic research on multi-element nanosystems and receiving extensive attention and follow-up from international peers.

At present, in the field of multi-element nanomaterials, there is already a lot of work focusing on how to prepare new materials for application in the field of energy catalysis. However, in contrast, researchers have a very limited understanding of the thermodynamic behavior of multi-element systems at the microscopic scale.

This is like people discovering a new type of material with many meaningful properties, but lacking understanding of how to control such materials, what the structure-performance relationship of such materials is, and so on, which supports the underlying knowledge architecture of the entire field.In this work, the research findings have actually only revealed the tip of the iceberg of basic research on micro-scale multi-element systems, and there is still a vast space that urgently needs us to continue to explore and answer.

It is reported that Chen Pengcheng has a particular interest in basic research. Based on his previous research accumulation in micro-scale multi-element systems, he will continue to conduct in-depth exploration of the basic scientific issues in this field, and strengthen the academic community's basic scientific understanding of this field.