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Small methods: new progress in chemical potential control of metastable nanocrystalline growth

wallpapers News 2020-09-02
In the field of solid nanocrystals

has many kinds of thermodynamic metastable states (such as nanocrystals with high surface energy nanocrystals with different crystal phases twin nanocrystals) besides thermodynamic stable states. Unfortunately up to now most of these thermodynamically metastable inorganic nanocrystals were found by accident or synthesized by trial error. Although there are some regular conclusions based on the apparent experimental phenomena the growth mechanism of metastable nanocrystals is still not well understood. Recently Professor Xie Zhaoxiong Professor Kuang Qin of School of chemistry chemical engineering of Xiamen University have made important progress in clarifying the key factors that determine the metastable nanocrystalline structure in the process of crystal growth. Relevant research results were published in small methods (DOI: 10.1002 / SMTD. 202000447) with the title of "tailoring the chemical potential of crystal growth units to tune the bulk structure of nanocrystals".

about 100 years ago with the Gibbs Thomson formula (Δ μ = 2S ν / γ) people can know the relationship between the growth unit supersaturation (Δ μ) the grain size (γ). In fact this formula actually reflects the energy transfer between the growth unit (solute) the newly formed solid phase in the ideal state (constant temperature pressure). Re combing the Gibbs free energy change of crystallization process in ideal state DG = mldnl mcdnc SDS = 0 we can see that when only one kind of nanocrystal with specific bulk structure is formed that is MC is constant solute with high chemical potential (mldnl) can transfer its excess energy to the surface energy (SDS) of newly formed crystal. Based on this we have proposed to regulate the surface energy (SDS) of nanocrystals by adjusting the supersaturation (ML – MC) of crystal growth units. That is to say high supersaturation of growth units can induce the formation of nanocrystals with high surface energy a series of experiments have verified the universality of this strategy. In previous studies

only involved the growth of nanocrystals with specific bulk structure (MC is constant). In this study Professor Xie Zhaoxiong's research group further proposed that metastable nanocrystals with different bulk structures may appear in the products which means that the nuclei in the crystallization nucleation stage have different MC. Therefore it can be inferred that the chemical potential (ML) of the growth unit can adjust not only the surface structure (surface energy) of the product but also the bulk structure of the product especially in the nucleation stage. Therefore by simply changing the material of reaction vessel (hydrophobic PTFE hydrophilic glass) to control the critical chemical potential of crystal nucleation the team successfully realized the transformation of Pt PD nanocrystals from pentahedral icosahedron to single crystal cube or octahedron. The results show that the growth units with high chemical potential tend to produce high chemical potential nuclei in the nucleation stage. This study not only improves the growth theory of nanocrystals in non thermodynamic equilibrium state but also can be used to guide the controllable synthesis of nanocrystals with different thermodynamic metastable states. Dr. Zhang Jiawei of Xiamen University is the first author. The research work is supported by the key R & D projects of the Ministry of science technology the key projects of the National Natural Science Foundation of China the innovation group projects general projects.


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