Department of Geological Sciences, Stanford University, Stanford, CA, 94305, USA.
State Key Laboratory of Nuclear Physics and Technology, Center for Applied Physics and Technology, Peking University, 100871, Beijing, China.
Nat Commun. 2019 Feb 7;10(1):622. doi: 10.1038/s41467-019-08588-1.
Atomic disordering in materials alters their physical and chemical properties and can subsequently affect their performance. In complex ceramic materials, it is a challenge to understand the nature of structural disordering, due to the difficulty of direct, atomic-scale experimental observations. Here we report the direct imaging of ion irradiation-induced antisite defects in MAX phases using double C-corrected scanning transmission electron microscopy and provide compelling evidence of order-to-disorder phase transformations, overturning the conventional view that irradiation causes phase decomposition to binary fcc-structured MX. With the formation of uniformly distributed cation antisite defects and the rearrangement of X anions, disordered solid solution γ-(MA)X phases are formed at low ion fluences, followed by gradual transitions to solid solution fcc-structured (MA)X phases. This study provides a comprehensive understanding of the order-to-disorder transformations in MAX phases and proposes a method for the synthesis of new solid solution (MA)X phases by tailoring the disorder.
材料中的原子无序会改变其物理和化学性质，并可能影响其性能。在复杂的陶瓷材料中，由于难以进行直接的原子级实验观察，因此难以理解结构无序的本质。在这里，我们使用双 C 校正扫描透射电子显微镜直接观察到 MAX 相中离子辐照诱导的反位缺陷，并提供了有序到无序相转变的有力证据，颠覆了传统观点，即辐照会导致相分解为具有二元 fcc 结构的 MX。随着阳离子反位缺陷的均匀分布和 X 阴离子的重新排列，在低离子通量下形成无序固溶体 γ-(MA)X 相，随后逐渐转变为固溶体 fcc 结构的(MA)X 相。本研究全面了解了 MAX 相中的有序到无序转变，并提出了通过调整无序来合成新型固溶体(MA)X 相的方法。
