十面体准晶及相关晶体近似相结构本征构建单元的研究

As well known, the structure of a quasicrystal and that of its related crystalline approximant can be characterized as arrangement of atom clusters in a quasiperiodic way and in a periodic one, respectively. Nevertheless, for almost all of quasicrystals discovered to date, no model is available to account for construction of their quasiperiodic structures in view of real-space growth. As for a crystalline approximant, its structure can be subdivided into many quite small fragments by in-growth phason defects of high density where unit cell is no longer adequate to be present. It is therefore essential to clarify what kinds of characteristic building blocks are the intrinsic building units (IBUs) which are intrinsically favorite for constructing characteristic structures of quasicrystals and of crystalline approximants, respectively, since these are still open questions. This research project is to characterize IBUs for constructing decagonal quasicrystals and their structurally-related crystalline approximants in Al-Pd-TM (TM=Mn,Fe,Cr,Co) alloys of a typical quasicrystal-forming series. HREM and HAADF electron microscopy techniques will be applied to study structural features of decagonal quasicrystals and their crystalline approximants in both equilibrium and non-equilibrium structural states, through which the structural features for IBUs, together with their growth linkage relationships with the neighboring units, will be determined. Special effort will be made to reveal at atomic resolution level the highly-faulted structures in states of growth and structural transition for those quasicrystals and crystalline approximants. According to characteristics of IBUs revealed by experimental observations, growth processes of quasiperiodic structures constructed by packing of IBUs will be modeled with the aid of Monte Carlo simulation. The research work in these aspects will provide essential information for understanding formation processes of both quasicrystals and their crystalline approxiamnts, and for clarifying formation mechanisms of phason defects in them as well.

众所周知，准晶和相关晶体近似相的结构分别可以描述为由准周期和周期方式排列的原子团构成。然而对于已被发现的绝大多数准晶而言，现有的准晶模型仍无法对其准周期结构的实空间形成给出满意的解释。同样，对晶体近似相而言，其结构也会因高密度phason型生长缺陷的存在而失去用单胞描述的基础。可以说，搞清什么是构建准晶及相关近似相特征结构的本征构建单元是一个尚待解决的重要问题。本研究项目针对准晶形成合金中具有代表性的Al-Pd-(Mn,Fe,Cr,Co)系列，利用先进电子显微技术、对其中各种处于生长及相过渡状态的十面体准晶以及相关晶体近似相进行原子分辨层次上的细致表征，旨在确立相应准晶和近似相的本征构建单元以及其生长关联模式，并在此基础上，通过Monte Carlo模拟构建准周期结构的生长模型。这些研究的开展对理解准晶及相关近似相形成的过程、进而理解其中phason型缺陷的形成机制都具有重要意义。

搞清什么是准晶及相关晶体近似相的本征构建单元、并在此基础上理解实空间准周期结构的形成以及各种特殊缺陷的结构本质是长期存在的尚待解决的重要问题。本研究针对准晶形成合金中具有代表性的Al-Pd-(Mn,Fe,Cr,Co)系列以及Al-Ni-Ru合金，利用电子显微表征技术、对处于生长及各种非平衡过渡状态的十面体准晶以及相关晶体近似相的结构与缺陷特征进行了研究，取得的主要结果如下。. 在对十次Al-Pd-Mn准晶广域准周期生长结构的研究中，提出了对其定量分区分析的新方法，从而清楚地揭示出其长程准周期结构具有不同phason缺陷特征的复合共生特点。这种方法对定量分析广域准周期结构十分便捷有效。. 分别从单纯实空间生长单元排列以及实空间配合高维空间投影辅助出发，对Al-Pd-Mn十次准周期结构的形成进行了模拟生长, 获得了与实际观察准周期结构具有相同Linear Phason Strain缺陷属性的长程准周期结构。而在实空间生长模拟中采用的生长单元拼接法的生长结果可以反映无Linear Phason Strain缺陷的Al-Pd-Mn准周期结构特征。. 在基于本征构建单元的新型构建框架下，对十次准晶近似相ξ-Al-Ni-Rh以及ε16-Al-Pd-Fe中实际观察到的metadislocation缺陷进行了分析，从而清楚地揭示了此类特殊缺陷的存在特征及结构本质。 . 在对包含多种复杂合金相的Al75Pd15Fe10非平衡凝固合金组织的研究发现，经过包晶反应在O-Al13Fe4初生相周围形成一层缺陷准晶层后发生了相图中未见的共晶反应，其结果导致形成一种由M-Al13Fe4和缺陷ε16相组成的层状结构。在随后热处理形成的富Pd区发现了一种新的复杂合金相结构，其具有与ε16相同的结构单元。. 在对Al-Pd-Fe 以及Al-Pd-Co复杂合金相在常温纳米压痕塑性变形结构的研究中，揭示了其变形过程以变形带的形成与不同密度的分布为主要特征，指出局域在变形带的变形过程可能包括多种变形机制的复合。