Lin Qisheng, Corbett John D
Department of Chemistry, Iowa State University, Ames, IA 50011, USA.
Proc Natl Acad Sci U S A. 2006 Sep 12;103(37):13589-94. doi: 10.1073/pnas.0605954103. Epub 2006 Sep 1.
The refined x-ray crystal structure of the phase Mg(27)Al(10.7(2))Zn(47.3(2)) (Pa3) establishes it as the new 2/1 Bergman-type approximant of the icosahedral quasicrystal. The primitive cubic lattice consists of condensed triacontahedral and novel prolate rhombohedral (PR) clusters. Each triacontahedron encapsulates the traditional, multiply endohedral Bergman-type clusters, and each PR encapsulates an Al(2) dimer. This phase exhibits the same long-range order as recently established for the Tsai-type Sc-Mg-Zn 2/1 approximant crystal, with substantial geometric and atomic distribution differences between the two only in the short range orders. This common feature suggests that Bergman- and Tsai-type quasicrystals may be more similar than earlier conceived. Factors germane to the formation of, and the differences between, Bergman- vs. Tsai-type 1/1 and 2/1 approximate structures are considered, including notably different distributions of the more electropositive elements.
Mg(27)Al(10.7(2))Zn(47.3(2)) (Pa3) 相的精细X射线晶体结构确定它为二十面体准晶体新的2/1型伯格曼型近似晶体。原始立方晶格由凝聚的三十面体和新型长菱形（PR）簇组成。每个三十面体包封传统的、多重内面的伯格曼型簇，且每个PR包封一个Al(2)二聚体。该相展现出与最近确定的蔡氏型Sc-Mg-Zn 2/1近似晶体相同的长程有序，两者之间仅在短程有序方面存在实质性的几何和原子分布差异。这一共同特征表明伯格曼型和蔡氏型准晶体可能比之前设想的更为相似。考虑了与伯格曼型和蔡氏型1/1及2/1近似结构的形成及其差异相关的因素，特别包括更正电性元素的不同分布。
