Disordered Structures of the TM−Mg−Zn 1/1 Quasicrystal Approximants (TM = Hf, Zr, or Ti) and Chemical Intergrowth
作者:Cesar Pay Gómez、Satoshi Ohhashi、Akiji Yamamoto、An Pang Tsai
DOI:10.1021/ic800874u
日期:2008.9.15
The structures of three quasicrystal approximant phases in the TM-Mg-Zn (TM = Hf, Zr, Ti) systems with the analyzed compositions Hf5Mg18Zn77, Zr5Mg18Zn77, and Ti5.5Mg17.5Zn77 have been synthesized, and their structures have been analyzed by single-crystal X-ray diffraction. The structure analyses revealed that these cubic phases with the space group Pm contain two different rhombic-triacontahedral clusters. These clusters are so-called Bergman-type atomic clusters and previously known approximants of face-centered icosahedral (F-type) quasicrystals are composed only of Mackay-type clusters, thus these compounds are seen as new prototype structures. Electron density maps calculated by the maximum entropy method (MEM) show that one of the atomic clusters displays characteristic structural disorder. The disorder in these phases is related to the chemical intergrowth of different Friauf polyhedra, and the prospects of new guide lines for finding quasicrystals composed of such polyhedra are discussed.
Synthesis, properties and crystal structure of Zr6Zn23Si with “filled” Th6Mn23 type structure
作者:Xue-an Chen、Wolfgang Jeitschko、Martin H. Gerdes
DOI:10.1016/0925-8388(95)01967-7
日期:1996.2
the Si atoms are situated at octahedral voids of that structure formed by the Zr atoms. Thus the atomic positions of Zr 6 Zn 23 Si correspond to those of Sc 11 Ir 4 (i.e. Sc 6 Sc 16 Ir 7 Ir). Various void positions of these structures correspond to hydrogen sites in previously reported rareearth (R) transitionmetal (T) hydrides R 6 T 23 H 75 − x .
摘要 通过锆锌合金与硅的固相反应制备了新型化合物Zr 6 Zn 23 Si。它是弱抗磁性的,这被解释为泡利顺磁性,它被核心抗磁性过度补偿。其晶体结构已由单晶衍射仪数据确定:Fm 3 m ,a = 1238.5(1) pm,Z = 4,R = 0.022,215 个结构因子和 17 个可变参数。Zr和Zn原子占据Th 6 Mn 23 中Th和Mn原子的位置,而Si原子位于由Zr原子形成的结构的八面体空隙处。因此,Zr 6 Zn 23 Si 的原子位置对应于Sc 11 Ir 4 (即Sc 6 Sc 16 Ir 7 Ir) 的原子位置。