Search of new type of stable icosahedral quasicrystals and study on their structural and physical properties

从Zn_（17）Sc_3型准晶开始，在许多Zn基和Cu基合金中发现了新的二十面体准晶：Zn-（Mg，Mn，Fe，Co，Ni，Cu，Pd，Ag，Pt，Au）-Sc，Zn-Mg-Yb和Cu-Ga-Mg-Sc，这些新准晶属于P型准晶，与Cd基和Ag-In基准晶具有结构相似性。其中Zn-（Mg，Fe，Co，Ni，Pd，Ag）-Sc和Cu-Ga-Mg-Sc是化学稳定的，并表现出非常高的结构完整性。所有这些准晶，在本报告中称为蔡型，具有共同的性质如下：基本金属是二价或有效的二价，即Zn，Cd，Cu-Ga和Ag-In。它们进一步包括约15 at.%三价Sc或镧系金属以及二价Ca或Yb。除Cd-Yb和Cd-Ca二元稳定准晶外，少量第三组分的加入对稳定准晶结构起决定性作用。这些准晶中的取代关系表明了Hume-Rothery规则在蔡型准晶形成中的重要作用。

Starting from Zn17Sc3-type approximant crystals, new icosahedral quasicrystals have been discovered in many Zn-based and Cu-based alloys : They are Zn-(Mg,Mn,Fe,Co,Ni,Cu,Pd,Ag,Pt,Au)-Sc, Zn-Mg-Yb and Cu-Ga-Mg-Sc. These new quasicrystals belong to P-type and have structural similarity to the Cd-based and the Ag-In-based quasicrystals. Among them Zn-(Mg,Fe,Co,Ni,Pd,Ag)-Sc and Cu-Ga-Mg-Sc, are thermodynamically stable and exhibit very high degree of structural perfection. All these quasicrystals, called Tsai-type in this report, have common properties as follows : The base metals are divalent or effectively divalent, namely Zn, Cd, Cu-Ga and Ag-In. They further include approximately 15 at.% of trivalent Sc or lanthanoid metals as well as divalent Ca or Yb. Addition of few percent of the third component has decisive role for stabilizing the quasicrystal structures except for the cases of binary stable quasicrystals, Cd-Yb and Cd-Ca. The substitution relationship in these quasicrystals indicates the important role of Hume-Rothery rule for the formation of Tsai-type quasicrystals.