Lin Qisheng, Corbett John D
Department of Chemistry, Iowa State University, Ames, Iowa 50010, USA.
J Am Chem Soc. 2007 May 30;129(21):6789-97. doi: 10.1021/ja069143x. Epub 2007 May 5.
Electronic tuning and syntheses to gain the icosahedral quasicrystal (i-QC) (Ca14.1(2)Au44.2(8)In41.7(7), e/a = 1.98) and two approximant crystals (ACs) are reported. The tuning was derived from Na2Au6In5, another cubic Mg2Zn11-type structure, for which the Fermi level (e/a = 1.77) should tune to a calculated pseudogap (e/a = 2.02) under a rigid band assumption. The 1/1 AC, Ca3Au12.2(1)In6.3(2) (e/a = 1.73), crystallizes in space group Im, with a = 15.152(2) A, Z = 8, and the 2/1 AC, Ca12.6(1)Au37.0(2)In39.6(6) (e/a = 2.01), in Pa, with a = 24.632(3) A , Z = 8. Both have substantially fixed compositions according to lattice dimensions. Structure analyses reveal that both ACs contain triacontahedral clusters as the basic building blocks at the body-centered and primitive cubic unit cell levels, respectively. Densities-of-states (DOS) analyses for the 1/1 AC structure reveal a pseudogap at e/a = 2.00, close to the point at which the i-QC was predicted and experimentally tuned. Phase relationships of the ACs and the i-QC are reported according to DTA, XRD, and temperature-dependent XRD measurements. The QC is thermodynamically metastable below approximately 500 degrees C.
报道了通过电子调谐和合成获得二十面体准晶体（i-QC）（Ca14.1(2)Au44.2(8)In41.7(7)，电子/原子比e/a = 1.98）和两种近似晶体（ACs）。这种调谐源自Na2Au6In5，它具有另一种立方Mg2Zn11型结构，在刚性带假设下，其费米能级（e/a = 1.77）应调谐到计算出的赝能隙（e/a = 2.02）。1/1的AC，Ca3Au12.2(1)In6.3(2)（e/a = 1.73），结晶于空间群Im，a = 15.152(2) Å，Z = 8；2/1的AC，Ca12.6(1)Au37.0(2)In39.6(6)（e/a = 2.01），结晶于空间群Pa，a = 24.632(3) Å，Z = 8。根据晶格尺寸，两者的组成基本固定。结构分析表明，两种ACs分别在体心立方和简单立方晶胞层面包含三十面体簇作为基本构建单元。对1/1 AC结构的态密度（DOS）分析显示在e/a = 2.00处存在一个赝能隙，接近预测和实验调谐得到i-QC的点。根据差示热分析（DTA）、X射线衍射（XRD）和变温XRD测量报道了ACs与i-QC的相关系。该准晶体在约500摄氏度以下是热力学亚稳的。
