Institute of Physical Chemistry, University of Vienna, Währingerstrasse 42, A-1090, Wien, Austria.
Dalton Trans. 2012 Feb 28;41(8):2296-303. doi: 10.1039/c1dt11972a. Epub 2011 Dec 20.
The crystal structures of three Al-rich compounds have been solved from X-ray single crystal diffractometry: τ(1)-MoPd(2-x)Al(8+x) (x = 0.067); τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) and τ(9)-ZrCu(1-x)Al(4) (x = 0.144). τ(1)-MoPd(2-x)Al(8+x) adopts a unique structure type (space group Pbcm; lattice parameters a = 0.78153(2), b = 1.02643(3) and c = 0.86098(2) nm), which can be conceived as a superstructure of the Mo(Cu(x)Al(1-x))(6)Al(4) type. Whereas Mo-atoms occupy the 4d site, Pd(2) occupies the 4c site, Al and Pd(1) atoms randomly share the 4d position and the rest of the positions are fully occupied by Al. A Bärnighausen tree documents the crystallographic group-subgroup relation between the structure types of Mo(Cu(x)Al(1-x))(6)Al(4) and τ(1). τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) has been confirmed to crystallize with the ThMn(12) type (space group I4/mmm; lattice parameters a = 0.85243(2) and c = 0.50862(3) nm). In total, 4 crystallographic sites were defined, out of which, Zr occupies site 2a, the 8f site is fully occupied by Cu, the 8i site is entirely occupied by Al, but the 8j site turned out to comprise a random mixture of Cu and Al atoms. The compound τ(9)-ZrCu(1-x)Al(4) (x = 0.144) crystallizes in a unique structure type (space group P4/nmm; lattice parameters a = 0.40275(3) and c = 1.17688(4) nm) which exhibits full atom order but a vacancy (14.4%) on the 2c site, shared with Cu atoms. τ(9)-ZrCu(1-x)Al(4) is a superstructure of Cu with an arrangement of three unit cells of Cu in the direction of the c-axis. A Bärnighausen tree documents this relationship. The ZrCu(1-x)Al(4) type (n = 3) is part of a series of structures which follow this building principle: Cu (n = 1), TiAl(3) (n = 2), τ(5)-TiNi(2-x)Al(5) (n = 4), HfGa(2) (n = 6) and Cu(3)Pd (n = 7). A partial isothermal section for the Al-rich part of the Mo-Pd-Al system at 860 °C has been established with two ternary compounds τ(1)-MoPd(2-x)Al(8+x) and τ(2) (unknown structure). The Vickers hardness (H(v)) for τ(1) was found to be 842 ± 40 MPa.
三种富铝化合物的晶体结构已通过 X 射线单晶衍射法确定：τ(1)-MoPd(2-x)Al(8+x)（x = 0.067）；τ(7)-Zr(Cu(1-x)Al(x))(12)（x = 0.514）和 τ(9)-ZrCu(1-x)Al(4)（x = 0.144）。τ(1)-MoPd(2-x)Al(8+x)采用独特的结构类型（空间群 Pbcm；晶格参数 a = 0.78153(2)，b = 1.02643(3) 和 c = 0.86098(2)nm），可被视为 Mo(Cu(x)Al(1-x))(6)Al(4)型的超结构。Mo 原子占据 4d 位，Pd(2)占据 4c 位，Al 和 Pd(1)原子随机共享 4d 位，其余位置完全被 Al 占据。Bärnighausen 树记录了 Mo(Cu(x)Al(1-x))(6)Al(4)和 τ(1)结构类型之间的晶体学群-子群关系。τ(7)-Zr(Cu(1-x)Al(x))(12)（x = 0.514）已被证实为具有 ThMn(12)型（空间群 I4/mmm；晶格参数 a = 0.85243(2)和 c = 0.50862(3)nm）的晶体。总共定义了 4 个晶体学位置，其中 Zr 占据 2a 位，8f 位完全被 Cu 占据，8i 位完全被 Al 占据，但 8j 位则由 Cu 和 Al 原子的随机混合物组成。化合物 τ(9)-ZrCu(1-x)Al(4)（x = 0.144）在独特的结构类型（空间群 P4/nmm；晶格参数 a = 0.40275(3)和 c = 1.17688(4)nm）中结晶，其具有完全的原子有序，但在 2c 位上存在空位（14.4%），与 Cu 原子共享。τ(9)-ZrCu(1-x)Al(4)是 Cu 的超结构，其在 c 轴方向上排列有三个 Cu 单元晶胞。Bärnighausen 树记录了这种关系。ZrCu(1-x)Al(4)型（n = 3）是遵循该构建原理的一系列结构的一部分：Cu（n = 1）、TiAl(3)（n = 2）、τ(5)-TiNi(2-x)Al(5)（n = 4）、HfGa(2)（n = 6）和 Cu(3)Pd（n = 7）。在 860°C 下建立了 Mo-Pd-Al 系统富铝部分的部分等温截面，其中包含两个三元化合物 τ(1)-MoPd(2-x)Al(8+x)和 τ(2)（未知结构）。发现 τ(1)的维氏硬度（H(v)）为 842 ± 40MPa。
