Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
Inorg Chem. 2011 Nov 7;50(21):11152-61. doi: 10.1021/ic201708x. Epub 2011 Sep 27.
Ternary rare-earth zinc arsenides REZn(3)As(3) (RE = La-Nd, Sm) with polymorphic modifications different from the previously known defect CaAl(2)Si(2)-type forms, and the corresponding rare-earth cadmium arsenides RECd(3)As(3) (RE = La-Pr), have been prepared by reaction of the elements at 800 °C. LaZn(3)As(3) adopts a new orthorhombic structure type (Pearson symbol oP28, space group Pnma, Z = 4, a = 12.5935(8) Å, b = 4.1054(3) Å, c = 11.5968(7) Å) in which ZnAs(4) tetrahedra share edges to form ribbons that are fragments of other layered arsenide structures; these ribbons are then interconnected in a three-dimensional framework with large channels aligned parallel to the b direction that are occupied by La(3+) cations. All remaining compounds adopt the hexagonal ScAl(3)C(3)-type structure (Pearson symbol hP14, space group P6(3)/mmc, Z = 2; a = 4.1772(7)-4.1501(2) Å, c = 20.477(3)-20.357(1) Å for REZn(3)As(3) (RE = Ce, Pr, Nd, Sm); a = 4.4190(3)-4.3923(2) Å, c = 21.4407(13)-21.3004(8) Å for RECd(3)As(3) (RE = La-Pr)) in which M(3)As(3) layers (M = Zn, Cd), formed by a triple stacking of nets of close-packed As atoms with M atoms occupying tetrahedral and trigonal planar sites, are separated by La(3+) cations. Electrical resistivity measurements and band structure calculations revealed that orthorhombic LaZn(3)As(3) is a narrow band gap semiconductor.
三元稀土锌砷化物 REZn(3)As(3)（RE = La-Nd，Sm）和相应的稀土镉砷化物 RECd(3)As(3)（RE = La-Pr）具有不同于先前已知的缺陷 CaAl(2)Si(2)型结构的多晶型变体，通过元素在 800°C 下的反应制备而成。LaZn(3)As(3)采用新的正交结构类型（Pearson 符号 oP28，空间群 Pnma，Z = 4，a = 12.5935(8)Å，b = 4.1054(3)Å，c = 11.5968(7)Å），其中 ZnAs(4)四面体通过共享边缘形成带状结构，这些带状结构是其他层状砷化物结构的片段；然后，这些带状结构在三维框架中相互连接，沿 b 方向排列的大通道被 La(3+)阳离子占据。所有其他化合物均采用六方 ScAl(3)C(3)型结构（Pearson 符号 hP14，空间群 P6(3)/mmc，Z = 2；对于 REZn(3)As(3)（RE = Ce、Pr、Nd、Sm），a = 4.1772(7)-4.1501(2)Å，c = 20.477(3)-20.357(1)Å；对于 RECd(3)As(3)（RE = La-Pr），a = 4.4190(3)-4.3923(2)Å，c = 21.4407(13)-21.3004(8)Å），其中M(3)As(3)层（M = Zn、Cd）由密堆积的 As 原子的三重堆积形成，其中 M 原子占据四面体和三角平面位，由 La(3+)阳离子隔开。电阻率测量和能带结构计算表明，正交 LaZn(3)As(3)是一种窄带隙半导体。
