title: Quaternary arsenides AM(1.5)Tt(0.5)As2 (A = Na, K, Rb; M = Zn, Cd; Tt = Si, Ge, Sn): size effects in CaAl2Si2- and ThCr2Si2-type structures.
abstract: Ten quaternary arsenides AM(1.5)Tt(0.5)As2 (A = Na, K, Rb; M = Zn, Cd; Tt = Si, Ge, Sn) have been prepared by stoichiometric reactions of the elements at 600-650 °C. Seven of them (NaZn(1.5)Si(0.5)As2, NaZn(1.5)Ge(0.5)As2, NaZn(1.5)Sn(0.5)As2, NaCd(1.5)Sn(0.5)As2, KZn(1.5)Sn(0.5)As2, KCd(1.5)Sn(0.5)As2, RbCd(1.5)Sn(0.5)As2) adopt the trigonal CaAl2Si2-type structure (Pearson symbol hP5, space group P3m1, Z = 1, a = 4.0662(3)-4.4263(7) Å, c = 7.4120(5)-8.4586(14) Å), whereas the remaining three (KZn(1.5)Si(0.5)As2, KZn(1.5)Ge(0.5)As2, RbZn(1.5)Ge(0.5)As2) adopt the tetragonal ThCr2Si2-type structure (Pearson symbol tI10, space group I4/mmm, Z = 2, a = 4.0613(10)-4.1157(5) Å, c = 14.258(3)-14.662(2) Å). Both structure types contain anionic [M(1.5)Tt(0.5)As2] slabs that are built from edge-sharing tetrahedra and that stack alternately with nets of A cations. A structure map delineates the formation of these structure types for AM(1.5)Tt(0.5)As2 as a function of simple radius ratios. Although these arsenides have charge-balanced formulations, band structure calculations on NaZn(1.5)Tt(0.5)As2 (Tt = Si, Ge, Sn) indicate that semimetallic behavior is predicted as a result of overlap of the valence and conduction bands.
authors: Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
authors: Mansura
authors: M
authors: Khatun
authors: Stanislav S
authors: SS
authors: Stoyko
authors: Arthur
authors: A
authors: Mar