SUPERCRITICAL AMMONIA SYNTHESIS AND CHARACTERIZATION OF FOUR NEW ALKALI METAL SILVER ANTIMONY SULFIDES - MAG(2)SBS(4) AND M(2)AGSBS(4) (M=K,RB)

摘要

Four new semiconducting quaternary antimony sulfides, KAg2SbS4 (I), K2AgSbS4 (II), RbAg2SbS4 (III), and Rb2AgSbS4 (IV) were prepared in supercritical ammonia at 160 degrees C in 4 days from the appropriate mole ratios of K2S4, K2CO3, or Rb2CO3 with Ag, Sb2S3, and S-8. Both silver-rich materials, I and III, crystallize in structure types previously observed in BaAg2GeS4 and SrCu2SnS4, respectively. However, it was determined that the space group of the latter compound was inaccurately reported in the literature. Novel structure types were obtained for II and IV. The structures of I-III contain three-dimensional anionic frameworks, either [Ag2SbS4](-) or [AgSbS4](2-), built from a variety of edge- or vertex-shared antimony sulfide and silver sulfide tetrahedra. The alkali metal cations in I and II reside in two orthogonal, intersecting channels, and in three isolated one-dimensional channels in III. Compound IV has a layered structure, with a double layer of rubidium cations separating the neighboring anionic frameworks. It is noteworthy that I-III crystallize in noncentrosymmetric space groups. The structural diversity resulting from the condensation of quite regular SbS4 and distorted AgS4 tetrahedra in these four compounds and their optical band gaps are discussed. Crystal data: (I), red polyhedron, tetragonal space group, , a = 6.886(1) Angstrom, c = 8.438(2) Angstrom, V = 400.16(9) Angstrom(3), Z = 2, and R(wR) = 0.0397(0.0335); (II), yellow plate, orthorhombic space group, Pnn2, a = 10.348(2) Angstrom, b = 10.522(2) Angstrom, c = 7.946(2) Angstrom, V = 865.2(3) Angstrom(3), Z = 4, and R(wR) = 0.0377(0.0392); (III), yellow-orange needle, trigonal space group, P3(2)21, a = 6.630(1) Angstrom, c = 16.700(2) Angstrom, V = 635.8(2) A(3) Z = 3, and R(wR) = 0.0244(0.0310); (IV), yellow polyhedron, monoclinic space group, P2(1), a = 8.229(3) Angstrom, b = 10.857(2) Angstrom c = 10.346(2) Angstrom, beta = 91.55(2)degrees, V = 924.0(4) Angstrom(3), Z = 4,and R(wR) = 0.0377(0.0405). (C) 1996 Academic Press, Inc. [References: 23]