Schneider Matthias N, Seibald Markus, Oeckler Oliver
LMU Munich, Department of Chemistry and Biochemistry, Butenandtstrasse 5-13 (D), 81377 Munich, Germany.
Dalton Trans. 2009 Mar 21(11):2004-11. doi: 10.1039/b814000f. Epub 2009 Jan 28.
New phases with the general formula (MTe)(n)(Sb(2)Te(3))(Sb(2))(4) (n = 0, 1, 2, ; M = Ge, Ag) have been synthesized by quenching stoichiometric melts of the pure elements and subsequent annealing. These phases represent a combination of the well-known homologous series (Sb(2)Te(3))(m)(Sb(2))(k) and (GeTe)(n)(Sb(2)Te(3))(m), including substitution with Ag. Their layered crystal structures contain rocksalt-type building blocks (MTe)(n)(Sb(2)Te(3)) alternating with antimony slabs which represent sections of the A7 structure type of elementary antimony. These blocks, which are stacked along the threefold axis of the trigonal crystals, vary in size according to the composition. Powder diffraction patterns allow predictions concerning the symmetry and periodicity of the stacking sequence. Single-crystal structure refinements of the members Ge(2-x)Sb(2+x)Te(5).Sb(8) (x = 0.43; R3[combining macron]m, a = 4.258(1) A, c = 97.23(2), R = 4.38%) and Ag(x)Sb(3-x)Te(4).Sb(8) (x = 0.24; P3[combining macron]m1, a = 4.282(1) A, c = 28.638(5), R = 5.38%) reveal completely ordered superstructures with extremely long periodicities containing slabs similar to those in Ge(2)Sb(2)Te(5) and GeSb(2)Te(4), respectively, alternating with four antimony layers. According to the ternary phase diagram the phases are metastable but thermal analyses do not evidence phase separation or structural phase transformations before incongruent melting, which indicates that the structures are kinetically very stable. Although the phases are valence compounds, temperature dependence of resistance shows metallic like behaviour in the range of 300-10 K, which probably indicates degenerate semiconductivity.
通过对纯元素的化学计量熔体进行淬火并随后退火，合成了通式为(MTe)ₙ(Sb₂Te₃)(Sb₂)₄（n = 0, 1, 2；M = Ge, Ag）的新相。这些相代表了著名的同系物系列(Sb₂Te₃)ₘ(Sb₂)ₖ和(GeTe)ₙ(Sb₂Te₃)ₘ的组合，包括用Ag进行取代。它们的层状晶体结构包含岩盐型结构单元(MTe)ₙ(Sb₂Te₃)，与代表元素锑的A7结构类型片段的锑板交替排列。这些沿着三角晶体的三重轴堆叠的结构单元，其尺寸根据组成而变化。粉末衍射图谱有助于预测堆叠序列的对称性和周期性。对Ge₂₋ₓSb₂₊ₓTe₅·Sb₈（x = 0.43；R3̅m，a = 4.258(1) Å，c = 97.23(2)，R = 4.38%）和AgₓSb₃₋ₓTe₄·Sb₈（x = 0.24；P3̅m1，a = 4.282(1) Å，c = 28.638(5)，R = 5.38%）成员的单晶结构精修揭示了具有极长周期性的完全有序超结构，分别包含与Ge₂Sb₂Te₅和GeSb₂Te₄中类似的板层，与四个锑层交替排列。根据三元相图，这些相是亚稳的，但热分析未证明在不一致熔化之前存在相分离或结构相变，这表明这些结构在动力学上非常稳定。尽管这些相是价化合物，但电阻的温度依赖性在300 - 10 K范围内表现出类似金属的行为，这可能表明是简并半导体。
