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Issue 11, 2009
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A new series of long-range ordered metastable phases in the system M–Sb–Te (M = Ge, Ag)

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Abstract

New phases with the general formula (MTe)n(Sb2Te3)(Sb2)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 (Sb2Te3)m(Sb2)k and (GeTe)n(Sb2Te3)m, including substitution with Ag. Their layered crystal structures contain rocksalt-type building blocks (MTe)n(Sb2Te3) 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 Ge2−xSb2+xTe5·Sb8 (x = 0.43; R[3 with combining macron]m, a = 4.258(1) Å, c = 97.23(2), R = 4.38%) and AgxSb3−xTe4·Sb8 (x = 0.24; P[3 with combining macron]m1, a = 4.282(1) Å, c = 28.638(5), R = 5.38%) reveal completely ordered superstructures with extremely long periodicities containing slabs similar to those in Ge2Sb2Te5 and GeSb2Te4, 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.

Graphical abstract: A new series of long-range ordered metastable phases in the system M–Sb–Te (M = Ge, Ag)

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Publication details

The article was received on 12 Aug 2008, accepted on 01 Dec 2008 and first published on 28 Jan 2009


Article type: Paper
DOI: 10.1039/B814000F
Citation: Dalton Trans., 2009, 2004-2011
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    A new series of long-range ordered metastable phases in the system M–Sb–Te (M = Ge, Ag)

    M. N. Schneider, M. Seibald and O. Oeckler, Dalton Trans., 2009, 2004
    DOI: 10.1039/B814000F

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