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Polytypism of LiSr2Ge3 and the Solid Solutions LiSr2SixGe3–x and LiSr2–xEuxGe3 (0 < x < 1)

Authors

  • Qinxing Xie,

    1. Laboratorium für Anorganische Chemie, Eidgenössische Technische Hochschule, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
    2. School of Materials Science and Engineering, Tianjin Polytechnic University, Chenglin Street 63, Tianjin City 300160, P. R. China
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  • Eduardo Cuervo Reyes,

    1. Laboratorium für Anorganische Chemie, Eidgenössische Technische Hochschule, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
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  • Michael Wörle,

    1. Laboratorium für Anorganische Chemie, Eidgenössische Technische Hochschule, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
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  • Prof. Dr. Reinhard Nesper

    Corresponding author
    1. Laboratorium für Anorganische Chemie, Eidgenössische Technische Hochschule, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
    2. Collegium Helveticum, Schmelzbergstrasse 25, 8092 Zürich, Switzerland
    • , Fax: +41-44-632-1149
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  • In Memory of Professor Hans-Georg von Schnering

Abstract

Three modifications of LiSr2Ge3 were prepared by solid state syntheses at high temperatures under inert conditions in sealed niobium ampoules. α-LiSr2Ge3 [space group Pnnm (No. 58), a = 11.102(1), b = 11.862(1), c = 4.631(1) Å, Z = 2] is isostructural to LiCa2Tt3 (Tt = Si, Ge), containing a one-dimensional infinite germanium chain in (tttctc)n conformation. β-LiSr2Ge3 [space group Fmmm (No. 69), a = 8.733(1), b = 8.996(1), c = 15.045(2) Å, Z = 4] crystallizes with the AgCa2Si3 structure. The β-phase shows a tendency for lithium deficiency, which may be as small as 6 % but can be larger. γ-LiSr2Ge3 [space group Fddd (No. 70), a = 8.675(3), b = 15.066(5), c = 18.258(5) Å, Z = 8] is isostructural to LiBa2Tt3. The latter two structures contain planar and distorted Ge6-rings, respectively. Comparison of the structures reveals significant changes of lattice parameters and bond lengths. β-LiSr2Ge3 may be stabilized by a slightly smaller lithium content due to preparation procedure. This assumption is supported by the structure analysis and total energy calculations. LiSr2Ge3 can be formulated as (Li+)2(Sr2+)4[Ge6]10– according to the Zintl–Klemm concept, with each of the Zintl anions having a partially occupied delocalized π* system. Theoretical investigations indicate metallic properties since π* bands are crossing the Fermi level. Phase widths were explored for Ge/Si and Sr/Eu exchange and complete miscibility was found for both series. Mixed silicide germanides exclusively crystallize in form of the γ-phase, whereas the Eu-containing mixed phases prefer the α-form, both throughout the series.

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