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Issue 40, 2014
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Structural and thermodynamic similarities of phases in the Li–Tt (Tt = Si, Ge) systems: redetermination of the lithium-rich side of the Li–Ge phase diagram and crystal structures of Li17Si4.0−xGex for x = 2.3, 3.1, 3.5, and 4 as well as Li4.1Ge

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Abstract

A reinvestigation of the lithium-rich section of the Li–Ge phase diagram reveals the existence of two new phases, Li17Ge4 and Li4.10Ge (Li16.38Ge4). Their structures are determined by X-ray diffraction experiments of large single crystals obtained from equilibrated melts with compositions Li95Ge5 and Li85Ge15. Excess melt is subsequently removed through isothermal centrifugation at 400 °C and 530 °C, respectively. Li17Ge4 crystallizes in the space group F[4 with combining macron]3m (a = 18.8521(3) Å, V = 6700.1(2) Å3, Z = 20, T = 298 K) and Li4.10Ge (Li16.38Ge4) in Cmcm (a = 4.5511(2) Å, b = 22.0862(7) Å, c = 13.2751(4) Å, V = 1334.37(8) Å3, Z = 16, T = 123 K). Both phases are isotypic with their Si counterparts and are further representative of the Li17Pb4 and Li4.11Si structure types. Additionally, the solid solutions Li17Si4−xGex follows Vegard's law. A comparison of the GeLin coordination polyhedra shows that isolated Ge atoms are 13- and 14-coordinated in Li17Ge4, whereas in Li16.38Ge4 the Ge atoms possess coordination numbers 12 and 13. Regarding the thermodynamic stability, Li16.38Ge4 is assigned a high-temperature phase existing between ∼400 °C and 627 °C, whereas Li17Ge4 decomposes peritectically at 520–522 °C. Additionally, the decomposition of Li16.38Ge4 below ∼400 °C was found to be very sluggish. These findings are manifested by differential scanning calorimetry, long-term annealing experiments and the results from melt equilibration experiments. Interestingly, the thermodynamic properties of the lithium-rich tetrelides Li17Tt4 and Li4.1Tt (Li16.4Tt4) are very similar (Tt = Si, Ge). Besides Li15Tt4, Li14Tt6, Li12Tt7, and LiTt, the title compounds are further examples of isotypic tetrelides in the systems Li–Tt.

Graphical abstract: Structural and thermodynamic similarities of phases in the Li–Tt (Tt = Si, Ge) systems: redetermination of the lithium-rich side of the Li–Ge phase diagram and crystal structures of Li17Si4.0−xGex for x = 2.3, 3.1, 3.5, and 4 as well as Li4.1Ge

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Publication details

The article was received on 12 Mar 2014, accepted on 12 May 2014 and first published on 13 May 2014


Article type: Paper
DOI: 10.1039/C4DT00743C
Citation: Dalton Trans., 2014,43, 14959-14970
  • Open access: Creative Commons BY-NC license
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    Structural and thermodynamic similarities of phases in the Li–Tt (Tt = Si, Ge) systems: redetermination of the lithium-rich side of the Li–Ge phase diagram and crystal structures of Li17Si4.0−xGex for x = 2.3, 3.1, 3.5, and 4 as well as Li4.1Ge

    M. Zeilinger and T. F. Fässler, Dalton Trans., 2014, 43, 14959
    DOI: 10.1039/C4DT00743C

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