Thermochemistry, morphology, and optical characterization of germanium allotropes

Julia V. Zaikina, Elayaraja Muthuswamy, Kristina I. Lilova, Zachary M. Gibbs, Michael Zeilinger, G. Jeffrey Snyder, Thomas F. Fässler, Alexandra Navrotsky, Susan M. Kauzlarich

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14 Scopus citations

Abstract

A thermochemical study of three germanium allotropes by differential scanning calorimetry (DSC) and oxidative high-temperature drop solution calorimetry with sodium molybdate as the solvent is described. Two allotropes, microcrystalline allo-Ge (m-allo-Ge) and 4H-Ge, have been prepared by topotactic deintercalation of Li7Ge12 with methanol (m-allo-Ge) and subsequent annealing at 250 °C (4H-Ge). Transition enthalpies determined by differential scanning calorimetry amount to 4.96(5) ± 0.59 kJ/mol (m-allo-Ge) and 1.46 ± 0.55 kJ/mol (4H-Ge). From high-temperature drop solution calorimetry, they are energetically less stable by 2.71 ± 2.79 kJ/mol (m-allo-Ge) and 5.76 ± 5.12 kJ/mol (4H-Ge) than α-Ge, which is the stable form of germanium under ambient conditions. These data are in agreement with DSC, as well as with the previous quantum chemical calculations. The morphology of the m-allo-Ge and 4H-Ge crystallites was investigated by a combination of scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Even though the crystal structures of m-allo-Ge and 4H-Ge cannot be considered as truly layered, these phases retain the crystalline morphology of the layered precursor Li7Ge12. Investigation by diffuse reflectance infrared Fourier transform spectroscopy and UV-vis diffuse reflectance measurements reveal band gaps in agreement with quantum chemical calculations.

Original languageEnglish (US)
Pages (from-to)3263-3271
Number of pages9
JournalChemistry of Materials
Volume26
Issue number10
DOIs
StatePublished - May 27 2014

ASJC Scopus subject areas

  • Materials Chemistry
  • Chemical Engineering(all)
  • Chemistry(all)

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    Zaikina, J. V., Muthuswamy, E., Lilova, K. I., Gibbs, Z. M., Zeilinger, M., Snyder, G. J., Fässler, T. F., Navrotsky, A., & Kauzlarich, S. M. (2014). Thermochemistry, morphology, and optical characterization of germanium allotropes. Chemistry of Materials, 26(10), 3263-3271. https://doi.org/10.1021/cm5010467