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Thermochemistry, Morphology, and Optical Characterization of Germanium Allotropes

Zaikina, Julia V. and Muthuswamy, Elayaraja and Lilova, Kristina I. and Gibbs, Zachary M. and Zeilinger, Michael and Snyder, G. Jeffrey and Fässler, Thomas F. and Navrotsky, Alexandra and Kauzlarich, Susan M. (2014) Thermochemistry, Morphology, and Optical Characterization of Germanium Allotropes. Chemistry of Materials, 26 (10). pp. 3263-3271. ISSN 0897-4756.

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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 Li_7Ge_(12) 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 Li_7Ge_(12). Investigation by diffuse reflectance infrared Fourier transform spectroscopy and UV–vis diffuse reflectance measurements reveal band gaps in agreement with quantum chemical calculations.

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Snyder, G. Jeffrey0000-0003-1414-8682
Additional Information:© 2014 American Chemical Society. Received: March 24, 2014. Published: April 21, 2014. We thank Alan Hicklin (Spectral Imaging Facility, NEAT ORU, University of California, Davis, CA) for AFM studies, Dr. Artem Abakumov (EMAT, University of Antwerp, Antwerp, Belgium) for fruitful discussion, Dr. Oliver Janka (University of California, Davis, CA) for EDXS analysis, and Joel Commisso (Interdisciplinary Center for Plasma Mass Spectrometry, University of California, Davis, CA) for ICP-MS. Financial support from the National Science Foundation (Grant DMR- 1035468) is gratefully acknowledged. Calorimetry was supported by the U.S. Department of Energy (Grant DE-FG02- 03ER46053). J.V.Z. thanks University of California (Davis, CA), and Z.M.G. and G.J.S. thank the National Aeronautics and Space Administration Jet Propulsion Laboratory for financial support. Z.M.G. and G.J.S. thank the Molecular Materials Research Center at Caltech for allowing use of instruments to obtain optical data for this work. S.M.K. and T.F. thank the Bavaria California Technology Center (BaCaTeC).
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Department of Energy (DOE)DE-FG02-03ER46053
University of California, DavisUNSPECIFIED
Issue or Number:10
Record Number:CaltechAUTHORS:20140627-105132703
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Official Citation: 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, and Susan M. Kauzlarich Chemistry of Materials 2014 26 (10), 3263-3271
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46552
Deposited By: Ruth Sustaita
Deposited On:27 Jun 2014 18:15
Last Modified:03 Oct 2019 06:45

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