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Published February 19, 2018 | Supplemental Material
Journal Article Open

Zintl Ions within Framework Channels: The Complex Structure and Low-Temperature Transport Properties of Na_4Ge_(13)

Abstract

Single crystals of a complex Zintl compound with the composition Na_4Ge_(13) were synthesized for the first time using a high-pressure/high-temperature approach. Single-crystal diffraction of synchrotron radiation revealed a hexagonal crystal structure with P6/m space group symmetry that is composed of a three-dimensional sp^3 Ge framework punctuated by small and large channels along the crystallographic c axis. Na atoms are inside hexagonal prism-based Ge cages along the small channels, while the larger channels are occupied by layers of disordered sixfold Na rings, which are in turn filled by disordered [Ge_4]^(4–) tetrahedra. This compound is the same as "Na_(1–x)Ge_(3+z)" reported previously, but the availability of single crystals allowed for more complete structural determination with a formula unit best described as Na_4Ge_(12)(Ge_4)_(0.25). The compound is the first known example of a guest–host structure where discrete Zintl polyanions are confined inside the channels of a three-dimensional covalent framework. These features give rise to temperature-dependent disorder, as confirmed by first-principles calculations and physical properties measurements. The availability of single-crystal specimens allowed for measurement of the intrinsic low-temperature transport properties of this material and revealed its semiconductor behavior, which was corroborated by theoretical calculations.

Additional Information

© 2018 American Chemical Society. Received: November 16, 2017. Publication Date (Web): February 5, 2018. We are grateful to Dr. R. Hoffmann for valuable input and for providing us with computational resources. We thank Dr. D. Y. Kim for useful discussions, Dr. Y. Fei for guidance using the multianvil press, Dr. D. Popov for assistance with XRD measurements at the APS, and Dr. S. Teat for the opportunity to use beamline 11.3.1 at the ALS. This work was supported as part of the Energy Frontier Research in Extreme Environments (EFree) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, under Award DE-SC0001057. Facilities and instrumentation support were provided by the following: Transport properties measurements and data analyses performed at USF were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering, under Award DE-FG02-04ER46145. Single-crystal diffraction experiments performed on beamline 11.3.1 at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-AC02-05CH11231. Work at the ALS was also partially supported by the Consortium for Materials Properties Research in Earth Sciences (COMPRES) under NSF Cooperative Agreement EAR 1606856. Single-crystal diffraction experiments were also performed at HPCAT (Sector 16) at the Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award DE-NA0001974 with partial instrumentation funding by NSF. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. Computational aspects of this work were partially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada (RGPIN-2016-06276) and Carleton University (Startup Grant 186853). The authors declare no competing financial interest.

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August 19, 2023
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October 18, 2023