Time-resolved in situ synchrotron X-ray diffraction studies of type 1 silicon clathrate formation

  1. Get@NRC: Time-resolved in situ synchrotron X-ray diffraction studies of type 1 silicon clathrate formation (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1021/cm2018136
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Journal titleChemistry of Materials
Pages51605167; # of pages: 8
SubjectAmorphous phase; Clathrate formation; Clathrate phase; Controlled temperature; Cubic unit cells; Formation mechanism; High temperature; In-situ; In-Situ Study; In-situ synchrotrons; Metal atoms; Na atoms; NaSi; Open frameworks; Polyanions; Sealed tubes; Silicon clathrates; Solid-state synthesis; Structure and properties; Time-resolved; Vacuum condition; X ray reflection; X-ray detections; Zintl phase; Barium; Inert gases; Nuclear magnetic resonance spectroscopy; Pyrolysis; Silicon; Sodium; Synchrotron radiation; Synchrotrons; Synthesis (chemical); Thermodynamic properties; Vacuum; X ray diffraction; Crystal atomic structure
AbstractSilicon clathrates are unusual open-framework solids formed by tetrahedrally bonded silicon that show remarkable electronic and thermal properties. The type I structure has a primitive cubic unit cell containing cages occupied by metal atoms to give compositions such as Na8Si 46 and Na2Ba6Si46. Although their structure and properties are well described, there is little understanding of the formation mechanism. Na8Si46 is typically produced by metastable thermal decomposition under vacuum conditions from NaSi, itself an unusual structure containing Si4 4- polyanions. In this study, we used in situ synchrotron X-ray diffraction combined with rapid X-ray detection on samples taken through a controlled temperature ramp (25-500 °C at 8 °C/min) under vacuum conditions (10-4 bar) to study the clathrate formation reaction. We also carried out complementary in situ high-temperature solid-state 23Na NMR experiments using a sealed tube loaded under inert-gas-atmosphere conditions. We find no evidence for an intermediate amorphous phase during clathrate formation. Instead, we observe an unexpectedly high degree of structural coherency between the Na 8Si46 clathrate and its NaSi precursor, evidenced by a smooth passage of several X-ray reflections from one structure into the other. The results indicate the possibility of an unusual, epitaxial-like, growth of the clathrate phase as Na atoms are removed from the NaSi precursor into the vacuum. © 2011 American Chemical Society.
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AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21271697
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Record identifiera9c9aae3-0823-4d39-bd60-fd44b4c80a7e
Record created2014-03-24
Record modified2016-05-09
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