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Title: The Local Atomic Structure and Chemical Bonding in Sodium Tin Phases

To understand these electrochemically-derived materials we have reinvestigated the formation of Na-Sn alloys to identify all the phases which form when x ≥ 1 (NaxSn) and characterized the local bonding around the Sn atoms with X-ray diffraction, 119Sn M ssbauer spectroscopy, and X-ray absorption spectroscopies. The results from the well-defined crystallographic materials were compared to the spectroscopic measurements of the local Sn structures in the electrochemically prepared materials. The reinvestigation of the Na-Sn compounds yields a number of new results: (i) Na7Sn3 is a new thermodynamically-stable phase with a rhombohedral structure and R-3m space group; (ii) orthorhombic Na9Sn4 (Cmcm) has relatively slow formation kinetics suggesting why it does not form at room temperature during the electrochemical reaction; (iii) orthorhombic Na14.78Sn4 (Pnma), better described as Na16-xSn4, is Na-richer than cubic Na15Sn4 (I-43d). Characterization of electrochemically prepared Na-Sn alloys indicate that, at the exception of Na7Sn3 and Na15Sn4, different crystal structures than similar Na-Sn compositions prepared via classic solid state reactions are formed. These phases are composed of disordered structures characteristic of kinetic-driven solid-state amorphization reactions. In these structures, Sn coordinates in asymmetric environments, which differ significantly from the environments present in Na-Sn model compounds.
 [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [1] ;  [3] ;  [4] ;  [4] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. Montpellier II (France)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Materials Chemistry. A
Additional Journal Information:
Journal Volume: 2; Journal Issue: 44; Journal ID: ISSN 2050-7488
Royal Society of Chemistry
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Sodium ion reaction of tin (Sn) anodes; Sodium tin phase diagram; 119Sn Mössbauer spectroscopy; X-ray and neutron diffractions; R-3m Na7Sn3 new phase; Sn K-edge EXAFS; Na K-edge and Sn M5,4-edge XANES