Abstract
To understand the electrochemically-derived Na-Sn 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 Mössbauer 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 R3m 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 (I43d). Characterization of electrochemically prepared Na-Sn alloys indicate that, with 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.
Original language | English |
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Pages (from-to) | 18959-18973 |
Number of pages | 15 |
Journal | Journal of Materials Chemistry A |
Volume | 2 |
Issue number | 44 |
DOIs | |
State | Published - Nov 28 2014 |