On the clathrate form of elemental silicon, Si136:: preparation and characterisation of NaxSi136 (X → 0)

The clathrate form of silicon, Si-136 (otherwise known as Si-34), having a residual sodium content as low as 35 ppm (i.e., x similar to 0.0058 in NaxSi136), has been prepared by thermal decomposition of NaSi under high vacuum, followed by several other treatments under vacuum, and completed by repeated reactions with iodine. The residual amount of sodium has been determined by a combination of analytic and spectroscopic methods involving XRD, electron probe microanalysis, atomic absorption, NMR and EPR. This latter technique proved to be very appropriate to the characterisation of very diluted sodium atoms in such clathrate structure and to the quantitative determination of its residual concentration. (C) 2004 Elsevier SAS. All rights reserved.