EXAFS STUDIES OF SODIUM INTERCALATED 2H AND 1T POLYTYPES OF TAS2

Na intercalated 2H and 1T polytypes of TaS2 have been studied by exten ded X-ray absorption fine-structure (EXAFS) experiments. The intercala ted compounds were prepared by in situ evaporation of Na to the (0001) cleaved surface of the TaS2 crystal. The EXAFS analysis shows that in tercalated sodium atoms are positioned in the van der Waals gap in a s ixfold coordinated site, giving rise to an increase of the gap width b y 1.3 +/- 0.06 Angstrom far the 2H polytype and 1.5 +/- 0.06 Angstrom for the 1T polytype. The corresponding Na-S nearest neighbour distance s are 2.85 +/- 0.05 and 2.95 +/- 0.05 Angstrom, respectively. With an increasing amount of deposited Na, a fraction of sodium atoms remains on the surface. The adsorbed Na atoms occupy a threefold hollow site o n the surface with a Na-S bond length of 2.80 +/- 0.05 Angstrom for th e 2H polytype and 2.91 +/- 0.05 Angstrom for the 1T polytype.