Electrochemical lithium and sodium intercalation into TaFe_1.25Te₃

Abstract

Lithium and sodium have been topotactically inserted in the lattice of TaFe_1.25Te₃ by electrochemical procedures. The existence of electronically unequivalent sites occupied by tellurium atoms conditions a two-step insertion process. In each step, the alkali metal ions occupy empty sites in the structure which are coordinated by tellurium atoms of a different set of sites. The␣thermodynamic and kinetic parameters of Li _x TaFe_1.25Te₃ and Na _x TaFe_1.25Te₃ have been determined and compared with other inserted binary and ternary chalcogenides. The values of the free energy of intercalation are less negative than those previously reported for TaTe₂ and close to those found for the misfit layer compound (PbS)_1.13TaS₂. The values of alkali metal ion diffusivity are closer to those reported for the binary telluride, due to the similarities in the atoms exposed to the interlayer space.