Intercalation materials from azamacrocycles and layered sulfides: electrical and electrochemical behaviour

Abstract

The intercalation of poly-oxo-aza-macrocyclic compounds (azacrowns, AZC) in layered sulfides, such as TiS₂ and TaS₂, giving MS₂(AZC)_n (M = Ta, Ti; n ≈ 0.2) compounds, takes place at 200 °C during 2 days of contact time between the MS₂ and the AZC in the absence of air. The basal spacing increase of about 0.4 nm is compatible with the thickness of the macrocycle in a pseudo-planar arrangement between the sulfide layers. The intercalation compounds exhibit good thermal stability. The TaS₂ derivatives show superconducting behaviour with T_c values close to 3 K. The resistivity of pristine sulfides is strongly increased by the AZC intercalation. Electrochemical insertion of lithium could be carried out in a reversible manner, the diffusion coefficients, determined from GITT pulse-relaxation experiments, being two orders of magnitude lower than in Li intercalation of the pristine sulfides.