Sodium Intercalation into (PbS)1.18(TiS2)2Misfit Layer Compound

The misfit layer sulfide of composition (PbS)1.18(TiS2)2has been studied as a host material for the intercalation of sodium. The discharge curve profile using propylene carbonate (PC) as the solvent of electrolyte showed that the intercalation process is complex with the appearance of an extended plateau which suggests the formation of a multiphase region. In fact, an intermediate phase of sodium content 0.2 mol per formula unit, with basal spacing of 29.9 A, which exceeds by 12.4 A the repeating unit PbS–TiS2–TiS2, has been observed. This result is interpreted on the basis of solvent cointercalation. PC molecules are located at the interlayer region defined at the interface TiS2–TiS2. The increase in the sodium content promotes the release of PC molecules out of the layers. The interlayer expansion of the new phase formed is similar to that observed upon intercalation with sodium naftalide and is consistent with the location of sodium ions in the interstitial sites defined by two consecutive sulfur slabs. Under room conditions this phase absorbs water. The final expansion of ca. 6 A is consistent with a bilayer hydration process.