Preparation and superconductivity of intercalation compounds of TiNCl with aliphatic amines

Abstract

Intercalation compounds of TiNCl with n-alkyl monoamines (C_nH_2n+1NH₂, 3 ≤ n ≤ 12) and alkylene diamines (H₂NC_nH_2nNH₂, 2 ≤ n ≤ 12) have been prepared. Upon intercalation of monoamines, the basal spacing of TiNCl expanded from 7.8 Å to a value in the range of 12.0 to 37 Å, with the alkyl chains oriented in various ways; the stacking of TiNCl layers became turbostratic disordered. Diamines show only a limited expansion of the basal spacing in a range of 11.1 to 12.3 Å with the alkylene chains oriented parallel to TiNCl layers which are mutually shifted along the a- and b-axes in the ab plane, and stacked to form new polytypes with the space group Bmmb or Immm different from Pmmn of the pristine TiNCl. Only diamine intercalated compounds showed superconductivity with the transition temperatures (T_c's) ranging from 6.8 to 17.1 K. The intercalation compounds with diamine molecules with longer alkylene chains tend to exhibit higher T_c's; the compounds with diamines with an even number of carbon atoms tend to have larger superconducting volume fractions. Superconductivities of the intercalation compounds with N,N′-substituted alkylene diamines have been examined, which also showed superconductivity with T_c's in the range of 8.6–15.8 K. It is likely that the charge transfer of the lone pair electrons of amino groups may change the semiconductor TiNCl to superconductors with ordered stacking structures.