Preparation and superconducting behavior of triammonium fulleride

The synthesis of triammonium fulleride (NH4)(3)C-60 by ion exchange of either K3C60 or Rb3C60 with NH4Cl in absolute toluene is reported. According to the Rietveld refinement of a synchrotron radiation-based Xray diffraction pattern, (NH4)(3)C-60 belongs to the same structure type as both K3C60 and Rb3C60 featuring an fcc lattice with intercalated cations occupying tetrahedral and octahedral cavities of the close-packing formed by fullerene C-60 spheres. The ion exchange is incomplete and the final formulation of the product is [(NH4)(2.88)K-0.12]C-60. In contrast to earlier suggestions and tabulated ionic radii values, the (NH4)(3)C-60 crystal structure is characterized by a lattice parameter slightly smaller than that of K3C60. A similar reaction between K4C60 and NH4Cl proceeds differently involving the redox step and affords [(NH4)(0.48)K-2.52]C-60 again emphasizing the fact that ammonium and potassium in the fulleride phase tend to form substitutional solid solutions. According to low-frequency inductive method, all (NH4)(3)C-60-related phases studied are superconducting with similar temperatures of the superconducting transition around T-c = 16.4 K. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The synthesis of triammonium fulleride by ion exchange, the crystal structure similarities between (NH4)(3)C-60 and K3C60, as well as the tendency of ammonium and potassium to form solid solutions in the fulleride phase were investigated. The superconductivity of (NH4)(3)C-60-related phases was also confirmed with similar transition temperatures around 16.4 K.