High-Tc fullerides

Highlights: • In addition to the critical temperature calculation, our article explains the relation of the electronic and structural parameters to phonon property, such as phonon frequencies and electron-phonon coupling. • We explore an alternative to adapt BCS using structural and electronic properties of the crystal and its components to calculated the critical temperature of the alkali-metal fulleride superconductors. • The combination of parameters in Table 1 can explain the dependence of the critical temperature to Hubbard U. -- Abstract: The critical temperature of the fulleride superconductors A₂BC₆₀ (A, B = Na, K, Rb, Cs) with the alkali metals solvated with ammonia, methylamine, and water molecules is calculated using a multivariate analysis of the lattice parameter, ionic radius, electronegativity, and other electronic properties obtained from density functional theory calculations. Results are in good agreement with the experimental data both for the alkali-metal fullerides and for the solvated (NH₃)₄Na₂CsC₆₀, (CH₃NH₂)K₃C₆₀ and (NH₃)K₃C₆₀ compounds. The expansion of the crystalline lattice and the increase of the ionic character of the chemical bonds with solvation of the metal can modify significantly the critical temperature of the material. In the ammoniation of Na₂CsC_60, there occurs an expansion of the lattice and an increase of the ionic character of the chemical bonds in the material, which increases its critical temperature by about 20 K. Methylamine also can raise the critical temperature but is not as efficient as ammonia. Our results suggest that hydration of Na₃C₆₀ leads to the superconducting state and that (H₂O)₄Cs₃C₆₀ is a high-T_c fulleride at 50.9 K.