Fullerene lattice hydrogen

Figure 14. Unit cells of fullerite with bcc (a) and fee (b) structures with lattice hydrogen only. (Shaded circle) Sites of crystalline lattices, in which fullerenes molecules are distributed ( ) octahedral (O) interstitial sites (o) tetrahedral...

Hence the statistical and thermodynamical theory of the lattice hydrogen solubility in fee fullerite with consideration for the hydrogen atoms distribution over the interstitial sites of different types has allowed us to explain and justify the formation of HX hydrofullerites with high hydrogen concentration when 0 < x < 18. It has been found that hydrogen solubility depends on the fullerite composition, its temperature, the order parameter in i = C6o, 2 = C70 fullerenes distribution over the lattice sites, the energetic constants characterizing the interaction between H- pairs at the different distances. 

For solving the problem the free energies fj (i = 1, 2, 3) of respective d>Pt, calculated using the average energies method, then-dependences on temperature, the c, c2, x concentrations of C6o, C70 fullerenes and hydrogen, the order parameter r in distribution of fullerenes over the lattice sites and energetic constants have been defined. 

Considering formulae (8), (10), (12), the calculation of free energy f3 for one lattice site for the 4>HX hydrofullerite in dependence on temperature T, concentrations Ci, c2, c of 4>i, d>2 fullerenes and hydrogen atoms, order parameter r 3 in this phase and energetic constants gives the following formula ... 

Formulae (60) and (63) with regard to the relations (61) and (47) determine the corresponding hydrogen solubilities in dependence on the fullerite composition (ci, c2 concentrations), temperature, degree of the long-range order in the fullerenes distribution over the lattice sites, and the energetic constants. 

The expression for free energy f3 of this phase involves the terms of free energy f3 of the 4>Pt phase, depending on the energies of pair interaction between fullerenes n- 4>m and their distribution over the lattice sites of the first and the second type, and the terms of free energy f2 with energetic parameters of hydrogen atoms in positions and Q. 

The hydrogen solubility in each phase is defined by the equilibrium concentration of hydrogen atoms that can be found by minimization of free energies f2, f3 with respect to concentration x of hydrogen atoms relative to the number of sites (fullerenes) of crystal lattice ... 

The process of hydride formation in the fuUerites consists of two steps saturation of the fullerite lattice with mobile hydrogen and the hydrogenation of fullerene molecules by excess mobile hydrogen. There are various methods for... 

Carbon atoms with sp hybridization offer a fascinating example for the transition from the infinite crystal lattice to the molecular state. In this case, not 6, 10, or 14, but 60 carbon atoms are used as cutouts of the lattice, and the free valencies are not saturated by hydrogen atoms such nano sized cutouts are too small to exist as a stable graphitic structure and consequently they create a spheric shape consisting of five- and six membered rings with altogether 60 vertices, the famous soccer-like so-called fullerene, CgQ. 

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